jvm源码解读--14 defNewGeneration.cpp gc标记复制之后,进行空间清理
进入Eden()->clean()函数
void EdenSpace::clear(bool mangle_space) { ContiguousSpace::clear(mangle_space); set_soft_end(end()); }
进入
void ContiguousSpace::clear(bool mangle_space) { set_top(bottom()); set_saved_mark(); CompactibleSpace::clear(mangle_space); }
打印对象,这个是eden
(gdb) p this $154 = (EdenSpace * const) 0x7f4780020328 (gdb) p * this $155 = (EdenSpace) { <ContiguousSpace> = { <CompactibleSpace> = { <Space> = { <CHeapObj<1280u>> = { <AllocatedObj> = { _vptr.AllocatedObj = 0x7f4788515a90 <vtable for EdenSpace+16> }, <No data fields>}, members of Space: _bottom = 0xf3800000, _end = 0xf5600000, _saved_mark_word = 0xf4dccdb8, _preconsumptionDirtyCardClosure = 0x0, _par_seq_tasks = { <StackObj> = { <AllocatedObj> = { _vptr.AllocatedObj = 0x7f47884fb650 <vtable for SequentialSubTasksDone+16> }, <No data fields>}, members of SequentialSubTasksDone: _n_tasks = 0, _n_claimed = 0, _n_threads = 0, _n_completed = 0 } }, members of CompactibleSpace: _compaction_top = 0xf3800000, _next_compaction_space = 0x7f4780020438, _first_dead = 0xf1f1f1f1f1f1f1f1, _end_of_live = 0xf1f1f1f1f1f1f1f1 }, members of ContiguousSpace: _top = 0xf4dccdb8, _concurrent_iteration_safe_limit = 0xf3800000, _mangler = 0x7f47800203e8 }, members of EdenSpace: _gen = 0x7f478001f1c8, _soft_end = 0xf5600000 }
看实现
(gdb) p bottom() $156 = (HeapWord *) 0xf3800000 (gdb) p top() $157 = (HeapWord *) 0xf4dccdb8
将top清空
设置mark
virtual void set_saved_mark() { _saved_mark_word = top(); }
清理完之后的对象
(gdb) p *this $159 = (EdenSpace) { <ContiguousSpace> = { <CompactibleSpace> = { <Space> = { <CHeapObj<1280u>> = { <AllocatedObj> = { _vptr.AllocatedObj = 0x7f4788515a90 <vtable for EdenSpace+16> }, <No data fields>}, members of Space: _bottom = 0xf3800000, _end = 0xf5600000, _saved_mark_word = 0xf3800000, _preconsumptionDirtyCardClosure = 0x0, _par_seq_tasks = { <StackObj> = { <AllocatedObj> = { _vptr.AllocatedObj = 0x7f47884fb650 <vtable for SequentialSubTasksDone+16> }, <No data fields>}, members of SequentialSubTasksDone: _n_tasks = 0, _n_claimed = 0, _n_threads = 0, _n_completed = 0 } }, members of CompactibleSpace: _compaction_top = 0xf3800000, _next_compaction_space = 0x7f4780020438, _first_dead = 0xf1f1f1f1f1f1f1f1, _end_of_live = 0xf1f1f1f1f1f1f1f1 }, members of ContiguousSpace: _top = 0xf3800000, _concurrent_iteration_safe_limit = 0xf3800000, _mangler = 0x7f47800203e8 }, members of EdenSpace: _gen = 0x7f478001f1c8, _soft_end = 0xf5600000 }
接着看
CompactibleSpace::clear(mangle_space); ---------------------------------------------- void CompactibleSpace::clear(bool mangle_space) { Space::clear(mangle_space); _compaction_top = bottom(); } ---------------------------------------------- void Space::clear(bool mangle_space) { if (ZapUnusedHeapArea && mangle_space) { mangle_unused_area(); } } ------------------------------------------------- void ContiguousSpace::mangle_unused_area() { mangler()->mangle_unused_area(); } ----------------------------------------------------- void SpaceMangler::mangle_unused_area() { assert(ZapUnusedHeapArea, "Mangling should not be in use"); // Mangle between top and the high water mark. Safeguard // against the space changing since top_for_allocations was // set. HeapWord* mangled_end = MIN2(top_for_allocations(), end()); if (top() < mangled_end) { MemRegion mangle_mr(top(), mangled_end); SpaceMangler::mangle_region(mangle_mr); // Light weight check of mangling. check_mangled_unused_area(end()); } // Complete check of unused area which is functional when // DEBUG_MANGLING is defined. check_mangled_unused_area_complete(); }
