一个for循环带来的逃逸问题整懵了

一个对象与使用之间，插入一段循环，逃逸就会失败，算是记住一个知识点吧

java8 14 都尝试过，逃逸分析的逻辑应该一样

class Ctx {
    private String name;

     public Ctx(String name) {
         this.name = name;
     }

     public String getName() {
         return name;
     }

     public void doNothing() {

     }
 }

public class Test {
    public static void main(String[] args) {
        for (long i = 0; i < Long.MAX_VALUE; ++i) {
            Ctx ctx = new Ctx("name");
            // 逃逸成功
            ctx.doNothing();
            for (int c = 0; c < 4; c++) {

            }
            // 会逃逸失败
            // ctx.doNothing();
        }
    }
}

逃逸失败的记录

java -Xmx30M -XX:+PrintEscapeAnalysis -XX:+PrintEliminateAllocations -XX:+PrintInlining -XX:+Verbose Test

@ 1 java.lang.CharacterData::of (120 bytes) @ 17 java.lang.AbstractStringBuilder::newCapacity (39 bytes) callee is too large
@ 4 @ 20 java.util.Arrays::copyOf (19 bytes)
@ 11 java.lang.Math::min (11 bytes)
callee is too large
@ 5 java.lang.CharacterData::toLowerCase (0 bytes) no static binding
@ 66 java.lang.String::indexOfSupplementary java.lang.CharacterDataLatin1::getProperties (71 bytes) callee is too large
@ 14 java.lang.System::arraycopy (0 bytes) intrinsic
(11 bytes)
@ 7 java.lang.AbstractStringBuilder::ensureCapacityInternal (27 bytes)
@ 7 java.lang.AbstractStringBuilder::append (29 bytes)
@ 7 java.lang.AbstractStringBuilder::ensureCapacityInternal (27 bytes)
@ 9 java/lang/StringIndexOutOfBoundsException @ 17 java.lang.AbstractStringBuilder::newCapacity @ 17 java.lang.AbstractStringBuilder::newCapacity (39 bytes) callee is too large
(39 bytes) callee is too large
::<init> (not loaded) not inlineable
@ 20 java.util.Arrays::copyOf (19 bytes)
@ 20 java.util.Arrays::copyOf @ 27 java/lang/StringIndexOutOfBoundsException::<init> (not loaded) not inlineable
(19 bytes)
@ 11 java.lang.Math::min @ 43 java/lang/StringIndexOutOfBoundsException::<init> (not loaded) not inlineable
(11 bytes)
@ 11 java.lang.Math::min @ 58 java.lang.System::arraycopy (11 bytes)
@ 14 java.lang.System::arraycopy (0 bytes) intrinsic
(0 bytes) intrinsic
@ 14 java.lang.System::arraycopy (0 bytes) intrinsic
@ 1 java.lang.Object::<init> (1 bytes)
@ 1 java.lang.Object::<init> (1 bytes) inline (hot)
@ 16 Ctx::<init> (10 bytes)
@ 1 java.lang.Object::<init> (1 bytes)
@ 36 Ctx::doNothing (1 bytes)
@ 16 Ctx::<init> (10 bytes)
@ 1 java.lang.Object::<init> (1 bytes)
@ 36 Ctx::doNothing (1 bytes)
EA: 2 iterations to build connection graph with 276 nodes and worklist size 21

======== Connection graph for Test::main
JavaObject NoEscape(NoEscape) NSR [ 235F [ 184 189 272 ]] 172 Allocate === 161 268 132 8 1 ( 28 45 20 1 1 152 1 1 1 ) [[ 173 174 175 182 183 184 ]] rawptr:NotNull ( int:>=0, java/lang/Object:NotNull *, bool, top ) Test::main @ bci:10 Type:{0:control, 1:abIO, 2:memory, 3:rawptr:BotPTR, 4:return_address, 5:rawptr:NotNull} !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 172P [ 189 235b ]] 184 Proj === 172 [[ 185 189 235 ]] #5 Type:rawptr:NotNull !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 184 172P [ 272 ]] 189 CheckCastPP === 186 184 [[ 238 272 ]] Oop:Ctx:NotNull:exact * !orig=[265],[111],[126] !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 47 189 1P 48P 172P [ ]] 272 Phi === 267 47 189 [[ 133 124 ]] Oop:Ctx:BotPTR * !orig=[111],[126] !jvms: Test::main @ bci:23

