Name: wm7046 Date: 08/01/97


The Problem

Here is what I did:


D:\javabugs\sample>jdb "-Dhotjava.home=D:\Hotjava" "-Dapplet.allow.namespace=true" sun.hotjava.Main
file:D:\javabugs\sample\sample.html
Initializing jdb...
0xf73128:class(sun.hotjava.Main)
> stop in sample.init
Breakpoint set in sample.init
> run
run sun.hotjava.Main file:D:\javabugs\sample\sample.html
running ...
main[1] [Starting HotJava]
[Initializing globals]
[Creating frame]
[Loading: C:\\.hotjava\urlpool]
[Loaded DTD html32 in 687ms]

Breakpoint hit: sample.init (sample:107)
thread applet-sample.class[1] list
103 // CreateControls() method from within this method. Remove the following
104 // call to resize() before adding the call to CreateControls();
105 // CreateControls() does its own resizing.
106 //----------------------------------------------------------------------
107 => resize(320, 240);
108
109 // TODO: Place additional initialization code here
110 }
111
thread applet-sample.class[1] next
thread applet-sample.class[1]
Breakpoint hit: sample.init (sample:99)
thread applet-sample.class[1] stop in sample.displayImage



At this point it was locked up. Totally.

This problem was discovered with a Sparkler (1.1.4) prerelease. The problem occurs fairly infrequently - I've seen it 3 times out of maybe 20 to 30 attempts. It may be difficult to reproduce.

Our Analysis

The hang occurred because a program thread had been suspended holding a monitor on a Class object (the Class object for java.text.BreakIterator). After this thread was suspended, as part of new breakpoint processing, the debugger Agent called java.lang.Class.getInterfaces for the class in which the breakpoint was to be set. This caused class loading to take place for this class, and eventually caused the Agent thread to require the monitor for the same Class object (java.text.BreakIterator). The result is a deadlock. It is not at all clear how a deadlock such as this is to be avoided.

The calling traces for the two threads may be helpful here. They are (Agent thread)


NtWaitForSingleObject@12 + 11 bytes
RtlpWaitForCriticalSection@4 + 170 bytes
RtlEnterCriticalSection@4 + 67 bytes
sysMonitorEnter(sys_mon * 0x008512e8) line 91
monitorEnter(unsigned int 16330096) line 47 + 12 bytes
ResolveClass(Hjava_lang_Class * 0x00f92d70, char * * 0x0201f5e8) line 546 + 9 bytes
java_lang_Class_getInterfaces(Hjava_lang_Class * 0x00f92d70) line 123 + 13 bytes
Java_java_lang_Class_getInterfaces_stub(stack_item * 0x01d4b0e0, execenv * 0x0201ff10) line 107 + 11 bytes
invokeNativeMethod(Hjava_lang_Object * 0x00f92d70, methodblock * 0x01cf5020, int 1, execenv * 0x0201ff10) line 224 + 14 bytes
ExecuteJava(unsigned char * 0x0201fe60, execenv * 0x0201ff10) line 1447 + 22 bytes
do_execute_java_method_vararg(execenv * 0x0201ff10, void * 0x00f65620, char * 0x1007df2c, char * 0x1007df28, methodblock * 0x00000000, int 0, char * 0x0201fefc, long * 0x00000000, int 0) line 601 + 13 bytes
execute_java_dynamic_method(execenv * 0x0201ff10, Hjava_lang_Object * 0x00f65620, char * 0x1007df2c, char * 0x1007df28) line 283 + 33 bytes
ThreadRT0(Hjava_lang_Thread * 0x00f65620) line 61 + 23 bytes
_start(sys_thread * 0x0087c880) line 244 + 13 bytes
MSVCRT! 779f585d()



and (user thread)


NtWaitForSingleObject@12 + 11 bytes
RtlpWaitForCriticalSection@4 + 170 bytes
RtlEnterCriticalSection@4 + 67 bytes
sysMonitorEnter(sys_mon * 0x00860e60) line 91
FindClassFromClass(execenv * 0x02c8ff10, char * 0x028d8f58, int 0, Hjava_lang_Class * 0x00f92d70) line 967 + 11 bytes
Locked_InitializeClass(Hjava_lang_Class * 0x00f92d70, char * * 0x02c8f354) line 691 + 24 bytes
InitializeClass(Hjava_lang_Class * 0x00f92d70, char * * 0x02c8f354) line 536 + 13 bytes
InitializeAndResolveClass(Hjava_lang_Class * 0x00f92d70, int 1) line 889 + 13 bytes
FindClassFromClass(execenv * 0x02c8ff10, char * 0x028ecea0, int 1, Hjava_lang_Class * 0x00f80108) line 978 + 13 bytes
Locked_ResolveClassConstant(Hjava_lang_Class * 0x00f80108, cp_item_type * 0x028eb988, unsigned int 19, execenv * 0x02c8ff10, unsigned int 128) line 218 + 19 bytes
Locked_ResolveClassConstantField(unsigned int 10, Hjava_lang_Class * 0x00f80108, cp_item_type * 0x028eb988, unsigned int 74, execenv * 0x02c8ff10) line 337 + 29 bytes
Locked_ResolveClassConstant(Hjava_lang_Class * 0x00f80108, cp_item_type * 0x028eb988, unsigned int 74, execenv * 0x02c8ff10, unsigned int 1024) line 311 + 25 bytes
ResolveClassConstant(cp_item_type * 0x028eb988, unsigned int 74, execenv * 0x02c8ff10, unsigned int 1024) line 181 + 25 bytes
ResolveClassConstantFromPC(unsigned char * 0x028ee5a0, unsigned char 184, cp_item_type * 0x028eb988, execenv * 0x02c8ff10, unsigned int 1024) line 1272 + 21 bytes
ExecuteJava(unsigned char * 0x02c8fe60, execenv * 0x02c8ff10) line 1058 + 70 bytes
do_execute_java_method_vararg(execenv * 0x02c8ff10, void * 0x00f84cd8, char * 0x1007df2c, char * 0x1007df28, methodblock * 0x00000000, int 0, char * 0x02c8fefc, long * 0x00000000, int 0) line 601 + 13 bytes
execute_java_dynamic_method(execenv * 0x02c8ff10, Hjava_lang_Object * 0x00f84cd8, char * 0x1007df2c, char * 0x1007df28) line 283 + 33 bytes
ThreadRT0(Hjava_lang_Thread * 0x00f84cd8) line 61 + 23 bytes
_start(sys_thread * 0x008a5f80) line 244 + 13 bytes
MSVCRT! 779f585d()
BaseThreadStart@8 + 81 bytes
======================================================================
john.bui@eng 1997-10-17

No specific test case available. Implicity tested, closed with exposure.