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JVM源码分析之G1垃圾收集器分析一
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<p>对 Java 的 gc 实现比较感兴趣，原先一般都是看周志明的书，但其实并没有讲具体的 gc 源码，而是把整个思路和流程讲解了一下<br>特别是 G1 的具体实现<br>一般对 G1 的理解其实就是把原先整块的新生代老年代分成了以 region 为单位的小块内存，简而言之，就是原先对新生代老年代的收集会涉及到整个代的堆内存空间，而G1 把它变成了更细致的小块内存<br>这带来了一个很明显的好处和一个很明显的坏处，好处是内存收集可以更灵活，耗时会变短，但整个收集的处理复杂度就变高了<br>目前看了一点点关于 G1 收集的预期时间相关的代码</p>
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<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br></pre></td><td class="code"><pre><span class="line"><span class="function">HeapWord* <span class="title">G1CollectedHeap::do_collection_pause</span><span class="params">(<span class="keyword">size_t</span> word_size,</span></span></span><br><span class="line"><span class="function"><span class="params"> uint gc_count_before,</span></span></span><br><span class="line"><span class="function"><span class="params"> <span class="keyword">bool</span>* succeeded,</span></span></span><br><span class="line"><span class="function"><span class="params"> GCCause::Cause gc_cause)</span> </span>{</span><br><span class="line"> assert_heap_not_locked_and_not_at_safepoint();</span><br><span class="line"> <span class="function">VM_G1CollectForAllocation <span class="title">op</span><span class="params">(word_size,</span></span></span><br><span class="line"><span class="function"><span class="params"> gc_count_before,</span></span></span><br><span class="line"><span class="function"><span class="params"> gc_cause,</span></span></span><br><span class="line"><span class="function"><span class="params"> <span class="literal">false</span>, <span class="comment">/* should_initiate_conc_mark */</span></span></span></span><br><span class="line"><span class="function"><span class="params"> g1_policy()->max_pause_time_ms())</span></span>;</span><br><span class="line"> VMThread::execute(&op);</span><br><span class="line"></span><br><span class="line"> HeapWord* result = op.result();</span><br><span class="line"> <span class="keyword">bool</span> ret_succeeded = op.prologue_succeeded() && op.pause_succeeded();</span><br><span class="line"> assert(result == <span class="literal">NULL</span> || ret_succeeded,</span><br><span class="line"> <span class="string">"the result should be NULL if the VM did not succeed"</span>);</span><br><span class="line"> *succeeded = ret_succeeded;</span><br><span class="line"></span><br><span class="line"> assert_heap_not_locked();</span><br><span class="line"> <span class="keyword">return</span> result;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>这里就是收集时需要停顿的，其中<code>VMThread::execute(&op);</code>是具体执行的，真正执行的是<code>VM_G1CollectForAllocation::doit</code>方法</p>
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<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">VM_G1CollectForAllocation::doit</span><span class="params">()</span> </span>{</span><br><span class="line"> G1CollectedHeap* g1h = G1CollectedHeap::heap();</span><br><span class="line"> assert(!_should_initiate_conc_mark || g1h->should_do_concurrent_full_gc(_gc_cause),</span><br><span class="line"> <span class="string">"only a GC locker, a System.gc(), stats update, whitebox, or a hum allocation induced GC should start a cycle"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (_word_size > <span class="number">0</span>) {</span><br><span class="line"> <span class="comment">// An allocation has been requested. So, try to do that first.</span></span><br><span class="line"> _result = g1h->attempt_allocation_at_safepoint(_word_size,</span><br><span class="line"> <span class="literal">false</span> <span class="comment">/* expect_null_cur_alloc_region */</span>);</span><br><span class="line"> <span class="keyword">if</span> (_result != <span class="literal">NULL</span>) {</span><br><span class="line"> <span class="comment">// If we can successfully allocate before we actually do the</span></span><br><span class="line"> <span class="comment">// pause then we will consider this pause successful.</span></span><br><span class="line"> _pause_succeeded = <span class="literal">true</span>;</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="function">GCCauseSetter <span class="title">x</span><span class="params">(g1h, _gc_cause)</span></span>;</span><br><span class="line"> <span class="keyword">if</span> (_should_initiate_conc_mark) {</span><br><span class="line"> <span class="comment">// It's safer to read old_marking_cycles_completed() here, given</span></span><br><span class="line"> <span class="comment">// that noone else will be updating it concurrently. Since we'll</span></span><br><span class="line"> <span class="comment">// only need it if we're initiating a marking cycle, no point in</span></span><br><span class="line"> <span class="comment">// setting it earlier.</span></span><br><span class="line"> _old_marking_cycles_completed_before = g1h->old_marking_cycles_completed();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// At this point we are supposed to start a concurrent cycle. We</span></span><br><span class="line"> <span class="comment">// will do so if one is not already in progress.</span></span><br><span class="line"> <span class="keyword">bool</span> res = g1h->g1_policy()->force_initial_mark_if_outside_cycle(_gc_cause);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// The above routine returns true if we were able to force the</span></span><br><span class="line"> <span class="comment">// next GC pause to be an initial mark; it returns false if a</span></span><br><span class="line"> <span class="comment">// marking cycle is already in progress.</span></span><br><span class="line"> <span class="comment">//</span></span><br><span class="line"> <span class="comment">// If a marking cycle is already in progress just return and skip the</span></span><br><span class="line"> <span class="comment">// pause below - if the reason for requesting this initial mark pause</span></span><br><span class="line"> <span class="comment">// was due to a System.gc() then the requesting thread should block in</span></span><br><span class="line"> <span class="comment">// doit_epilogue() until the marking cycle is complete.