Java 方法直接调用 vs 单元素循环调用
Java method direct invocation vs single element loop invocation
最近我想看看直接在一个对象上调用一个方法与在同一个对象上调用相同的方法有什么性能差异，如果对象被添加到单个元素 ArrayList 中，我们尝试循环那个元素列表。
老实说，我的假设是差异很小，因为我希望展开单个元素循环，因此调用模仿直接调用。
为了测试我创建了以下简单的 JMH 示例：https://gist.github.com/nikkatsa/69a58c63c1b79b245d700f6465bce7f7
令我惊讶的是，直接在元素上调用该方法似乎快了约 2.5 倍。这是一个很大的数字，因为我的期望完全不同：
Benchmark Mode Cnt Score Error Units
SingleElementLoopBenchmark.directInvocation thrpt 10 332576972.176 ± 2740616.755 ops/s
SingleElementLoopBenchmark.singleElementLoopInvocation thrpt 10 130179329.978 ± 1303776.248 ops/s
我在推特上发了一些帖子，希望得到一些指导来理解为什么会这样。有人告诉我 运行ning perf 会给我一个线索。所以我用 -perf dtraceasm 做了 运行，我得到了以下两个输出，第一个用于直接调用，第二个用于循环调用：
....[Hottest Region 1]..............................................................................
c2, com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub, version 115 (69 bytes)
0x000000010b73c92c: mov %rbp,%r9
0x000000010b73c92f: movzbl 0x94(%r9),%r10d ;*getfield isDone {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@27 (line 123)
; implicit exception: dispatches to 0x000000010b73ca5e
0x000000010b73c937: test %r10d,%r10d
0x000000010b73c93a: jne 0x000000010b73c9da ;*ifeq {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@30 (line 123)
0x000000010b73c940: mov [=12=]x1,%ebp
0x000000010b73c945: data16 data16 nopw 0x0(%rax,%rax,1) ;*aload_1 {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@33 (line 124)
9.56% ↗ 0x000000010b73c950: mov 0x40(%rsp),%r10
1.00% │ 0x000000010b73c955: mov 0xc(%r10),%r10d ;*getfield dispatcher {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::directInvocation@1 (line 23)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@17 (line 121)
0.17% │ 0x000000010b73c959: mov 0xc(%r12,%r10,8),%r11d ; implicit exception: dispatches to 0x000000010b73ca12
11.18% │ 0x000000010b73c95e: test %r11d,%r11d
0.00% │ 0x000000010b73c961: je 0x000000010b73c9c9 ;*invokevirtual performAction {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invoke@5 (line 40)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::directInvocation@5 (line 23)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@17 (line 121)
10.69% │ 0x000000010b73c963: mov %r9,(%rsp)
0.65% │ 0x000000010b73c967: mov 0x38(%rsp),%rsi
0.00% │ 0x000000010b73c96c: mov [=12=]x1,%edx
0.14% │ 0x000000010b73c971: xchg %ax,%ax
10.08% │ 0x000000010b73c973: callq 0x000000010b6c2900 ; ImmutableOopMap{[48]=Oop [56]=Oop [64]=Oop [0]=Oop }
│ ;*invokevirtual consume {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Listener::performAction@2 (line 53)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invoke@5 (line 40)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::directInvocation@5 (line 23)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@17 (line 121)
│ ; {optimized virtual_call}
1.44% │ 0x000000010b73c978: mov (%rsp),%r9
0.19% │ 0x000000010b73c97c: movzbl 0x94(%r9),%r8d ;*ifeq {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@30 (line 123)
9.77% │ 0x000000010b73c984: mov 0x108(%r15),%r10
0.99% │ 0x000000010b73c98b: add [=12=]x1,%rbp ; ImmutableOopMap{r9=Oop [48]=Oop [56]=Oop [64]=Oop }
│ ;*ifeq {reexecute=1 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@30 (line 123)
0.02% │ 0x000000010b73c98f: test %eax,(%r10) ; {poll}
0.28% │ 0x000000010b73c992: test %r8d,%r8d
0.00% ╰ 0x000000010b73c995: je 0x000000010b73c950 ;*aload_1 {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@33 (line 124)
0x000000010b73c997: movabs [=12=]x10abd7d62,%r10
0x000000010b73c9a1: callq *%r10 ;*invokestatic nanoTime {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@34 (line 124)
0x000000010b73c9a4: mov 0x30(%rsp),%r10
0x000000010b73c9a9: mov %rbp,0x18(%r10) ;*putfield measuredOps {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@49 (line 126)
0x000000010b73c9ad: mov %rax,0x30(%r10) ;*putfield stopTime {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@37 (line 124)
0x000000010b73c9b1: movq [=12=]x0,0x20(%r10) ;*invokevirtual directInvocation {reexecute=0 rethrow=0 return_oop=0}
....................................................................................................