=== No allocations eliminated for Test::main since there are no scalar replaceable candidates ===
@ 36 Ctx::doNothing (1 bytes) inline (hot)
@ 16 Ctx::<init> (10 bytes) inline (hot)
@ 1 java.lang.Object::<init> (1 bytes) inline (hot)

成功逃逸的记录

java -Xmx30M -XX:+PrintEscapeAnalysis -XX:+PrintEliminateAllocations -XX:+PrintInlining -XX:+Verbose Test

======== Connection graph for Test::main
JavaObject NoEscape(NoEscape) [ 160F [ 108 113 ]] 96 Allocate === 84 72 76 8 1 ( 28 94 20 1 1 75 1 1 1 ) [[ 97 98 99 106 107 108 ]] rawptr:NotNull ( int:>=0, java/lang/Object:NotNull *, bool, top ) Test::main @ bci:10 Type:{0:control, 1:abIO, 2:memory, 3:rawptr:BotPTR, 4:return_address, 5:rawptr:NotNull} !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 96P [ 113 160b ]] 108 Proj === 96 [[ 109 113 160 ]] #5 Type:rawptr:NotNull !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 108 96P [ ]] 113 CheckCastPP === 110 108 [[ 163 ]] Oop:Ctx:NotNull:exact * !jvms: Test::main @ bci:10

Scalar 113 CheckCastPP === 110 108 [[ 163 ]] Oop:Ctx:NotNull:exact *,iid=96 !jvms: Test::main @ bci:10
++++ Eliminated: 96 Allocate
@ 16 Ctx::<init> (10 bytes) inline (hot)
@ 1 java.lang.Object::<init> (1 bytes) inline (hot)
@ 21 Ctx::doNothing (1 bytes) inline (hot)
EA: 2 iterations to build connection graph with 227 nodes and worklist size 13

======== Connection graph for Test::main
JavaObject NoEscape(NoEscape) [ 181F [ 129 134 ]] 117 Allocate === 105 219 90 8 1 ( 28 115 20 1 1 96 1 1 1 ) [[ 118 119 120 127 128 129 ]] rawptr:NotNull ( int:>=0, java/lang/Object:NotNull *, bool, top ) Test::main @ bci:10 Type:{0:control, 1:abIO, 2:memory, 3:rawptr:BotPTR, 4:return_address, 5:rawptr:NotNull} !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 117P [ 134 181b ]] 129 Proj === 117 [[ 130 134 181 ]] #5 Type:rawptr:NotNull !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 129 117P [ ]] 134 CheckCastPP === 131 129 [[ 184 ]] Oop:Ctx:NotNull:exact * !jvms: Test::main @ bci:10

Scalar 134 CheckCastPP === 131 129 [[ 184 ]] Oop:Ctx:NotNull:exact *,iid=117 !jvms: Test::main @ bci:10
++++ Eliminated: 117 Allocate
@ 16 Ctx::<init> (10 bytes) inline (hot)
@ 1 java.lang.Object::<init> (1 bytes) inline (hot)
@ 21 Ctx::doNothing (1 bytes) inline (hot)
EA: 2 iterations to build connection graph with 254 nodes and worklist size 12

======== Connection graph for Test::main
JavaObject NoEscape(NoEscape) [ 137F [ 85 90 ]] 73 Allocate === 244 65 241 8 1 ( 71 70 25 1 1 67 1 1 1 ) [[ 74 75 76 83 84 85 ]] rawptr:NotNull ( int:>=0, java/lang/Object:NotNull *, bool, top ) Test::main @ bci:10 Type:{0:control, 1:abIO, 2:memory, 3:rawptr:BotPTR, 4:return_address, 5:rawptr:NotNull} !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 73P [ 90 137b ]] 85 Proj === 73 [[ 86 90 137 ]] #5 Type:rawptr:NotNull !jvms: Test::main @ bci:10
LocalVar NoEscape(NoEscape) [ 85 73P [ ]] 90 CheckCastPP === 87 85 [[ 140 ]] Oop:Ctx:NotNull:exact * !jvms: Test::main @ bci:10

Scalar 90 CheckCastPP === 87 85 [[ 140 ]] Oop:Ctx:NotNull:exact *,iid=73 !jvms: Test::main @ bci:10
++++ Eliminated: 73 Allocate
@ 16 Ctx::<init> (10 bytes) inline (hot)
@ 1 java.lang.Object::<init> (1 bytes) inline (hot)
@ 21 Ctx::doNothing (1 bytes) inline (hot)

一个for循环带来的逃逸问题整懵了

本月精选性能专题

本月精选线上案例

本月精选原创好文

联系我们

网媒渠道

友情链接