</span></span><br><span class="line"> <span class="comment">//</span></span><br><span class="line"> <span class="comment">// If this initial mark pause was requested as part of a humongous</span></span><br><span class="line"> <span class="comment">// allocation then we know that the marking cycle must just have</span></span><br><span class="line"> <span class="comment">// been started by another thread (possibly also allocating a humongous</span></span><br><span class="line"> <span class="comment">// object) as there was no active marking cycle when the requesting</span></span><br><span class="line"> <span class="comment">// thread checked before calling collect() in</span></span><br><span class="line"> <span class="comment">// attempt_allocation_humongous(). Retrying the GC, in this case,</span></span><br><span class="line"> <span class="comment">// will cause the requesting thread to spin inside collect() until the</span></span><br><span class="line"> <span class="comment">// just started marking cycle is complete - which may be a while. So</span></span><br><span class="line"> <span class="comment">// we do NOT retry the GC.</span></span><br><span class="line"> <span class="keyword">if</span> (!res) {</span><br><span class="line"> assert(_word_size == <span class="number">0</span>, <span class="string">"Concurrent Full GC/Humongous Object IM shouldn't be allocating"</span>);</span><br><span class="line"> <span class="keyword">if</span> (_gc_cause != GCCause::_g1_humongous_allocation) {</span><br><span class="line"> _should_retry_gc = <span class="literal">true</span>;</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">return</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Try a partial collection of some kind.</span></span><br><span class="line"> _pause_succeeded = g1h->do_collection_pause_at_safepoint(_target_pause_time_ms);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (_pause_succeeded) {</span><br><span class="line"> <span class="keyword">if</span> (_word_size > <span class="number">0</span>) {</span><br><span class="line"> <span class="comment">// An allocation had been requested. Do it, eventually trying a stronger</span></span><br><span class="line"> <span class="comment">// kind of GC.</span></span><br><span class="line"> _result = g1h->satisfy_failed_allocation(_word_size, &_pause_succeeded);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">bool</span> should_upgrade_to_full = !g1h->should_do_concurrent_full_gc(_gc_cause) &&</span><br><span class="line"> !g1h->has_regions_left_for_allocation();</span><br><span class="line"> <span class="keyword">if</span> (should_upgrade_to_full) {</span><br><span class="line"> <span class="comment">// There has been a request to perform a GC to free some space. We have no</span></span><br><span class="line"> <span class="comment">// information on how much memory has been asked for. In case there are</span></span><br><span class="line"> <span class="comment">// absolutely no regions left to allocate into, do a maximally compacting full GC.</span></span><br><span class="line"> log_info(gc, ergo)(<span class="string">"Attempting maximally compacting collection"</span>);</span><br><span class="line"> _pause_succeeded = g1h->do_full_collection(<span class="literal">false</span>, <span class="comment">/* explicit gc */</span></span><br><span class="line"> <span class="literal">true</span> <span class="comment">/* clear_all_soft_refs */</span>);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> guarantee(_pause_succeeded, <span class="string">"Elevated collections during the safepoint must always succeed."</span>);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> assert(_result == <span class="literal">NULL</span>, <span class="string">"invariant"</span>);</span><br><span class="line"> <span class="comment">// The only reason for the pause to not be successful is that, the GC locker is</span></span><br><span class="line"> <span class="comment">// active (or has become active since the prologue was executed). In this case</span></span><br><span class="line"> <span class="comment">// we should retry the pause after waiting for the GC locker to become inactive.</span></span><br><span class="line"> _should_retry_gc = <span class="literal">true</span>;</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>这里可以看到核心的是<code>G1CollectedHeap::do_collection_pause_at_safepoint</code>这个方法，它带上了目标暂停时间的值</p>
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class="line">302</span><br><span class="line">303</span><br><span class="line">304</span><br><span class="line">305</span><br><span class="line">306</span><br><span class="line">307</span><br><span class="line">308</span><br><span class="line">309</span><br><span class="line">310</span><br><span class="line">311</span><br><span class="line">312</span><br><span class="line">313</span><br><span class="line">314</span><br><span class="line">315</span><br><span class="line">316</span><br><span class="line">317</span><br><span class="line">318</span><br><span class="line">319</span><br><span class="line">320</span><br><span class="line">321</span><br><span class="line">322</span><br><span class="line">323</span><br><span class="line">324</span><br><span class="line">325</span><br><span class="line">326</span><br><span class="line">327</span><br><span class="line">328</span><br><span class="line">329</span><br><span class="line">330</span><br></pre></td><td class="code"><pre><span class="line">G1CollectedHeap::do_collection_pause_at_safepoint(<span class="keyword">double</span> target_pause_time_ms) {</span><br><span class="line"> assert_at_safepoint_on_vm_thread();</span><br><span class="line"> guarantee(!is_gc_active(), <span class="string">"collection is not reentrant"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (GCLocker::check_active_before_gc()) {</span><br><span class="line"> <span class="keyword">return</span> <span class="literal">false</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> _gc_timer_stw->register_gc_start();</span><br><span class="line"></span><br><span class="line"> GCIdMark gc_id_mark;</span><br><span class="line"> _gc_tracer_stw->report_gc_start(gc_cause(), _gc_timer_stw->gc_start());</span><br><span class="line"></span><br><span class="line"> <span class="function">SvcGCMarker <span class="title">sgcm</span><span class="params">(SvcGCMarker::MINOR)</span></span>;</span><br><span class="line"> ResourceMark rm;</span><br><span class="line"></span><br><span class="line"> g1_policy()->note_gc_start();</span><br><span class="line"></span><br><span class="line"> wait_for_root_region_scanning();</span><br><span class="line"></span><br><span class="line"> print_heap_before_gc();</span><br><span class="line"> print_heap_regions();</span><br><span class="line"> trace_heap_before_gc(_gc_tracer_stw);</span><br><span class="line"></span><br><span class="line"> _verifier->verify_region_sets_optional();</span><br><span class="line"> _verifier->verify_dirty_young_regions();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We should not be doing initial mark unless the conc mark thread is running</span></span><br><span class="line"> <span class="keyword">if</span> (!