....[Hottest Region 1]..............................................................................
c2, com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub, version 115 (279 bytes)
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@27 (line 123)
; implicit exception: dispatches to 0x000000011153fffe
0x000000011153fa81: test %r10d,%r10d
0x000000011153fa84: jne 0x000000011153fbe4 ;*ifeq {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@30 (line 123)
0x000000011153fa8a: mov 0x58(%rsp),%rdx
0x000000011153fa8f: test %rdx,%rdx
0x000000011153fa92: je 0x000000011153fd5e
0x000000011153fa98: mov [=13=]x1,%ebx
╭ 0x000000011153fa9d: jmp 0x000000011153fad6
0.19% │ ↗ 0x000000011153fa9f: mov 0x58(%rsp),%r13
3.55% │ │ 0x000000011153faa4: mov (%rsp),%rcx
0.09% │ │ 0x000000011153faa8: mov 0x60(%rsp),%rdx
0.22% │ │ 0x000000011153faad: mov 0x50(%rsp),%r11
0.17% │ │ 0x000000011153fab2: mov 0x8(%rsp),%rbx ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0}
│ │ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@12 (line 44)
│ │ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ │ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
3.55% │↗│ 0x000000011153fab7: movzbl 0x94(%r11),%r8d ;*goto {reexecute=0 rethrow=0 return_oop=0}
│││ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@35 (line 44)
│││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.16% │││ 0x000000011153fabf: mov 0x108(%r15),%r10
0.28% │││ 0x000000011153fac6: add [=13=]x1,%rbx ; ImmutableOopMap{r11=Oop rcx=Oop rdx=Oop r13=Oop }
│││ ;*ifeq {reexecute=1 rethrow=0 return_oop=0}
│││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@30 (line 123)
0.19% │││ 0x000000011153faca: test %eax,(%r10) ; {poll}
4.00% │││ 0x000000011153facd: test %r8d,%r8d
│││ 0x000000011153fad0: jne 0x000000011153fbe9 ;*aload_1 {reexecute=0 rethrow=0 return_oop=0}
│││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@33 (line 124)
0.07% ↘││ 0x000000011153fad6: mov 0xc(%rcx),%r8d ;*getfield dispatcher {reexecute=0 rethrow=0 return_oop=0}
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@1 (line 28)
││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.22% ││ 0x000000011153fada: mov 0x10(%r12,%r8,8),%r10d ;*getfield singleListenerList {reexecute=0 rethrow=0 return_oop=0}
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@4 (line 44)
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
││ ; implicit exception: dispatches to 0x000000011153ff2a
0.21% ││ 0x000000011153fadf: mov 0x8(%r12,%r10,8),%edi ; implicit exception: dispatches to 0x000000011153ff3e
4.39% ││ 0x000000011153fae4: cmp [=13=]x237565,%edi ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Dispatcher')}
││ 0x000000011153faea: jne 0x000000011153fc92
0.33% ││ 0x000000011153faf0: lea (%r12,%r10,8),%r9 ;*invokeinterface size {reexecute=0 rethrow=0 return_oop=0}
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@7 (line 44)
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.09% ││ 0x000000011153faf4: mov 0x10(%r9),%r9d
0.14% ││ 0x000000011153faf8: test %r9d,%r9d
╰│ 0x000000011153fafb: jle 0x000000011153fab7 ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@12 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
