EVALUATION
See main CR
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EVALUATION
http://hg.openjdk.java.net/hsx/hotspot-comp/hotspot/rev/16f9fa2bf76c
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SUGGESTED FIX
http://www.sapjvm.com/as/webrevs/atomic_array_copy/hg_hsx_hotspotmain.patch
--- old/src/os_cpu/windows_x86/vm/copy_windows_x86.inline.hpp 2011-10-13 12:08:44.918387900 +0200
+++ new/src/os_cpu/windows_x86/vm/copy_windows_x86.inline.hpp 2011-10-13 12:08:44.236319700 +0200
@@ -85,13 +85,13 @@
}
static void pd_conjoint_jshorts_atomic(jshort* from, jshort* to, size_t count) {
- // FIXME
- (void)memmove(to, from, count << LogBytesPerShort);
+ // SAPJVM AS 2011-09-30. memmove might copy byte-wise.
+ copy_conjoint_atomic<jshort>( from, to, count);
}
static void pd_conjoint_jints_atomic(jint* from, jint* to, size_t count) {
- // FIXME
- (void)memmove(to, from, count << LogBytesPerInt);
+ // SAPJVM AS 2011-09-30. memmove might copy byte-wise.
+ copy_conjoint_atomic<jint>( from, to, count);
}
static void pd_conjoint_jlongs_atomic(jlong* from, jlong* to, size_t count) {
@@ -128,20 +128,7 @@
}
static void pd_conjoint_oops_atomic(oop* from, oop* to, size_t count) {
- // Do better than this: inline memmove body NEEDS CLEANUP
- if (from > to) {
- while (count-- > 0) {
- // Copy forwards
- *to++ = *from++;
- }
- } else {
- from += count - 1;
- to += count - 1;
- while (count-- > 0) {
- // Copy backwards
- *to-- = *from--;
- }
- }
+ copy_conjoint_atomic<oop>( from, to, count);
}
static void pd_arrayof_conjoint_bytes(HeapWord* from, HeapWord* to, size_t count) {
--- old/src/share/vm/utilities/copy.hpp 2011-10-13 12:08:52.253121300 +0200
+++ new/src/share/vm/utilities/copy.hpp 2011-10-13 12:08:51.779073900 +0200
@@ -54,6 +54,25 @@
}
class Copy : AllStatic {
+
+ // SAPJVM AS 2011-09-20. Template for atomic copy.
+ template <class T> static void copy_conjoint_atomic(T* from, T* to, size_t count)
+ {
+ if (from > to) {
+ while (count-- > 0) {
+ // Copy forwards
+ *to++ = *from++;
+ }
+ } else {
+ from += count - 1;
+ to += count - 1;
+ while (count-- > 0) {
+ // Copy backwards
+ *to-- = *from--;
+ }
+ }
+ }
+
public:
// Block copy methods have four attributes. We don't define all possibilities.
// alignment: aligned to BytesPerLong
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EVALUATION
Compressed oops utilizes pd_conjoint_jints_atomic which should atomically copy jints from the src to dest locations. But on win32 we have the following in copy_windows_x96.inline.hpp:
static void pd_conjoint_jshorts_atomic(jshort* from, jshort* to, size_t count) {
// FIXME
(void)memmove(to, from, count << LogBytesPerShort);
}
static void pd_conjoint_jints_atomic(jint* from, jint* to, size_t count) {
// FIXME
(void)memmove(to, from, count << LogBytesPerInt);
}
It is unclear whether the FIXME refers to the atomicity issue or relates to earlier performance work (5039509) but memmove is well known to not be guaranteed to be atomic (its use was replaced on solaris for example). According to the submitter on win32 it will copy byte-by-byte until it reaches an 8-byte aligned address and then copy 64-bits at a time (presumably only on 64-bit systems).
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PUBLIC COMMENTS
I slightly modified the test program to print the incorrect class name:
public class TestConjointAtomicArraycopy {
static volatile Object [] testArray = new Object [4];
public static void main(String[] args ) throws InterruptedException{
for (int i = 0; i < testArray.length; i++){
testArray[i] = new String("A");
}
Thread writer = new Thread (new Runnable(){
public void run(){
for (int i = 0 ; i < 1000000; i++) {
System.arraycopy(testArray, 1, testArray, 0, 3);
testArray[2] = new String("a");
}
}
});
Thread reader = new Thread( new Runnable(){
public void run(){
while ( true){
String name = testArray[2].getClass().getName();
if(!(name.endsWith("String"))){
throw new RuntimeException("got wrong class name:" + name);
}
}
}
});
reader.start();
writer.start();
writer.join();
System.out.println("Test passed.");
System.exit(0);
}
}
and on 64-bit windows it crashed the VM!