_cm_thread->should_terminate()) {</span><br><span class="line"> <span class="comment">// This call will decide whether this pause is an initial-mark</span></span><br><span class="line"> <span class="comment">// pause. If it is, in_initial_mark_gc() will return true</span></span><br><span class="line"> <span class="comment">// for the duration of this pause.</span></span><br><span class="line"> g1_policy()->decide_on_conc_mark_initiation();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We do not allow initial-mark to be piggy-backed on a mixed GC.</span></span><br><span class="line"> assert(!collector_state()->in_initial_mark_gc() ||</span><br><span class="line"> collector_state()->in_young_only_phase(), <span class="string">"sanity"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We also do not allow mixed GCs during marking.</span></span><br><span class="line"> assert(!collector_state()->mark_or_rebuild_in_progress() || collector_state()->in_young_only_phase(), <span class="string">"sanity"</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Record whether this pause is an initial mark. When the current</span></span><br><span class="line"> <span class="comment">// thread has completed its logging output and it's safe to signal</span></span><br><span class="line"> <span class="comment">// the CM thread, the flag's value in the policy has been reset.</span></span><br><span class="line"> <span class="keyword">bool</span> should_start_conc_mark = collector_state()->in_initial_mark_gc();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Inner scope for scope based logging, timers, and stats collection</span></span><br><span class="line"> {</span><br><span class="line"> EvacuationInfo evacuation_info;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (collector_state()->in_initial_mark_gc()) {</span><br><span class="line"> <span class="comment">// We are about to start a marking cycle, so we increment the</span></span><br><span class="line"> <span class="comment">// full collection counter.</span></span><br><span class="line"> increment_old_marking_cycles_started();</span><br><span class="line"> _cm->gc_tracer_cm()->set_gc_cause(gc_cause());</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> _gc_tracer_stw->report_yc_type(collector_state()->yc_type());</span><br><span class="line"></span><br><span class="line"> GCTraceCPUTime tcpu;</span><br><span class="line"></span><br><span class="line"> G1HeapVerifier::G1VerifyType verify_type;</span><br><span class="line"> <span class="function">FormatBuffer<> <span class="title">gc_string</span><span class="params">(<span class="string">"Pause Young "</span>)</span></span>;</span><br><span class="line"> <span class="keyword">if</span> (collector_state()->in_initial_mark_gc()) {</span><br><span class="line"> gc_string.append(<span class="string">"(Concurrent Start)"</span>);</span><br><span class="line"> verify_type = G1HeapVerifier::G1VerifyConcurrentStart;</span><br><span class="line"> } <span class="keyword">else</span> <span class="keyword">if</span> (collector_state()->in_young_only_phase()) {</span><br><span class="line"> <span class="keyword">if</span> (collector_state()->in_young_gc_before_mixed()) {</span><br><span class="line"> gc_string.append(<span class="string">"(Prepare Mixed)"</span>);</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> gc_string.append(<span class="string">"(Normal)"</span>);</span><br><span class="line"> }</span><br><span class="line"> verify_type = G1HeapVerifier::G1VerifyYoungNormal;</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> gc_string.append(<span class="string">"(Mixed)"</span>);</span><br><span class="line"> verify_type = G1HeapVerifier::G1VerifyMixed;</span><br><span class="line"> }</span><br><span class="line"> GCTraceTime(Info, gc) tm(gc_string, <span class="literal">NULL</span>, gc_cause(), <span class="literal">true</span>);</span><br><span class="line"></span><br><span class="line"> uint active_workers = AdaptiveSizePolicy::calc_active_workers(workers()->total_workers(),</span><br><span class="line"> workers()->active_workers(),</span><br><span class="line"> Threads::number_of_non_daemon_threads());</span><br><span class="line"> active_workers = workers()->update_active_workers(active_workers);</span><br><span class="line"> log_info(gc,task)(<span class="string">"Using %u workers of %u for evacuation"</span>, active_workers, workers()->total_workers());</span><br><span class="line"></span><br><span class="line"> <span class="function">TraceCollectorStats <span class="title">tcs</span><span class="params">(g1mm()->incremental_collection_counters())</span></span>;</span><br><span class="line"> <span class="function">TraceMemoryManagerStats <span class="title">tms</span><span class="params">(&_memory_manager, gc_cause(),</span></span></span><br><span class="line"><span class="function"><span class="params"> collector_state()->yc_type() == Mixed <span class="comment">/* allMemoryPoolsAffected */</span>)</span></span>;</span><br><span class="line"></span><br><span class="line"> <span class="function">G1HeapTransition <span class="title">heap_transition</span><span class="params">(<span class="keyword">this</span>)</span></span>;</span><br><span class="line"> <span class="keyword">size_t</span> heap_used_bytes_before_gc = used();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Don't dynamically change the number of GC threads this early. A value of</span></span><br><span class="line"> <span class="comment">// 0 is used to indicate serial work. When parallel work is done,</span></span><br><span class="line"> <span class="comment">// it will be set.