3.98% │ 0x000000011153fafd: lea (%r12,%r8,8),%rdi ;*getfield dispatcher {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@1 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.06% │ 0x000000011153fb01: xor %r9d,%r9d ;*aload_0 {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@15 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.09% │ 0x000000011153fb04: mov 0x8(%r12,%r10,8),%esi ; implicit exception: dispatches to 0x000000011153ff4e
0.06% │ 0x000000011153fb09: cmp [=13=]x237565,%esi ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Dispatcher')}
0.00% │ 0x000000011153fb0f: jne 0x000000011153fcc2
3.93% │ 0x000000011153fb15: lea (%r12,%r10,8),%rax ;*invokeinterface get {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.06% │ 0x000000011153fb19: mov 0x10(%rax),%r10d ;*getfield size {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.ArrayList::get@2 (line 458)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.11% │ 0x000000011153fb1d: test %r10d,%r10d
│ 0x000000011153fb20: jl 0x000000011153fcf6 ;*invokestatic checkIndex {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.Objects::checkIndex@3 (line 372)
│ ; - java.util.ArrayList::get@5 (line 458)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.28% │ 0x000000011153fb26: cmp %r10d,%r9d
0.00% │ 0x000000011153fb29: jae 0x000000011153fc1c
3.97% │ 0x000000011153fb2f: mov 0x14(%rax),%r10d ;*getfield elementData {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.ArrayList::elementData@1 (line 442)
│ ; - java.util.ArrayList::get@11 (line 459)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.05% │ 0x000000011153fb33: mov %r9d,%ebp ;*invokestatic checkIndex {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.Objects::checkIndex@3 (line 372)
│ ; - java.util.ArrayList::get@5 (line 458)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.08% │ 0x000000011153fb36: mov 0xc(%r12,%r10,8),%esi ; implicit exception: dispatches to 0x000000011153ff62
1.27% │ 0x000000011153fb3b: cmp %esi,%ebp
│ 0x000000011153fb3d: jae 0x000000011153fc5a
3.94% │ 0x000000011153fb43: shl [=13=]x3,%r10
0.05% │ 0x000000011153fb47: mov 0x10(%r10,%rbp,4),%r9d ;*aaload {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.ArrayList::elementData@5 (line 442)
│ ; - java.util.ArrayList::get@11 (line 459)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
1.71% │ 0x000000011153fb4c: mov 0x8(%r12,%r9,8),%r10d ; implicit exception: dispatches to 0x000000011153ff72
17.85% │ 0x000000011153fb51: cmp [=13=]x237522,%r10d ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Listener')}
0.00% │ 0x000000011153fb58: jne 0x000000011153fef6 ;*checkcast {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@25 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
3.79% │ 0x000000011153fb5e: mov %rdi,0x18(%rsp)
0.02% │ 0x000000011153fb63: mov %r8d,0x10(%rsp)
0.02% │ 0x000000011153fb68: mov %rbx,0x8(%rsp)
0.19% │ 0x000000011153fb6d: mov %r11,0x50(%rsp)
3.95% │ 0x000000011153fb72: mov %rdx,0x60(%rsp)
0.02% │ 0x000000011153fb77: mov %rcx,(%rsp)
0.03% │ 0x000000011153fb7b: mov %r13,0x58(%rsp)
0.36% │ 0x000000011153fb80: mov %rdx,%rsi
3.78% │ 0x000000011153fb83: mov [=13=]x1,%edx
0.01% │ 0x000000011153fb88: vzeroupper
4.05% │ 0x000000011153fb8b: callq 0x00000001114c2900 ; ImmutableOopMap{[80]=Oop [88]=Oop [96]=Oop [0]=Oop [16]=NarrowOop [24]=Oop }
