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From "Ilya Leviev (JIRA)" <j...@apache.org>
Subject [jira] Created: (HARMONY-3920) [drlvm][thread] Race conditions at "apr_atomic.c":102" and thread_native_thin_monitor.c:502
Date Mon, 21 May 2007 11:34:18 GMT
[drlvm][thread] Race conditions at "apr_atomic.c":102" and thread_native_thin_monitor.c:502
-------------------------------------------------------------------------------------------

                 Key: HARMONY-3920
                 URL: https://issues.apache.org/jira/browse/HARMONY-3920
             Project: Harmony
          Issue Type: Bug
          Components: DRLVM
            Reporter: Ilya Leviev



TC report on thread unsafe access that result in race condition that occur during concurrent
execution of apr_atomic_cas32 and hythread_thin_monitor_notify functions.

Write -> Read data-race	
Memory read at "thread_native_thin_monitor.c":502 conflicts with a prior memory write at "apr_atomic.c":102


Stack Trace: 


Context
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function m2n_free_local_handles "m2n_ia32.cpp":268
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function m2n_free_local_handles "m2n_ia32.cpp":268
	Function hythread_thin_monitor_try_enter "thread_native_thin_monitor.c":341
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function hythread_suspend_enable "hythread_ext.h":370
	Function Java_java_lang_VMThreadManager_notify "java_lang_vmthreadmanager.cpp":96
	Function jthread_monitor_notify "thread_java_monitors.c":222
	Function hythread_thin_monitor_notify "thread_native_thin_monitor.c":500


1st Access
	Function void DrlEMImpl::executeMethod(struct _jmethodID *,union jvalue *,union jvalue *)
"drlemimpl.cpp":509
	Function void JIT_execute_method_default(void *,struct _jmethodID *,union jvalue *,union
jvalue *) "ini_ia32.cpp":223
	Function vm_invoke_native_array_stub "ini_ia32.cpp":76
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function m2n_free_local_handles "m2n_ia32.cpp":268
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function m2n_free_local_handles "m2n_ia32.cpp":268
	Function hythread_thin_monitor_try_enter "thread_native_thin_monitor.c":323
	Function unreserve_lock "thread_native_thin_monitor.c":180:

	"179"	""	"         if (lockword == apr_atomic_cas32 (((volatile apr_uint32_t*) lockword_ptr),
"
	"180"	""	"                 (apr_uint32_t) lockword_new, lockword)) {"
	"181"	""	"             TRACE((""unreserved lock""));"


	Function apr_atomic_cas32 "apr_atomic.c":102:

	"96"	""	" APR_DECLARE(apr_uint32_t) apr_atomic_cas32(volatile apr_uint32_t *mem, apr_uint32_t
with,"
	"97"	""	"                                            apr_uint32_t cmp)"
	"98"	""	" {"
	"99"	""	" #if (defined(_M_IA64) || defined(_M_AMD64)) && !defined(RC_INVOKED)"
	"100"	""	"     return InterlockedCompareExchange(mem, with, cmp);"
	"101"	""	" #else"
	"102"	"*"	"     return ((apr_atomic_win32_ptr_val_val_fn)InterlockedCompareExchange)(mem,
with, cmp);"
	"103"	""	" #endif"
	"104"	""	" }"




2nd Access
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function m2n_free_local_handles "m2n_ia32.cpp":268
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function m2n_free_local_handles "m2n_ia32.cpp":268
	Function hythread_thin_monitor_try_enter "thread_native_thin_monitor.c":341
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function hythread_suspend_enable "hythread_ext.h":370
	Function Java_java_lang_VMThreadManager_notify "java_lang_vmthreadmanager.cpp":96
	Function jthread_monitor_notify "thread_java_monitors.c":222
	Function hythread_thin_monitor_notify "thread_native_thin_monitor.c":502


"500"	""	" IDATA hythread_thin_monitor_notify(hythread_thin_monitor_t *lockword_ptr) {"
"501"	""	"     hythread_monitor_t fat_monitor;"
"502"	"*"	"     hythread_thin_monitor_t lockword = *lockword_ptr;"
"503"	""	"     if (IS_FAT_LOCK(lockword)) {"
"504"	""	"          fat_monitor = locktable_get_fat_monitor(FAT_LOCK_ID(lockword));"



See also Source View screenshots.



Notes on Write->Read race condition.
------------------------------------
Write->Read data races occur when one thread writes a shared memory location (address)
while another thread concurrently reads the same memory location.  
The shared memory location may be referred to by (variable) name, pointer, or even a function
such as memcpy().  

The following example uses a variable name:

1st access by first thread

S1: sharedX = privateA

2nd access by second thread

S2: privateB = sharedX

If sharedX is a variable visible to all threads and privateA and privateB are local variables
visible only to the thread where each was declared,
 concurrent execution of the above statements by multiple threads results in a "race" on the
value to be read from sharedX.   

Since the order of execution among threads is unpredictable, it is unknown which value will
be available in sharedX to be stored into privateB.  
This results in non-deterministic software, or software prone to produce different results
each time it is executed. 
_______________________________________________________________________________________________________________________






If it not affect correctness of execution I will mark it by special API for prevention of
further alarms on this race.




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