</span></span><br><span class="line"></span><br><span class="line"> { <span class="comment">// Call to jvmpi::post_class_unload_events must occur outside of active GC</span></span><br><span class="line"> IsGCActiveMark x;</span><br><span class="line"></span><br><span class="line"> gc_prologue(<span class="literal">false</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (VerifyRememberedSets) {</span><br><span class="line"> log_info(gc, verify)(<span class="string">"[Verifying RemSets before GC]"</span>);</span><br><span class="line"> VerifyRegionRemSetClosure v_cl;</span><br><span class="line"> heap_region_iterate(&v_cl);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> _verifier->verify_before_gc(verify_type);</span><br><span class="line"></span><br><span class="line"> _verifier->check_bitmaps(<span class="string">"GC Start"</span>);</span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="meta-keyword">if</span> COMPILER2_OR_JVMCI</span></span><br><span class="line"> DerivedPointerTable::<span class="built_in">clear</span>();</span><br><span class="line"><span class="meta">#<span class="meta-keyword">endif</span></span></span><br><span class="line"></span><br><span class="line"> <span class="comment">// Please see comment in g1CollectedHeap.hpp and</span></span><br><span class="line"> <span class="comment">// G1CollectedHeap::ref_processing_init() to see how</span></span><br><span class="line"> <span class="comment">// reference processing currently works in G1.</span></span><br><span class="line"></span><br><span class="line"> <span class="comment">// Enable discovery in the STW reference processor</span></span><br><span class="line"> _ref_processor_stw->enable_discovery();</span><br><span class="line"></span><br><span class="line"> {</span><br><span class="line"> <span class="comment">// We want to temporarily turn off discovery by the</span></span><br><span class="line"> <span class="comment">// CM ref processor, if necessary, and turn it back on</span></span><br><span class="line"> <span class="comment">// on again later if we do. Using a scoped</span></span><br><span class="line"> <span class="comment">// NoRefDiscovery object will do this.</span></span><br><span class="line"> <span class="function">NoRefDiscovery <span class="title">no_cm_discovery</span><span class="params">(_ref_processor_cm)</span></span>;</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Forget the current alloc region (we might even choose it to be part</span></span><br><span class="line"> <span class="comment">// of the collection set!).</span></span><br><span class="line"> _allocator->release_mutator_alloc_region();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// This timing is only used by the ergonomics to handle our pause target.</span></span><br><span class="line"> <span class="comment">// It is unclear why this should not include the full pause. We will</span></span><br><span class="line"> <span class="comment">// investigate this in CR 7178365.</span></span><br><span class="line"> <span class="comment">//</span></span><br><span class="line"> <span class="comment">// Preserving the old comment here if that helps the investigation:</span></span><br><span class="line"> <span class="comment">//</span></span><br><span class="line"> <span class="comment">// The elapsed time induced by the start time below deliberately elides</span></span><br><span class="line"> <span class="comment">// the possible verification above.</span></span><br><span class="line"> <span class="keyword">double</span> sample_start_time_sec = os::elapsedTime();</span><br><span class="line"></span><br><span class="line"> g1_policy()->record_collection_pause_start(sample_start_time_sec);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (collector_state()->in_initial_mark_gc()) {</span><br><span class="line"> concurrent_mark()->pre_initial_mark();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> g1_policy()->finalize_collection_set(target_pause_time_ms, &_survivor);</span><br><span class="line"></span><br><span class="line"> evacuation_info.set_collectionset_regions(collection_set()->region_length());</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Make sure the remembered sets are up to date. This needs to be</span></span><br><span class="line"> <span class="comment">// done before register_humongous_regions_with_cset(), because the</span></span><br><span class="line"> <span class="comment">// remembered sets are used there to choose eager reclaim candidates.</span></span><br><span class="line"> <span class="comment">// If the remembered sets are not up to date we might miss some</span></span><br><span class="line"> <span class="comment">// entries that need to be handled.</span></span><br><span class="line"> g1_rem_set()->cleanupHRRS();</span><br><span class="line"></span><br><span class="line"> register_humongous_regions_with_cset();</span><br><span class="line"></span><br><span class="line"> assert(_verifier->check_cset_fast_test(), <span class="string">"Inconsistency in the InCSetState table."</span>);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We call this after finalize_cset() to</span></span><br><span class="line"> <span class="comment">// ensure that the CSet has been finalized.</span></span><br><span class="line"> _cm->verify_no_cset_oops();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (_hr_printer.is_active()) {</span><br><span class="line"> <span class="function">G1PrintCollectionSetClosure <span class="title">cl</span><span class="params">(&_hr_printer)</span></span>;</span><br><span class="line"> _collection_set.iterate(&cl);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Initialize the GC alloc regions.</span></span><br><span class="line"> _allocator->init_gc_alloc_regions(evacuation_info);</span><br><span class="line"></span><br><span class="line"> <span class="function">G1ParScanThreadStateSet <span class="title">per_thread_states</span><span class="params">(<span class="keyword">this</span>, workers()->active_workers(), collection_set()->young_region_length())</span></span>;</span><br><span class="line"> pre_evacuate_collection_set();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Actually do the work...