/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/*
* w95cv.c -- Windows 95 Machine-Dependent Code for Condition Variables
*
* We implement our own condition variable wait queue. Each thread
* has a semaphore object (thread->md.blocked_sema) to block on while
* waiting on a condition variable.
*
* We use a deferred condition notify algorithm. When PR_NotifyCondVar
* or PR_NotifyAllCondVar is called, the condition notifies are simply
* recorded in the _MDLock structure. We defer the condition notifies
* until right after we unlock the lock. This way the awakened threads
* have a better chance to reaquire the lock.
*/
#include "primpl.h"
/*
* AddThreadToCVWaitQueueInternal --
*
* Add the thread to the end of the condition variable's wait queue.
* The CV's lock must be locked when this function is called.
*/
static void AddThreadToCVWaitQueueInternal(PRThread* thred,
struct _MDCVar* cv) {
PR_ASSERT((cv->waitTail != NULL && cv->waitHead != NULL) ||
(cv->waitTail == NULL && cv->waitHead == NULL));
cv->nwait += 1;
thred->md.inCVWaitQueue = PR_TRUE;
thred->md.next = NULL;
thred->md.prev = cv->waitTail;
if (cv->waitHead == NULL) {
cv->waitHead = thred;
}
else {
cv->waitTail->md.next = thred;
}
cv->waitTail = thred;
}
/*
* md_UnlockAndPostNotifies --
*
* Unlock the lock, and then do the deferred condition notifies.
* If waitThred and waitCV are not NULL, waitThred is added to
* the wait queue of waitCV before the lock is unlocked.
*
* This function is called by _PR_MD_WAIT_CV and _PR_MD_UNLOCK,
* the two places where a lock is unlocked.
*/
static void md_UnlockAndPostNotifies(_MDLock* lock, PRThread* waitThred,
_MDCVar* waitCV) {
PRIntn index;
_MDNotified post;
_MDNotified *notified, *prev = NULL;
/*
* Time to actually notify any conditions that were affected
* while the lock was held. Get a copy of the list that's in
* the lock structure and then zero the original. If it's
* linked to other such structures, we own that storage.
*/
post = lock->notified;
/* a safe copy; we own the lock */
#if defined(DEBUG)
ZeroMemory(&lock->notified,
sizeof(_MDNotified));
/* reset */
#else
lock->notified.length = 0;
/* these are really sufficient */
lock->notified.link = NULL;
#endif
/*
* Figure out how many threads we need to wake up.
*/
notified = &post;
/* this is where we start */
do {
for (index = 0; index < notified->length; ++index) {
_MDCVar* cv = notified->cv[index].cv;
PRThread* thred;
int i;
/* Fast special case: no waiting threads */
if (cv->waitHead == NULL) {
notified->cv[index].notifyHead = NULL;
continue;
}
/* General case */
if (-1 == notified->cv[index].times) {
/* broadcast */
thred = cv->waitHead;
while (thred != NULL) {
thred->md.inCVWaitQueue = PR_FALSE;
thred = thred->md.next;
}
notified->cv[index].notifyHead = cv->waitHead;
cv->waitHead = cv->waitTail = NULL;
cv->nwait = 0;
}
else {
thred = cv->waitHead;
i = notified->cv[index].times;
while (thred != NULL && i > 0) {
thred->md.inCVWaitQueue = PR_FALSE;
thred = thred->md.next;
i--;
}
notified->cv[index].notifyHead = cv->waitHead;
cv->waitHead = thred;
if (cv->waitHead == NULL) {
cv->waitTail = NULL;
}
else {
if (cv->waitHead->md.prev != NULL) {
cv->waitHead->md.prev->md.next = NULL;
cv->waitHead->md.prev = NULL;
}
}
cv->nwait -= notified->cv[index].times - i;
}
}
notified = notified->link;
}
while (NULL != notified);
if (waitThred) {
AddThreadToCVWaitQueueInternal(waitThred, waitCV);
}
/* Release the lock before notifying */
LeaveCriticalSection(&lock->mutex);
notified = &post;
/* this is where we start */
do {
for (index = 0; index < notified->length; ++index) {
PRThread* thred;
PRThread* next;
thred = notified->cv[index].notifyHead;
while (thred != NULL) {
BOOL rv;
next = thred->md.next;
thred->md.prev = thred->md.next = NULL;
rv = ReleaseSemaphore(thred->md.blocked_sema, 1, NULL);
PR_ASSERT(rv != 0);
thred = next;
}
}
prev = notified;
notified = notified->link;
if (&post != prev) {
PR_DELETE(prev);
}
}
while (NULL != notified);
}
/*
* Notifies just get posted to the protecting mutex. The
* actual notification is done when the lock is released so that
* MP systems don't contend for a lock that they can't have.