│ ;*invokevirtual consume {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Listener::performAction@2 (line 53)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@29 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
│ ; {optimized virtual_call}
0.98% │ 0x000000011153fb90: mov 0x10(%rsp),%r8d
3.61% │ 0x000000011153fb95: mov 0x10(%r12,%r8,8),%r10d ;*getfield singleListenerList {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@4 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.24% │ 0x000000011153fb9a: mov 0x8(%r12,%r10,8),%r9d ; implicit exception: dispatches to 0x000000011153ff9e
0.74% │ 0x000000011153fb9f: inc %ebp ;*iinc {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@32 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.04% │ 0x000000011153fba1: cmp [=13=]x237565,%r9d ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Dispatcher')}
0.00% │ 0x000000011153fba8: jne 0x000000011153fd36
3.60% │ 0x000000011153fbae: lea (%r12,%r10,8),%r11 ;*invokeinterface size {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@7 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.11% │ 0x000000011153fbb2: mov 0x10(%r11),%r9d
0.35% │ 0x000000011153fbb6: cmp %r9d,%ebp
╰ 0x000000011153fbb9: jge 0x000000011153fa9f ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@12 (line 44)
; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0x000000011153fbbf: mov %ebp,%r9d
0x000000011153fbc2: mov 0x58(%rsp),%r13
0x000000011153fbc7: mov (%rsp),%rcx
0x000000011153fbcb: mov 0x60(%rsp),%rdx
0x000000011153fbd0: mov 0x50(%rsp),%r11
0x000000011153fbd5: mov 0x8(%rsp),%rbx
....................................................................................................
如果可能的话，我想要一些帮助来理解上面的两个输出。从我的理解来看，似乎在循环时，程序付出了相当大的代价来检查数组列表的大小以执行循环以及将对象转换为适当类型的成本，这是由于列表泛型.我无法真正理解循环是否展开，但我相信它会展开？
如果有人理解上面的输出并能给出一些指示来说明正在发生的事情，我们将不胜感激。
您衡量一个几乎什么都不做的操作与一个至少涉及四个相关内存加载的操作：
- ArrayList.size
- ArrayList.elementData
- elementData.length
- 元素数据[0]
再加上至少一次边界检查。我说 "at least"，因为这是最好的优化编译器可能做的事情。然而，HotSpot 执行两个绑定检查：一个在 ArrayList.get() 中，另一个用于 elementData 数组访问。
此外，ArrayList 包含一个对象数组，因此为了从列表中获取 Listener 的实例，需要将对象转换为目标类型。这是一个额外的内存负载加上类型检查。
从不同的角度看基准分数：单个元素列表不是慢 2.5 倍，而是长 3 纳秒：
Benchmark Mode Cnt Score Error Units
SingleElementLoopBenchmark.directInvocation avgt 5 2,340 ± 0,095 ns/op
SingleElementLoopBenchmark.singleElementLoopInvocation avgt 5 5,283 ± 0,074 ns/op
3 纳秒！ 这只是 2 GHz 内核的 6 CPU 个周期。光可以在 3 纳秒内传播不到 1 米。您真的期望 ArrayList 的开销比这少吗？不管开销多低，如果和完全没有开销相比，比例可以无限大。
最近我想看看直接在一个对象上调用一个方法与在同一个对象上调用相同的方法有什么性能差异，如果对象被添加到单个元素 ArrayList 中，我们尝试循环那个元素列表。
老实说，我的假设是差异很小，因为我希望展开单个元素循环，因此调用模仿直接调用。
为了测试我创建了以下简单的 JMH 示例：https://gist.github.com/nikkatsa/69a58c63c1b79b245d700f6465bce7f7
令我惊讶的是，直接在元素上调用该方法似乎快了约 2.5 倍。这是一个很大的数字，因为我的期望完全不同：
Benchmark Mode Cnt Score Error Units
SingleElementLoopBenchmark.directInvocation thrpt 10 332576972.176 ± 2740616.755 ops/s
SingleElementLoopBenchmark.singleElementLoopInvocation thrpt 10 130179329.978 ± 1303776.248 ops/s
我在推特上发了一些帖子，希望得到一些指导来理解为什么会这样。有人告诉我 运行ning perf 会给我一个线索。所以我用 -perf dtraceasm 做了 运行，我得到了以下两个输出，第一个用于直接调用，第二个用于循环调用：
....[Hottest Region 1]..............................................................................