</span></span><br><span class="line"> evacuate_collection_set(&per_thread_states);</span><br><span class="line"></span><br><span class="line"> post_evacuate_collection_set(evacuation_info, &per_thread_states);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">const</span> <span class="keyword">size_t</span>* surviving_young_words = per_thread_states.surviving_young_words();</span><br><span class="line"> free_collection_set(&_collection_set, evacuation_info, surviving_young_words);</span><br><span class="line"></span><br><span class="line"> eagerly_reclaim_humongous_regions();</span><br><span class="line"></span><br><span class="line"> record_obj_copy_mem_stats();</span><br><span class="line"> _survivor_evac_stats.adjust_desired_plab_sz();</span><br><span class="line"> _old_evac_stats.adjust_desired_plab_sz();</span><br><span class="line"></span><br><span class="line"> <span class="keyword">double</span> start = os::elapsedTime();</span><br><span class="line"> start_new_collection_set();</span><br><span class="line"> g1_policy()->phase_times()->record_start_new_cset_time_ms((os::elapsedTime() - start) * <span class="number">1000.0</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (evacuation_failed()) {</span><br><span class="line"> set_used(recalculate_used());</span><br><span class="line"> <span class="keyword">if</span> (_archive_allocator != <span class="literal">NULL</span>) {</span><br><span class="line"> _archive_allocator->clear_used();</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">for</span> (uint i = <span class="number">0</span>; i < ParallelGCThreads; i++) {</span><br><span class="line"> <span class="keyword">if</span> (_evacuation_failed_info_array[i].has_failed()) {</span><br><span class="line"> _gc_tracer_stw->report_evacuation_failed(_evacuation_failed_info_array[i]);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="comment">// The "used" of the the collection set have already been subtracted</span></span><br><span class="line"> <span class="comment">// when they were freed. Add in the bytes evacuated.</span></span><br><span class="line"> increase_used(g1_policy()->bytes_copied_during_gc());</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (collector_state()->in_initial_mark_gc()) {</span><br><span class="line"> <span class="comment">// We have to do this before we notify the CM threads that</span></span><br><span class="line"> <span class="comment">// they can start working to make sure that all the</span></span><br><span class="line"> <span class="comment">// appropriate initialization is done on the CM object.</span></span><br><span class="line"> concurrent_mark()->post_initial_mark();</span><br><span class="line"> <span class="comment">// Note that we don't actually trigger the CM thread at</span></span><br><span class="line"> <span class="comment">// this point. We do that later when we're sure that</span></span><br><span class="line"> <span class="comment">// the current thread has completed its logging output.</span></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> allocate_dummy_regions();</span><br><span class="line"></span><br><span class="line"> _allocator->init_mutator_alloc_region();</span><br><span class="line"></span><br><span class="line"> {</span><br><span class="line"> <span class="keyword">size_t</span> expand_bytes = _heap_sizing_policy->expansion_amount();</span><br><span class="line"> <span class="keyword">if</span> (expand_bytes > <span class="number">0</span>) {</span><br><span class="line"> <span class="keyword">size_t</span> bytes_before = capacity();</span><br><span class="line"> <span class="comment">// No need for an ergo logging here,</span></span><br><span class="line"> <span class="comment">// expansion_amount() does this when it returns a value > 0.</span></span><br><span class="line"> <span class="keyword">double</span> expand_ms;</span><br><span class="line"> <span class="keyword">if</span> (!expand(expand_bytes, _workers, &expand_ms)) {</span><br><span class="line"> <span class="comment">// We failed to expand the heap. Cannot do anything about it.</span></span><br><span class="line"> }</span><br><span class="line"> g1_policy()->phase_times()->record_expand_heap_time(expand_ms);</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We redo the verification but now wrt to the new CSet which</span></span><br><span class="line"> <span class="comment">// has just got initialized after the previous CSet was freed.</span></span><br><span class="line"> _cm->verify_no_cset_oops();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// This timing is only used by the ergonomics to handle our pause target.</span></span><br><span class="line"> <span class="comment">// It is unclear why this should not include the full pause. We will</span></span><br><span class="line"> <span class="comment">// investigate this in CR 7178365.</span></span><br><span class="line"> <span class="keyword">double</span> sample_end_time_sec = os::elapsedTime();</span><br><span class="line"> <span class="keyword">double</span> pause_time_ms = (sample_end_time_sec - sample_start_time_sec) * MILLIUNITS;</span><br><span class="line"> <span class="keyword">size_t</span> total_cards_scanned = g1_policy()->phase_times()->sum_thread_work_items(G1GCPhaseTimes::ScanRS, G1GCPhaseTimes::ScanRSScannedCards);</span><br><span class="line"> g1_policy()->record_collection_pause_end(pause_time_ms, total_cards_scanned, heap_used_bytes_before_gc);</span><br><span class="line"></span><br><span class="line"> evacuation_info.set_collectionset_used_before(collection_set()->bytes_used_before());</span><br><span class="line"> evacuation_info.set_bytes_copied(g1_policy()->bytes_copied_during_gc());</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (VerifyRememberedSets) {</span><br><span class="line"> log_info(gc, verify)(<span class="string">"[Verifying RemSets after GC]"</span>);</span><br><span class="line"> VerifyRegionRemSetClosure v_cl;</span><br><span class="line"> heap_region_iterate(&v_cl);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> _verifier->verify_after_gc(verify_type);</span><br><span class="line"> _verifier->check_bitmaps(<span class="string">"GC End"</span>);</span><br><span class="line"></span><br><span class="line"> assert(!