#
# A fatal error has been detected by the Java Runtime Environment:
#
# EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x000000006d72057a, pid=5660, tid=5020
#
# JRE version: 8.0-b02
# Java VM: Java HotSpot(TM) 64-Bit Server VM (22.0-b01 mixed mode windows-amd64 compressed oops)
# Problematic frame:
# V [jvm.dll+0xf057a]
#
# Failed to write core dump. Minidumps are not enabled by default on client versions of Windows
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#
--------------- T H R E A D ---------------
Current thread (0x00000000066a5000): JavaThread "Thread-1" [_thread_in_vm, id=5020, stack(0x0000000007bb0000,0x0000000007cb0000)]
siginfo: ExceptionCode=0xc0000005, reading address 0x0000000000000078
Registers:
RAX=0x0000000000000000, RBX=0x00000000066a5000, RCX=0x0000000000000003, RDX=0x0000000000000000
RSP=0x0000000007caf740, RBP=0x0000000007caf7f8, RSI=0x00000000066a51d0, RDI=0x0000000007caf818
R8 =0x0000000000000004, R9 =0x00000007d5ef9450, R10=0x00000000028021bc, R11=0x000000006d7e96b0
R12=0x0000000000000000, R13=0x000000077ca022f8, R14=0x0000000007caf818, R15=0x00000000066a5000
RIP=0x000000006d72057a, EFLAGS=0x0000000000010246
Top of Stack: (sp=0x0000000007caf740)
0x0000000007caf740: 0000000007caf7b8 000000077caade48
0x0000000007caf750: 0000000000000000 000000077ca07d38
0x0000000007caf760: 00000000066a5000 0000000000000000
0x0000000007caf770: 0000000007caf800 00000000027f6330
0x0000000007caf780: 00000000027f6213 00000000028021e9
0x0000000007caf790: 000000077ca022f8 0000000007caf7f8
0x0000000007caf7a0: 00000000066a5000 000000000000000a
0x0000000007caf7b0: 00000007d5f51c68 0000000007caf7b8
0x0000000007caf7c0: 0000000000000000 0000000007caf818
0x0000000007caf7d0: 000000077caa9a88 0000000000000000
0x0000000007caf7e0: 000000077ca022f8 0000000000000000
0x0000000007caf7f0: 0000000007caf818 0000000007caf860
0x0000000007caf800: 00000000027f6213 0000000000000000
0x0000000007caf810: 00000000027ff01b 00000007d5ffa0c8
0x0000000007caf820: 0000000007caf820 000000077cc4cd55
0x0000000007caf830: 0000000007caf878 000000077cc4d0a0
Instructions: (pc=0x000000006d72057a)
0x000000006d72055a: 00 00 48 8b 17 74 15 8b 52 08 8b 0d be 8b 52 00
0x000000006d72056a: 48 d3 e2 48 03 15 ac 8b 52 00 eb 04 48 8b 52 08
0x000000006d72057a: 48 8b 52 78 48 8b ce e8 6a 4b 0b 00 48 83 7c 24
0x000000006d72058a: 28 00 48 8b f0 74 0a 48 8d 4c 24 20 e8 65 1d 10
Register to memory mapping:
RAX=0x0000000000000000 is an unknown value
RBX=0x00000000066a5000 is a thread
RCX=0x0000000000000003 is an unknown value
RDX=0x0000000000000000 is an unknown value
RSP=0x0000000007caf740 is pointing into the stack for thread: 0x00000000066a5000
RBP=0x0000000007caf7f8 is pointing into the stack for thread: 0x00000000066a5000
RSI=0x00000000066a51d0 is an unknown value
RDI=0x0000000007caf818 is pointing into the stack for thread: 0x00000000066a5000
R8 =0x0000000000000004 is an unknown value
R9 =0x00000007d5ef9450 is an oop
java.lang.Class
- klass: 'java/lang/Class'
R10=0x00000000028021bc is an Interpreter codelet
method entry point (kind = native) [0x0000000002801f40, 0x00000000028027c0] 2176 bytes
R11=0x000000006d7e96b0 is an unknown value
R12=0x0000000000000000 is an unknown value
R13=0x000000077ca022f8 is an oop
{method}
- klass: {other class}
R14=0x0000000007caf818 is pointing into the stack for thread: 0x00000000066a5000
R15=0x00000000066a5000 is a thread
Stack: [0x0000000007bb0000,0x0000000007cb0000], sp=0x0000000007caf740, free space=1021k
Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
V [jvm.dll+0xf057a]
j TestConjointAtomicArraycopy$2.run()V+5
j java.lang.Thread.run()V+11
v ~StubRoutines::call_stub
V [jvm.dll+0x1a3926]
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j java.lang.Object.getClass()Ljava/lang/Class;+0
j TestConjointAtomicArraycopy$2.run()V+5
j java.lang.Thread.run()V+11
v ~StubRoutines::call_stub
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PUBLIC COMMENTS
Crash does not happen with -XX:-UseCompressedOops
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Java