Update of /projects/cvsroot/python/dist/src/Python
In directory eric:/projects/python/develop/guido/src/Python
Modified Files:
thread_nt.h
Log Message:
Bill Tutt:
Calling Sleep(0) for a spinlock can cause a priority inversion, adding
comments to explain what's going on.
Index: thread_nt.h
===================================================================
RCS file: /projects/cvsroot/python/dist/src/Python/thread_nt.h,v
retrieving revision 2.8
retrieving revision 2.9
diff -C2 -r2.8 -r2.9
*** thread_nt.h 2000/05/05 14:29:59 2.8
--- thread_nt.h 2000/05/11 12:53:51 2.9
***************
*** 51,57 ****
static LONG spinlock = 0 ;
PVOID result ;
/* Acqire spinlock (yielding control to other threads if cant aquire for the moment) */
! while(InterlockedExchange(&spinlock, 1)) Sleep(0) ;
result = *dest ;
if (result == comperand)
--- 51,80 ----
static LONG spinlock = 0 ;
PVOID result ;
+ DWORD dwSleep = 0;
/* Acqire spinlock (yielding control to other threads if cant aquire for the moment) */
! while(InterlockedExchange(&spinlock, 1))
! {
! // Using Sleep(0) can cause a priority inversion.
! // Sleep(0) only yields the processor if there's
! // another thread of the same priority that's
! // ready to run. If a high-priority thread is
! // trying to acquire the lock, which is held by
! // a low-priority thread, then the low-priority
! // thread may never get scheduled and hence never
! // free the lock. NT attempts to avoid priority
! // inversions by temporarily boosting the priority
! // of low-priority runnable threads, but the problem
! // can still occur if there's a medium-priority
! // thread that's always runnable. If Sleep(1) is used,
! // then the thread unconditionally yields the CPU. We
! // only do this for the second and subsequent even
! // iterations, since a millisecond is a long time to wait
! // if the thread can be scheduled in again sooner
! // (~100,000 instructions).
! // Avoid priority inversion: 0, 1, 0, 1,...
! Sleep(dwSleep);
! dwSleep = !dwSleep;
! }
result = *dest ;
if (result == comperand)
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