_ref_processor_stw->discovery_enabled(), <span class="string">"Postcondition"</span>);</span><br><span class="line"> _ref_processor_stw->verify_no_references_recorded();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// CM reference discovery will be re-enabled if necessary.</span></span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"><span class="meta">#<span class="meta-keyword">ifdef</span> TRACESPINNING</span></span><br><span class="line"> ParallelTaskTerminator::print_termination_counts();</span><br><span class="line"><span class="meta">#<span class="meta-keyword">endif</span></span></span><br><span class="line"></span><br><span class="line"> gc_epilogue(<span class="literal">false</span>);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Print the remainder of the GC log output.</span></span><br><span class="line"> <span class="keyword">if</span> (evacuation_failed()) {</span><br><span class="line"> log_info(gc)(<span class="string">"To-space exhausted"</span>);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> g1_policy()->print_phases();</span><br><span class="line"> heap_transition.<span class="built_in">print</span>();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// It is not yet to safe to tell the concurrent mark to</span></span><br><span class="line"> <span class="comment">// start as we have some optional output below. We don't want the</span></span><br><span class="line"> <span class="comment">// output from the concurrent mark thread interfering with this</span></span><br><span class="line"> <span class="comment">// logging output either.</span></span><br><span class="line"></span><br><span class="line"> _hrm.verify_optional();</span><br><span class="line"> _verifier->verify_region_sets_optional();</span><br><span class="line"></span><br><span class="line"> TASKQUEUE_STATS_ONLY(print_taskqueue_stats());</span><br><span class="line"> TASKQUEUE_STATS_ONLY(reset_taskqueue_stats());</span><br><span class="line"></span><br><span class="line"> print_heap_after_gc();</span><br><span class="line"> print_heap_regions();</span><br><span class="line"> trace_heap_after_gc(_gc_tracer_stw);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We must call G1MonitoringSupport::update_sizes() in the same scoping level</span></span><br><span class="line"> <span class="comment">// as an active TraceMemoryManagerStats object (i.e. before the destructor for the</span></span><br><span class="line"> <span class="comment">// TraceMemoryManagerStats is called) so that the G1 memory pools are updated</span></span><br><span class="line"> <span class="comment">// before any GC notifications are raised.</span></span><br><span class="line"> g1mm()->update_sizes();</span><br><span class="line"></span><br><span class="line"> _gc_tracer_stw->report_evacuation_info(&evacuation_info);</span><br><span class="line"> _gc_tracer_stw->report_tenuring_threshold(_g1_policy->tenuring_threshold());</span><br><span class="line"> _gc_timer_stw->register_gc_end();</span><br><span class="line"> _gc_tracer_stw->report_gc_end(_gc_timer_stw->gc_end(), _gc_timer_stw->time_partitions());</span><br><span class="line"> }</span><br><span class="line"> <span class="comment">// It should now be safe to tell the concurrent mark thread to start</span></span><br><span class="line"> <span class="comment">// without its logging output interfering with the logging output</span></span><br><span class="line"> <span class="comment">// that came from the pause.</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (should_start_conc_mark) {</span><br><span class="line"> <span class="comment">// CAUTION: after the doConcurrentMark() call below,</span></span><br><span class="line"> <span class="comment">// the concurrent marking thread(s) could be running</span></span><br><span class="line"> <span class="comment">// concurrently with us. Make sure that anything after</span></span><br><span class="line"> <span class="comment">// this point does not assume that we are the only GC thread</span></span><br><span class="line"> <span class="comment">// running. Note: of course, the actual marking work will</span></span><br><span class="line"> <span class="comment">// not start until the safepoint itself is released in</span></span><br><span class="line"> <span class="comment">// SuspendibleThreadSet::desynchronize().</span></span><br><span class="line"> do_concurrent_mark();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> <span class="literal">true</span>;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>往下走就是这一步<code>G1Policy::finalize_collection_set</code>,去处理新生代和老年代</p>
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<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">G1Policy::finalize_collection_set</span><span class="params">(<span class="keyword">double</span> target_pause_time_ms, G1SurvivorRegions* survivor)</span> </span>{</span><br><span class="line"> <span class="keyword">double</span> time_remaining_ms = _collection_set->finalize_young_part(target_pause_time_ms, survivor);</span><br><span class="line"> _collection_set->finalize_old_part(time_remaining_ms);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>这里分别调用了两个方法，可以看到剩余时间是往下传的，来看一下具体的方法</p>
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<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">double</span> <span class="title">G1CollectionSet::finalize_young_part</span><span class="params">(<span class="keyword">double</span> target_pause_time_ms, G1SurvivorRegions* survivors)</span> </span>{</span><br><span class="line"> <span class="keyword">double</span> young_start_time_sec = os::elapsedTime();</span><br><span class="line"></span><br><span class="line"> finalize_incremental_building();</span><br><span class="line"></span><br><span class="line"> guarantee(target_pause_time_ms > <span class="number">0.0</span>,</span><br><span class="line"> <span class="string">"target_pause_time_ms = %1.6lf should be positive"</span>, target_pause_time_ms);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">size_t</span> pending_cards = _policy->pending_cards();</span><br><span class="line"> <span class="keyword">double</span> base_time_ms = _policy->predict_base_elapsed_time_ms(pending_cards);</span><br><span class="line"> <span class="keyword">double</span> time_remaining_ms = MAX2(target_pause_time_ms - base_time_ms, <span class="number">0.0</span>);</span><br><span class="line"></span><br><span class="line"> log_trace(gc, ergo, cset)(<span class="string">"Start choosing CSet. pending cards: "</span> SIZE_FORMAT <span class="string">" predicted base time: %1.2fms remaining time: %1.2fms target pause time: %1.2fms"</span>,</span><br><span class="line"> pending_cards, base_time_ms, time_remaining_ms, target_pause_time_ms);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// The young list is laid with the survivor regions from the previous</span></span><br><span class="line"> <span class="comment">// pause are appended to the RHS of the young list, i.e.