c2, com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub, version 115 (69 bytes)
0x000000010b73c92c: mov %rbp,%r9
0x000000010b73c92f: movzbl 0x94(%r9),%r10d ;*getfield isDone {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@27 (line 123)
; implicit exception: dispatches to 0x000000010b73ca5e
0x000000010b73c937: test %r10d,%r10d
0x000000010b73c93a: jne 0x000000010b73c9da ;*ifeq {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@30 (line 123)
0x000000010b73c940: mov [=12=]x1,%ebp
0x000000010b73c945: data16 data16 nopw 0x0(%rax,%rax,1) ;*aload_1 {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@33 (line 124)
9.56% ↗ 0x000000010b73c950: mov 0x40(%rsp),%r10
1.00% │ 0x000000010b73c955: mov 0xc(%r10),%r10d ;*getfield dispatcher {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::directInvocation@1 (line 23)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@17 (line 121)
0.17% │ 0x000000010b73c959: mov 0xc(%r12,%r10,8),%r11d ; implicit exception: dispatches to 0x000000010b73ca12
11.18% │ 0x000000010b73c95e: test %r11d,%r11d
0.00% │ 0x000000010b73c961: je 0x000000010b73c9c9 ;*invokevirtual performAction {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invoke@5 (line 40)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::directInvocation@5 (line 23)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@17 (line 121)
10.69% │ 0x000000010b73c963: mov %r9,(%rsp)
0.65% │ 0x000000010b73c967: mov 0x38(%rsp),%rsi
0.00% │ 0x000000010b73c96c: mov [=12=]x1,%edx
0.14% │ 0x000000010b73c971: xchg %ax,%ax
10.08% │ 0x000000010b73c973: callq 0x000000010b6c2900 ; ImmutableOopMap{[48]=Oop [56]=Oop [64]=Oop [0]=Oop }
│ ;*invokevirtual consume {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Listener::performAction@2 (line 53)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invoke@5 (line 40)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::directInvocation@5 (line 23)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@17 (line 121)
│ ; {optimized virtual_call}
1.44% │ 0x000000010b73c978: mov (%rsp),%r9
0.19% │ 0x000000010b73c97c: movzbl 0x94(%r9),%r8d ;*ifeq {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@30 (line 123)
9.77% │ 0x000000010b73c984: mov 0x108(%r15),%r10
0.99% │ 0x000000010b73c98b: add [=12=]x1,%rbp ; ImmutableOopMap{r9=Oop [48]=Oop [56]=Oop [64]=Oop }
│ ;*ifeq {reexecute=1 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@30 (line 123)
0.02% │ 0x000000010b73c98f: test %eax,(%r10) ; {poll}
0.28% │ 0x000000010b73c992: test %r8d,%r8d
0.00% ╰ 0x000000010b73c995: je 0x000000010b73c950 ;*aload_1 {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@33 (line 124)
0x000000010b73c997: movabs [=12=]x10abd7d62,%r10
0x000000010b73c9a1: callq *%r10 ;*invokestatic nanoTime {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@34 (line 124)
0x000000010b73c9a4: mov 0x30(%rsp),%r10
0x000000010b73c9a9: mov %rbp,0x18(%r10) ;*putfield measuredOps {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@49 (line 126)
0x000000010b73c9ad: mov %rax,0x30(%r10) ;*putfield stopTime {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_directInvocation_jmhTest::directInvocation_thrpt_jmhStub@37 (line 124)
0x000000010b73c9b1: movq [=12=]x0,0x20(%r10) ;*invokevirtual directInvocation {reexecute=0 rethrow=0 return_oop=0}
....................................................................................................
