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author | Kristjan Valur Jonsson <sweskman@gmail.com> | 2012-06-19 10:10:09 +0000 |
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committer | Kristjan Valur Jonsson <sweskman@gmail.com> | 2012-06-19 10:10:09 +0000 |
commit | e9485e555ea045b2c3e80b4a0c3647ec41768212 (patch) | |
tree | 878bf116395df611e03736feda4ff61f3b38375f /Python/condvar.h | |
parent | 1407541f5165fe64616a1bf779ede8dc51d6fc29 (diff) | |
download | cpython-e9485e555ea045b2c3e80b4a0c3647ec41768212.tar.gz |
Issue #15038:
Fix incorrect test of the condition variable state, spotted by
Richard Oudkerk. This could cause the internal condition variable
to grow without bounds.
Diffstat (limited to 'Python/condvar.h')
-rw-r--r-- | Python/condvar.h | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/Python/condvar.h b/Python/condvar.h index 8d3c595c40..29641654c5 100644 --- a/Python/condvar.h +++ b/Python/condvar.h @@ -177,7 +177,7 @@ PyMUTEX_UNLOCK(PyMUTEX_T *cs) typedef struct _PyCOND_T { HANDLE sem; - int waiting; + int waiting; /* to allow PyCOND_SIGNAL to be a no-op */ } PyCOND_T; Py_LOCAL_INLINE(int) @@ -222,6 +222,10 @@ _PyCOND_WAIT_MS(PyCOND_T *cv, PyMUTEX_T *cs, DWORD ms) * PyCOND_SIGNAL also decrements this value * and signals releases the mutex. This is benign because it * just means an extra spurious wakeup for a waiting thread. + * ('waiting' corresponds to the semaphore's "negative" count and + * we may end up with e.g. (waiting == -1 && sem.count == 1). When + * a new thread comes along, it will pass right throuhgh, having + * adjusted it to (waiting == 0 && sem.count == 0). */ if (wait == WAIT_FAILED) @@ -246,10 +250,14 @@ PyCOND_TIMEDWAIT(PyCOND_T *cv, PyMUTEX_T *cs, long us) Py_LOCAL_INLINE(int) PyCOND_SIGNAL(PyCOND_T *cv) { - if (cv->waiting) { + /* this test allows PyCOND_SIGNAL to be a no-op unless required + * to wake someone up, thus preventing an unbounded increase of + * the semaphore's internal counter. + */ + if (cv->waiting > 0) { /* notifying thread decreases the cv->waiting count so that - * a delay between notify and wakeup doesn't cause a number - * of extra ReleaseSemaphore calls + * a delay between notify and actual wakeup of the target thread + * doesn't cause a number of extra ReleaseSemaphore calls. */ cv->waiting--; return ReleaseSemaphore(cv->sem, 1, NULL) ? 0 : -1; @@ -260,7 +268,7 @@ PyCOND_SIGNAL(PyCOND_T *cv) Py_LOCAL_INLINE(int) PyCOND_BROADCAST(PyCOND_T *cv) { - if (cv->waiting) { + if (cv->waiting > 0) { return ReleaseSemaphore(cv->sem, cv->waiting, NULL) ? 0 : -1; cv->waiting = 0; } |