</span></span><br><span class="line"> <span class="comment">// [Newly Young Regions ++ Survivors from last pause].</span></span><br><span class="line"></span><br><span class="line"> uint survivor_region_length = survivors->length();</span><br><span class="line"> uint eden_region_length = _g1h->eden_regions_count();</span><br><span class="line"> init_region_lengths(eden_region_length, survivor_region_length);</span><br><span class="line"></span><br><span class="line"> verify_young_cset_indices();</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Clear the fields that point to the survivor list - they are all young now.</span></span><br><span class="line"> survivors->convert_to_eden();</span><br><span class="line"></span><br><span class="line"> _bytes_used_before = _inc_bytes_used_before;</span><br><span class="line"> time_remaining_ms = MAX2(time_remaining_ms - _inc_predicted_elapsed_time_ms, <span class="number">0.0</span>);</span><br><span class="line"></span><br><span class="line"> log_trace(gc, ergo, cset)(<span class="string">"Add young regions to CSet. eden: %u regions, survivors: %u regions, predicted young region time: %1.2fms, target pause time: %1.2fms"</span>,</span><br><span class="line"> eden_region_length, survivor_region_length, _inc_predicted_elapsed_time_ms, target_pause_time_ms);</span><br><span class="line"></span><br><span class="line"> <span class="comment">// The number of recorded young regions is the incremental</span></span><br><span class="line"> <span class="comment">// collection set's current size</span></span><br><span class="line"> set_recorded_rs_lengths(_inc_recorded_rs_lengths);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">double</span> young_end_time_sec = os::elapsedTime();</span><br><span class="line"> phase_times()->record_young_cset_choice_time_ms((young_end_time_sec - young_start_time_sec) * <span class="number">1000.0</span>);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">return</span> time_remaining_ms;</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>下面是老年代的部分</p>
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<figure class="highlight c++"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br></pre></td><td class="code"><pre><span class="line"><span class="function"><span class="keyword">void</span> <span class="title">G1CollectionSet::finalize_old_part</span><span class="params">(<span class="keyword">double</span> time_remaining_ms)</span> </span>{</span><br><span class="line"> <span class="keyword">double</span> non_young_start_time_sec = os::elapsedTime();</span><br><span class="line"> <span class="keyword">double</span> predicted_old_time_ms = <span class="number">0.0</span>;</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (collector_state()->in_mixed_phase()) {</span><br><span class="line"> cset_chooser()->verify();</span><br><span class="line"> <span class="keyword">const</span> uint min_old_cset_length = _policy->calc_min_old_cset_length();</span><br><span class="line"> <span class="keyword">const</span> uint max_old_cset_length = _policy->calc_max_old_cset_length();</span><br><span class="line"></span><br><span class="line"> uint expensive_region_num = <span class="number">0</span>;</span><br><span class="line"> <span class="keyword">bool</span> check_time_remaining = _policy->adaptive_young_list_length();</span><br><span class="line"></span><br><span class="line"> HeapRegion* hr = cset_chooser()-><span class="built_in">peek</span>();</span><br><span class="line"> <span class="keyword">while</span> (hr != <span class="literal">NULL</span>) {</span><br><span class="line"> <span class="keyword">if</span> (old_region_length() >= max_old_cset_length) {</span><br><span class="line"> <span class="comment">// Added maximum number of old regions to the CSet.</span></span><br><span class="line"> log_debug(gc, ergo, cset)(<span class="string">"Finish adding old regions to CSet (old CSet region num reached max). old %u regions, max %u regions"</span>,</span><br><span class="line"> old_region_length(), max_old_cset_length);</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// Stop adding regions if the remaining reclaimable space is</span></span><br><span class="line"> <span class="comment">// not above G1HeapWastePercent.</span></span><br><span class="line"> <span class="keyword">size_t</span> reclaimable_bytes = cset_chooser()->remaining_reclaimable_bytes();</span><br><span class="line"> <span class="keyword">double</span> reclaimable_percent = _policy->reclaimable_bytes_percent(reclaimable_bytes);</span><br><span class="line"> <span class="keyword">double</span> threshold = (<span class="keyword">double</span>) G1HeapWastePercent;</span><br><span class="line"> <span class="keyword">if</span> (reclaimable_percent <= threshold) {</span><br><span class="line"> <span class="comment">// We've added enough old regions that the amount of uncollected</span></span><br><span class="line"> <span class="comment">// reclaimable space is at or below the waste threshold. Stop</span></span><br><span class="line"> <span class="comment">// adding old regions to the CSet.