....[Hottest Region 1]..............................................................................
c2, com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub, version 115 (279 bytes)
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@27 (line 123)
; implicit exception: dispatches to 0x000000011153fffe
0x000000011153fa81: test %r10d,%r10d
0x000000011153fa84: jne 0x000000011153fbe4 ;*ifeq {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@30 (line 123)
0x000000011153fa8a: mov 0x58(%rsp),%rdx
0x000000011153fa8f: test %rdx,%rdx
0x000000011153fa92: je 0x000000011153fd5e
0x000000011153fa98: mov [=13=]x1,%ebx
╭ 0x000000011153fa9d: jmp 0x000000011153fad6
0.19% │ ↗ 0x000000011153fa9f: mov 0x58(%rsp),%r13
3.55% │ │ 0x000000011153faa4: mov (%rsp),%rcx
0.09% │ │ 0x000000011153faa8: mov 0x60(%rsp),%rdx
0.22% │ │ 0x000000011153faad: mov 0x50(%rsp),%r11
0.17% │ │ 0x000000011153fab2: mov 0x8(%rsp),%rbx ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0}
│ │ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@12 (line 44)
│ │ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ │ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
3.55% │↗│ 0x000000011153fab7: movzbl 0x94(%r11),%r8d ;*goto {reexecute=0 rethrow=0 return_oop=0}
│││ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@35 (line 44)
│││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.16% │││ 0x000000011153fabf: mov 0x108(%r15),%r10
0.28% │││ 0x000000011153fac6: add [=13=]x1,%rbx ; ImmutableOopMap{r11=Oop rcx=Oop rdx=Oop r13=Oop }
│││ ;*ifeq {reexecute=1 rethrow=0 return_oop=0}
│││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@30 (line 123)
0.19% │││ 0x000000011153faca: test %eax,(%r10) ; {poll}
4.00% │││ 0x000000011153facd: test %r8d,%r8d
│││ 0x000000011153fad0: jne 0x000000011153fbe9 ;*aload_1 {reexecute=0 rethrow=0 return_oop=0}
│││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@33 (line 124)
0.07% ↘││ 0x000000011153fad6: mov 0xc(%rcx),%r8d ;*getfield dispatcher {reexecute=0 rethrow=0 return_oop=0}
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@1 (line 28)
││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.22% ││ 0x000000011153fada: mov 0x10(%r12,%r8,8),%r10d ;*getfield singleListenerList {reexecute=0 rethrow=0 return_oop=0}
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@4 (line 44)
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
││ ; implicit exception: dispatches to 0x000000011153ff2a
0.21% ││ 0x000000011153fadf: mov 0x8(%r12,%r10,8),%edi ; implicit exception: dispatches to 0x000000011153ff3e
4.39% ││ 0x000000011153fae4: cmp [=13=]x237565,%edi ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Dispatcher')}
││ 0x000000011153faea: jne 0x000000011153fc92
0.33% ││ 0x000000011153faf0: lea (%r12,%r10,8),%r9 ;*invokeinterface size {reexecute=0 rethrow=0 return_oop=0}
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@7 (line 44)
││ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
││ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.09% ││ 0x000000011153faf4: mov 0x10(%r9),%r9d
0.14% ││ 0x000000011153faf8: test %r9d,%r9d
╰│ 0x000000011153fafb: jle 0x000000011153fab7 ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@12 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
