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Date: Fri, 18 May 2007 07:36:16 -0700 (PDT)
From: "Ilya Leviev (JIRA)" <jira@apache.org>
To: commits@harmony.apache.org
Subject: [jira] Created: (HARMONY-3912) [drlvm][thread] Race conditions at
 "thread_native_thin_monitor.c":78 and "thread_java_monitors.c":361/362
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[drlvm][thread] Race conditions at "thread_native_thin_monitor.c":78 and "thread_java_monitors.c":361/362
---------------------------------------------------------------------------------------------------------

                 Key: HARMONY-3912
                 URL: https://issues.apache.org/jira/browse/HARMONY-3912
             Project: Harmony
          Issue Type: Bug
          Components: DRLVM
         Environment: win2003
            Reporter: Ilya Leviev


TC report on thread unsafe access that result in 2 race conditions that occur during concurrent execution of set_fat_lock_id and hythread_thin_monitor_enter functions.


Write -> Read data-race	
Memory read at "thread_native_thin_monitor.c":361 conflicts with a prior memory write at "thread_native_thin_monitor.c":78


Write -> Read data-race	
Memory read at "thread_native_thin_monitor.c":362 conflicts with a prior memory write at "thread_native_thin_monitor.c":78


Stack Trace: 


Context
	Function void JIT_execute_method_default(void *,struct _jmethodID *,union jvalue *,union jvalue *) "ini_ia32.cpp":199
	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":341
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function jthread_monitor_enter "thread_java_monitors.c":123
	Function hythread_thin_monitor_enter "thread_native_thin_monitor.c":349

1st Access
	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":341
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function jthread_monitor_enter "thread_java_monitors.c":135
	Function inflate_lock "thread_native_thin_monitor.c":600
	Function set_fat_lock_id "thread_native_thin_monitor.c":78


"76"	""	"     lockword&=0x7FF;"
"77"	""	"     lockword|=(monitor_id << 11) | 0x80000000;"
"78"	"*"	"     *lockword_ptr=lockword;"
"79"	""	"     apr_memory_rw_barrier();"


2nd Access
	Function void JIT_execute_method_default(void *,struct _jmethodID *,union jvalue *,union jvalue *) "ini_ia32.cpp":199
	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":341
	Function class VM_thread * get_thread_ptr_stub(void) "thread_manager.cpp":138
	Function jthread_monitor_enter "thread_java_monitors.c":123
	Function hythread_thin_monitor_enter "thread_native_thin_monitor.c":361/362


"360"	""	"     while (hythread_thin_monitor_try_enter(lockword_ptr) == TM_ERROR_EBUSY) {"
"361"	"*"	"         if (IS_FAT_LOCK(*lockword_ptr)) {"
"362"	"*"	"             fat_monitor = locktable_get_fat_monitor(FAT_LOCK_ID(*lockword_ptr)); //  find fat_monitor in lock table"
"363"	""	"             TRACE(("" lock %d\n"", FAT_LOCK_ID(*lockword_ptr)));"
"364"	""	"             saved_disable_count=reset_suspend_disable();"


See also Source View screenshot.


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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