</span></span><br><span class="line"> log_debug(gc, ergo, cset)(<span class="string">"Finish adding old regions to CSet (reclaimable percentage not over threshold). "</span></span><br><span class="line"> <span class="string">"old %u regions, max %u regions, reclaimable: "</span> SIZE_FORMAT <span class="string">"B (%1.2f%%) threshold: "</span> UINTX_FORMAT <span class="string">"%%"</span>,</span><br><span class="line"> old_region_length(), max_old_cset_length, reclaimable_bytes, reclaimable_percent, G1HeapWastePercent);</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">double</span> predicted_time_ms = predict_region_elapsed_time_ms(hr);</span><br><span class="line"> <span class="keyword">if</span> (check_time_remaining) {</span><br><span class="line"> <span class="keyword">if</span> (predicted_time_ms > time_remaining_ms) {</span><br><span class="line"> <span class="comment">// Too expensive for the current CSet.</span></span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (old_region_length() >= min_old_cset_length) {</span><br><span class="line"> <span class="comment">// We have added the minimum number of old regions to the CSet,</span></span><br><span class="line"> <span class="comment">// we are done with this CSet.</span></span><br><span class="line"> log_debug(gc, ergo, cset)(<span class="string">"Finish adding old regions to CSet (predicted time is too high). "</span></span><br><span class="line"> <span class="string">"predicted time: %1.2fms, remaining time: %1.2fms old %u regions, min %u regions"</span>,</span><br><span class="line"> predicted_time_ms, time_remaining_ms, old_region_length(), min_old_cset_length);</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We'll add it anyway given that we haven't reached the</span></span><br><span class="line"> <span class="comment">// minimum number of old regions.</span></span><br><span class="line"> expensive_region_num += <span class="number">1</span>;</span><br><span class="line"> }</span><br><span class="line"> } <span class="keyword">else</span> {</span><br><span class="line"> <span class="keyword">if</span> (old_region_length() >= min_old_cset_length) {</span><br><span class="line"> <span class="comment">// In the non-auto-tuning case, we'll finish adding regions</span></span><br><span class="line"> <span class="comment">// to the CSet if we reach the minimum.</span></span><br><span class="line"></span><br><span class="line"> log_debug(gc, ergo, cset)(<span class="string">"Finish adding old regions to CSet (old CSet region num reached min). old %u regions, min %u regions"</span>,</span><br><span class="line"> old_region_length(), min_old_cset_length);</span><br><span class="line"> <span class="keyword">break</span>;</span><br><span class="line"> }</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="comment">// We will add this region to the CSet.</span></span><br><span class="line"> time_remaining_ms = MAX2(time_remaining_ms - predicted_time_ms, <span class="number">0.0</span>);</span><br><span class="line"> predicted_old_time_ms += predicted_time_ms;</span><br><span class="line"> cset_chooser()->pop(); <span class="comment">// already have region via peek()</span></span><br><span class="line"> _g1h->old_set_remove(hr);</span><br><span class="line"> add_old_region(hr);</span><br><span class="line"></span><br><span class="line"> hr = cset_chooser()-><span class="built_in">peek</span>();</span><br><span class="line"> }</span><br><span class="line"> <span class="keyword">if</span> (hr == <span class="literal">NULL</span>) {</span><br><span class="line"> log_debug(gc, ergo, cset)(<span class="string">"Finish adding old regions to CSet (candidate old regions not available)"</span>);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> <span class="keyword">if</span> (expensive_region_num > <span class="number">0</span>) {</span><br><span class="line"> <span class="comment">// We print the information once here at the end, predicated on</span></span><br><span class="line"> <span class="comment">// whether we added any apparently expensive regions or not, to</span></span><br><span class="line"> <span class="comment">// avoid generating output per region.</span></span><br><span class="line"> log_debug(gc, ergo, cset)(<span class="string">"Added expensive regions to CSet (old CSet region num not reached min)."</span></span><br><span class="line"> <span class="string">"old: %u regions, expensive: %u regions, min: %u regions, remaining time: %1.2fms"</span>,</span><br><span class="line"> old_region_length(), expensive_region_num, min_old_cset_length, time_remaining_ms);</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> cset_chooser()->verify();</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line"> stop_incremental_building();</span><br><span class="line"></span><br><span class="line"> log_debug(gc, ergo, cset)(<span class="string">"Finish choosing CSet. old: %u regions, predicted old region time: %1.2fms, time remaining: %1.2f"</span>,</span><br><span class="line"> old_region_length(), predicted_old_time_ms, time_remaining_ms);</span><br><span class="line"></span><br><span class="line"> <span class="keyword">double</span> non_young_end_time_sec = os::elapsedTime();</span><br><span class="line"> phase_times()->record_non_young_cset_choice_time_ms((non_young_end_time_sec - non_young_start_time_sec) * <span class="number">1000.0</span>);</span><br><span class="line"></span><br><span class="line"> QuickSort::sort(_collection_set_regions, _collection_set_cur_length, compare_region_idx, <span class="literal">true</span>);</span><br><span class="line">}</span><br></pre></td></tr></table></figure>
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<p>上面第三行是个判断，当前是否是 mixed 回收阶段，如果不是的话其实是没有老年代什么事的，所以可以看到代码基本是从这个 if 判断<br><code>if (collector_state()->in_mixed_phase()) {</code>开始往下走的<br>先写到这，偏向于做笔记用，有错轻拍</p>
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href="/tags/%E7%B3%9F%E5%BF%83%E4%BA%8B/" rel="tag">糟心事</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E7%B4%A2%E5%BC%95/" rel="tag">索引</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E7%BC%93%E5%AD%98/" rel="tag">缓存</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E7%BE%8E%E5%9B%BD/" rel="tag">美国</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%87%AA%E9%80%82%E5%BA%94%E6%8B%93%E5%B1%95/" rel="tag">自适应拓展</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%A7%84%E5%88%99/" rel="tag">规则</a><span class="tag-list-count">1</span></li><li class="tag-list-item"><a class="tag-list-link" href="/tags/%E8%AE%BE%E8%AE%A1%E6%A8%A1%E5%BC%8F/" rel="tag">设计模式</a><span 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