打印这个spaceMangler对象
(gdb) p _mangler $162 = (GenSpaceMangler *) 0x7f47800203e8 (gdb) p *_mangler $163 = (GenSpaceMangler) { <SpaceMangler> = { <CHeapObj<1280u>> = { <AllocatedObj> = { _vptr.AllocatedObj = 0x7f47885163d0 <vtable for GenSpaceMangler+16> }, <No data fields>}, members of SpaceMangler: _top_for_allocations = 0xf4dccdb8 }, members of GenSpaceMangler: _sp = 0x7f4780020328 }
查看紫色函数
(gdb) p end() $164 = (HeapWord *) 0xf5600000 (gdb) p _top_for_allocations $165 = (HeapWord *) 0xf4dccdb8
进入棕色函数
// Simply mangle the MemRegion mr. void SpaceMangler::mangle_region(MemRegion mr) { assert(ZapUnusedHeapArea, "Mangling should not be in use"); #ifdef ASSERT if(TraceZapUnusedHeapArea) { gclog_or_tty->print("Mangling [0x%x to 0x%x)", mr.start(), mr.end()); } Copy::fill_to_words(mr.start(), mr.word_size(), badHeapWord); if(TraceZapUnusedHeapArea) { gclog_or_tty->print_cr(" done"); } #endif }
进入函数
// Fill methods // Fill word-aligned words, not atomic on each word // set_words static void fill_to_words(HeapWord* to, size_t count, juint value = 0) { assert_params_ok(to, LogHeapWordSize); pd_fill_to_words(to, count, value); }
进入
static void pd_fill_to_words(HeapWord* tohw, size_t count, juint value) { #ifdef AMD64 julong* to = (julong*) tohw; julong v = ((julong) value << 32) | value; while (count-- > 0) { *to++ = v; } #else..无用.. #endif // AMD64 }
看badHeapWord的值
(gdb) p/x value $171 = 0xbaadbabe
那么上述过程就是将heap的值全部设置成了0xbaadbabe
接着就是对from区域
(gdb) p from() $175 = (ContiguousSpace *) 0x7f4780020438
重要的交换空间
swap_spaces();
交换之前
(gdb) p this $181 = (DefNewGeneration * const) 0x7f478001f1c8 (gdb) p* this $182 = (DefNewGeneration) { <Generation> = { <CHeapObj<1280u>> = { <AllocatedObj> = { _vptr.AllocatedObj = 0x7f47884ff590 <vtable for DefNewGeneration+16> }, <No data fields>}, members of Generation: _time_of_last_gc = -1012762419733073423, _prev_used_region = { _start = 0x0, _word_size = 0 }, _reserved = { _start = 0xf3800000, _word_size = 6553600 }, ....略部分 _promo_failure_drain_in_progress = false, _gen_counters = 0x7f4780020638, _eden_counters = 0x7f478000d678, _from_counters = 0x7f4780021888, _to_counters = 0x7f4780021d78, _max_eden_size = 31457280, _max_survivor_size = 10485760, _should_allocate_from_space = false, _eden_space = 0x7f4780020328, _from_space = 0x7f4780020438, _to_space = 0x7f4780020538, _gc_timer = 0x7f4780022268 }
代码为
void DefNewGeneration::swap_spaces() { ContiguousSpace* s = from(); _from_space = to(); _to_space = s; eden()->set_next_compaction_space(from()); // The to-space is normally empty before a compaction so need // not be considered. The exception is during promotion // failure handling when to-space can contain live objects. from()->set_next_compaction_space(NULL); if (UsePerfData) { CSpaceCounters* c = _from_counters; _from_counters = _to_counters; _to_counters = c; } }
这个函数为 eden()->set_next_compaction_space(from());
void set_next_compaction_space(CompactibleSpace* csp) { _next_compaction_space = csp; }
将eden()的值设置为新的from值,(即原来的from空间已经变为了to空间)
if (UsePerfData) { CSpaceCounters* c = _from_counters; _from_counters = _to_counters; _to_counters = c; }
设置完成后就结束了
