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Cleanups for mutex utilities #3912

Merged
merged 12 commits into from
Aug 11, 2023
Merged

Cleanups for mutex utilities #3912

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bb5dec0
cache the result of `GetCurrentThreadId`
achabense Jul 30, 2023
31adc56
logic cleanups
achabense Jul 30, 2023
a11a3d1
hide `_Mtx_timedlock` and `_Mtx_getconcrtcs`
achabense Jul 30, 2023
7c03c3d
Enhancement: Guard 6 declarations with `#ifdef _CRTBLD`, comment why.
StephanTLavavej Aug 2, 2023
0b7a6e6
Fix bincompat: Copy `_CRTIMP2_PURE` and `__cdecl` from `xthreads.h`.
StephanTLavavej Aug 2, 2023
19a88ac
Style: Use `auto` after `static_cast`.
StephanTLavavej Aug 2, 2023
a3783df
Style: After `if`-`return`, avoid `else`.
StephanTLavavej Aug 2, 2023
9b55a45
Comment that `_Mtx_plain` is for `_Thrd_create`.
StephanTLavavej Aug 2, 2023
19c1dee
Merge branch 'microsoft:main' into _Mtx_cleanups
achabense Aug 9, 2023
9fb5e72
remove redundant assignments
achabense Aug 9, 2023
61353c9
Drop "// used only by MEOW" comments.
StephanTLavavej Aug 10, 2023
1dfc68e
Merge branch 'main' into _Mtx_cleanups
StephanTLavavej Aug 11, 2023
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2 changes: 0 additions & 2 deletions stl/inc/xthreads.h
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Original file line number Diff line number Diff line change
Expand Up @@ -111,10 +111,8 @@ _CRTIMP2_PURE void __cdecl _Mtx_destroy_in_situ(_Mtx_t);
_CRTIMP2_PURE int __cdecl _Mtx_current_owns(_Mtx_t);
_CRTIMP2_PURE _Thrd_result __cdecl _Mtx_lock(_Mtx_t);
_CRTIMP2_PURE _Thrd_result __cdecl _Mtx_trylock(_Mtx_t);
_CRTIMP2_PURE _Thrd_result __cdecl _Mtx_timedlock(_Mtx_t, const _timespec64*);
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_CRTIMP2_PURE _Thrd_result __cdecl _Mtx_unlock(_Mtx_t); // TRANSITION, ABI: Always succeeds
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_CRTIMP2_PURE void* __cdecl _Mtx_getconcrtcs(_Mtx_t);
_CRTIMP2_PURE void __cdecl _Mtx_clear_owner(_Mtx_t);
_CRTIMP2_PURE void __cdecl _Mtx_reset_owner(_Mtx_t);

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29 changes: 14 additions & 15 deletions stl/src/mutex.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -77,26 +77,28 @@ void _Mtx_destroy(_Mtx_t mtx) { // destroy mutex
}

static _Thrd_result mtx_do_lock(_Mtx_t mtx, const _timespec64* target) { // lock mutex
// TRANSITION, ABI: the use of `const _timespec64*` is preserved for `_Mtx_timedlock`
const long current_thread_id = static_cast<long>(GetCurrentThreadId());
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if ((mtx->_Type & ~_Mtx_recursive) == _Mtx_plain) { // set the lock
if (mtx->_Thread_id != static_cast<long>(GetCurrentThreadId())) { // not current thread, do lock
if (mtx->_Thread_id != current_thread_id) { // not current thread, do lock
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AcquireSRWLockExclusive(get_srw_lock(mtx));
mtx->_Thread_id = static_cast<long>(GetCurrentThreadId());
mtx->_Thread_id = current_thread_id;
}
++mtx->_Count;

return _Thrd_result::_Success;
} else { // handle timed or recursive mutex
int res = WAIT_TIMEOUT;
if (target == nullptr) { // no target --> plain wait (i.e. infinite timeout)
if (mtx->_Thread_id != static_cast<long>(GetCurrentThreadId())) {
if (mtx->_Thread_id != current_thread_id) {
AcquireSRWLockExclusive(get_srw_lock(mtx));
}

res = WAIT_OBJECT_0;

} else if (target->tv_sec < 0 || target->tv_sec == 0 && target->tv_nsec <= 0) {
// target time <= 0 --> plain trylock or timed wait for time that has passed; try to lock with 0 timeout
if (mtx->_Thread_id != static_cast<long>(GetCurrentThreadId())) { // not this thread, lock it
if (mtx->_Thread_id != current_thread_id) { // not this thread, lock it
if (TryAcquireSRWLockExclusive(get_srw_lock(mtx)) != 0) {
res = WAIT_OBJECT_0;
} else {
Expand All @@ -107,11 +109,12 @@ static _Thrd_result mtx_do_lock(_Mtx_t mtx, const _timespec64* target) { // lock
}

} else { // check timeout
// TRANSITION, ABI: this branch is preserved for `_Mtx_timedlock`
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_timespec64 now;
_Timespec64_get_sys(&now);
while (now.tv_sec < target->tv_sec || now.tv_sec == target->tv_sec && now.tv_nsec < target->tv_nsec) {
// time has not expired
if (mtx->_Thread_id == static_cast<long>(GetCurrentThreadId())
if (mtx->_Thread_id == current_thread_id
|| TryAcquireSRWLockExclusive(get_srw_lock(mtx)) != 0) { // stop waiting
res = WAIT_OBJECT_0;
break;
Expand All @@ -123,31 +126,25 @@ static _Thrd_result mtx_do_lock(_Mtx_t mtx, const _timespec64* target) { // lock
}
}

if (res == WAIT_OBJECT_0 || res == WAIT_ABANDONED) {
if (res == WAIT_OBJECT_0) {
if (1 < ++mtx->_Count) { // check count
if ((mtx->_Type & _Mtx_recursive) != _Mtx_recursive) { // not recursive, fixup count
--mtx->_Count;
res = WAIT_TIMEOUT;
}
} else {
mtx->_Thread_id = static_cast<long>(GetCurrentThreadId());
mtx->_Thread_id = current_thread_id;
}
}

switch (res) {
case WAIT_OBJECT_0:
case WAIT_ABANDONED:
if (res == WAIT_OBJECT_0) {
return _Thrd_result::_Success;

case WAIT_TIMEOUT:
} else { // WAIT_TIMEOUT
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if (target == nullptr || (target->tv_sec == 0 && target->tv_nsec == 0)) {
return _Thrd_result::_Busy;
} else {
return _Thrd_result::_Timedout;
}

default:
return _Thrd_result::_Error;
}
}
}
Expand Down Expand Up @@ -178,6 +175,7 @@ _Thrd_result _Mtx_trylock(_Mtx_t mtx) { // attempt to lock try_mutex
return mtx_do_lock(mtx, &xt);
}

// TRANSITION, ABI: preserved for binary compatibility
_Thrd_result _Mtx_timedlock(_Mtx_t mtx, const _timespec64* xt) { // attempt to lock timed mutex
_Thrd_result res;

Expand All @@ -190,6 +188,7 @@ int _Mtx_current_owns(_Mtx_t mtx) { // test if current thread owns mutex
return mtx->_Count != 0 && mtx->_Thread_id == static_cast<long>(GetCurrentThreadId());
}

// TRANSITION, ABI: preserved for binary compatibility
void* _Mtx_getconcrtcs(_Mtx_t mtx) { // get internal cs impl
return &mtx->_Critical_section;
}
Expand Down