3.98% │ 0x000000011153fafd: lea (%r12,%r8,8),%rdi ;*getfield dispatcher {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@1 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.06% │ 0x000000011153fb01: xor %r9d,%r9d ;*aload_0 {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@15 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.09% │ 0x000000011153fb04: mov 0x8(%r12,%r10,8),%esi ; implicit exception: dispatches to 0x000000011153ff4e
0.06% │ 0x000000011153fb09: cmp [=13=]x237565,%esi ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Dispatcher')}
0.00% │ 0x000000011153fb0f: jne 0x000000011153fcc2
3.93% │ 0x000000011153fb15: lea (%r12,%r10,8),%rax ;*invokeinterface get {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.06% │ 0x000000011153fb19: mov 0x10(%rax),%r10d ;*getfield size {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.ArrayList::get@2 (line 458)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.11% │ 0x000000011153fb1d: test %r10d,%r10d
│ 0x000000011153fb20: jl 0x000000011153fcf6 ;*invokestatic checkIndex {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.Objects::checkIndex@3 (line 372)
│ ; - java.util.ArrayList::get@5 (line 458)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.28% │ 0x000000011153fb26: cmp %r10d,%r9d
0.00% │ 0x000000011153fb29: jae 0x000000011153fc1c
3.97% │ 0x000000011153fb2f: mov 0x14(%rax),%r10d ;*getfield elementData {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.ArrayList::elementData@1 (line 442)
│ ; - java.util.ArrayList::get@11 (line 459)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.05% │ 0x000000011153fb33: mov %r9d,%ebp ;*invokestatic checkIndex {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.Objects::checkIndex@3 (line 372)
│ ; - java.util.ArrayList::get@5 (line 458)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.08% │ 0x000000011153fb36: mov 0xc(%r12,%r10,8),%esi ; implicit exception: dispatches to 0x000000011153ff62
1.27% │ 0x000000011153fb3b: cmp %esi,%ebp
│ 0x000000011153fb3d: jae 0x000000011153fc5a
3.94% │ 0x000000011153fb43: shl [=13=]x3,%r10
0.05% │ 0x000000011153fb47: mov 0x10(%r10,%rbp,4),%r9d ;*aaload {reexecute=0 rethrow=0 return_oop=0}
│ ; - java.util.ArrayList::elementData@5 (line 442)
│ ; - java.util.ArrayList::get@11 (line 459)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@20 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
1.71% │ 0x000000011153fb4c: mov 0x8(%r12,%r9,8),%r10d ; implicit exception: dispatches to 0x000000011153ff72
17.85% │ 0x000000011153fb51: cmp [=13=]x237522,%r10d ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Listener')}
0.00% │ 0x000000011153fb58: jne 0x000000011153fef6 ;*checkcast {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@25 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
3.79% │ 0x000000011153fb5e: mov %rdi,0x18(%rsp)
0.02% │ 0x000000011153fb63: mov %r8d,0x10(%rsp)
0.02% │ 0x000000011153fb68: mov %rbx,0x8(%rsp)
0.19% │ 0x000000011153fb6d: mov %r11,0x50(%rsp)
3.95% │ 0x000000011153fb72: mov %rdx,0x60(%rsp)
0.02% │ 0x000000011153fb77: mov %rcx,(%rsp)
0.03% │ 0x000000011153fb7b: mov %r13,0x58(%rsp)
0.36% │ 0x000000011153fb80: mov %rdx,%rsi
3.78% │ 0x000000011153fb83: mov [=13=]x1,%edx
0.01% │ 0x000000011153fb88: vzeroupper
4.05% │ 0x000000011153fb8b: callq 0x00000001114c2900 ; ImmutableOopMap{[80]=Oop [88]=Oop [96]=Oop [0]=Oop [16]=NarrowOop [24]=Oop }
│ ;*invokevirtual consume {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Listener::performAction@2 (line 53)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@29 (line 45)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
│ ; {optimized virtual_call}
0.98% │ 0x000000011153fb90: mov 0x10(%rsp),%r8d
3.61% │ 0x000000011153fb95: mov 0x10(%r12,%r8,8),%r10d ;*getfield singleListenerList {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@4 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.24% │ 0x000000011153fb9a: mov 0x8(%r12,%r10,8),%r9d ; implicit exception: dispatches to 0x000000011153ff9e
0.74% │ 0x000000011153fb9f: inc %ebp ;*iinc {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@32 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.04% │ 0x000000011153fba1: cmp [=13=]x237565,%r9d ; {metadata('com/nikoskatsanos/benchmarks/loops/SingleElementLoopBenchmark$Dispatcher')}
0.00% │ 0x000000011153fba8: jne 0x000000011153fd36
3.60% │ 0x000000011153fbae: lea (%r12,%r10,8),%r11 ;*invokeinterface size {reexecute=0 rethrow=0 return_oop=0}
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@7 (line 44)
│ ; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
│ ; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0.11% │ 0x000000011153fbb2: mov 0x10(%r11),%r9d
0.35% │ 0x000000011153fbb6: cmp %r9d,%ebp
╰ 0x000000011153fbb9: jge 0x000000011153fa9f ;*if_icmpge {reexecute=0 rethrow=0 return_oop=0}
; - com.benchmarks.loops.SingleElementLoopBenchmark$Dispatcher::invokeInLoop@12 (line 44)
; - com.benchmarks.loops.SingleElementLoopBenchmark::singleElementLoopInvocation@5 (line 28)
; - com.benchmarks.loops.generated.SingleElementLoopBenchmark_singleElementLoopInvocation_jmhTest::singleElementLoopInvocation_thrpt_jmhStub@17 (line 121)
0x000000011153fbbf: mov %ebp,%r9d
0x000000011153fbc2: mov 0x58(%rsp),%r13
0x000000011153fbc7: mov (%rsp),%rcx
0x000000011153fbcb: mov 0x60(%rsp),%rdx
0x000000011153fbd0: mov 0x50(%rsp),%r11
0x000000011153fbd5: mov 0x8(%rsp),%rbx
....................................................................................................
如果可能的话，我想要一些帮助来理解上面的两个输出。从我的理解来看，似乎在循环时，程序付出了相当大的代价来检查数组列表的大小以执行循环以及将对象转换为适当类型的成本，这是由于列表泛型.我无法真正理解循环是否展开，但我相信它会展开？
如果有人理解上面的输出并能给出一些指示来说明正在发生的事情，我们将不胜感激。
您衡量一个几乎什么都不做的操作与一个至少涉及四个相关内存加载的操作：
- ArrayList.size
- ArrayList.elementData
- elementData.length
- 元素数据[0]
再加上至少一次边界检查。我说 "at least"，因为这是最好的优化编译器可能做的事情。然而，HotSpot 执行两个绑定检查：一个在 ArrayList.get() 中，另一个用于 elementData 数组访问。
此外，ArrayList 包含一个对象数组，因此为了从列表中获取 Listener 的实例，需要将对象转换为目标类型。这是一个额外的内存负载加上类型检查。
从不同的角度看基准分数：单个元素列表不是慢 2.5 倍，而是长 3 纳秒：
Benchmark Mode Cnt Score Error Units
SingleElementLoopBenchmark.directInvocation avgt 5 2,340 ± 0,095 ns/op
SingleElementLoopBenchmark.singleElementLoopInvocation avgt 5 5,283 ± 0,074 ns/op
3 纳秒！ 这只是 2 GHz 内核的 6 CPU 个周期。光可以在 3 纳秒内传播不到 1 米。您真的期望 ArrayList 的开销比这少吗？不管开销多低，如果和完全没有开销相比，比例可以无限大。