*/
static void md_PostNotifyToCvar(_MDCVar* cvar, _MDLock* lock,
PRBool broadcast) {
PRIntn index = 0;
_MDNotified* notified = &lock->notified;
while (1) {
for (index = 0; index < notified->length; ++index) {
if (notified->cv[index].cv == cvar) {
if (broadcast) {
notified->cv[index].times = -1;
}
else if (-1 != notified->cv[index].times) {
notified->cv[index].times += 1;
}
return;
}
}
/* if not full, enter new CV in this array */
if (notified->length < _MD_CV_NOTIFIED_LENGTH) {
break;
}
/* if there's no link, create an empty array and link it */
if (NULL == notified->link) {
notified->link = PR_NEWZAP(_MDNotified);
}
notified = notified->link;
}
/* A brand new entry in the array */
notified->cv[index].times = (broadcast) ? -1 : 1;
notified->cv[index].cv = cvar;
notified->length += 1;
}
/*
* _PR_MD_NEW_CV() -- Creating new condition variable
* ... Solaris uses cond_init() in similar function.
*
* returns: -1 on failure
* 0 when it succeeds.
*
*/
PRInt32 _PR_MD_NEW_CV(_MDCVar* cv) {
cv->magic = _MD_MAGIC_CV;
/*
* The waitHead, waitTail, and nwait fields are zeroed
* when the PRCondVar structure is created.
*/
return 0;
}
void _PR_MD_FREE_CV(_MDCVar* cv) {
cv->magic = (PRUint32)-1;
return;
}
/*
* _PR_MD_WAIT_CV() -- Wait on condition variable
*/
void _PR_MD_WAIT_CV(_MDCVar* cv, _MDLock* lock, PRIntervalTime timeout) {
PRThread* thred = _PR_MD_CURRENT_THREAD();
DWORD rv;
DWORD msecs = (timeout == PR_INTERVAL_NO_TIMEOUT)
? INFINITE
: PR_IntervalToMilliseconds(timeout);
/*
* If we have pending notifies, post them now.
*/
if (0 != lock->notified.length) {
md_UnlockAndPostNotifies(lock, thred, cv);
}
else {
AddThreadToCVWaitQueueInternal(thred, cv);
LeaveCriticalSection(&lock->mutex);
}
/* Wait for notification or timeout; don't really care which */
rv = WaitForSingleObject(thred->md.blocked_sema, msecs);
EnterCriticalSection(&(lock->mutex));
PR_ASSERT(rv != WAIT_ABANDONED);
PR_ASSERT(rv != WAIT_FAILED);
PR_ASSERT(rv != WAIT_OBJECT_0 || thred->md.inCVWaitQueue == PR_FALSE);
if (rv == WAIT_TIMEOUT) {
if (thred->md.inCVWaitQueue) {
PR_ASSERT((cv->waitTail != NULL && cv->waitHead != NULL) ||
(cv->waitTail == NULL && cv->waitHead == NULL));
cv->nwait -= 1;
thred->md.inCVWaitQueue = PR_FALSE;
if (cv->waitHead == thred) {
cv->waitHead = thred->md.next;
if (cv->waitHead == NULL) {
cv->waitTail = NULL;
}
else {
cv->waitHead->md.prev = NULL;
}
}
else {
PR_ASSERT(thred->md.prev != NULL);
thred->md.prev->md.next = thred->md.next;
if (thred->md.next != NULL) {
thred->md.next->md.prev = thred->md.prev;
}
else {
PR_ASSERT(cv->waitTail == thred);
cv->waitTail = thred->md.prev;
}
}
thred->md.next = thred->md.prev = NULL;
}
else {
/*
* This thread must have been notified, but the
* ReleaseSemaphore call happens after WaitForSingleObject
* times out. Wait on the semaphore again to make it
* non-signaled. We assume this wait won't take long.
*/
rv = WaitForSingleObject(thred->md.blocked_sema, INFINITE);
PR_ASSERT(rv == WAIT_OBJECT_0);
}
}
PR_ASSERT(thred->md.inCVWaitQueue == PR_FALSE);
return;
}
/* --- end _PR_MD_WAIT_CV() --- */
void _PR_MD_NOTIFY_CV(_MDCVar* cv, _MDLock* lock) {
md_PostNotifyToCvar(cv, lock, PR_FALSE);
return;
}
void _PR_MD_NOTIFYALL_CV(_MDCVar* cv, _MDLock* lock) {
md_PostNotifyToCvar(cv, lock, PR_TRUE);
return;
}
typedef BOOL(WINAPI* INITIALIZECRITICALSECTIONEX)(
CRITICAL_SECTION* lpCriticalSection, DWORD dwSpinCount, DWORD Flags);
static INITIALIZECRITICALSECTIONEX sInitializeCriticalSectionEx;
void _PR_MD_INIT_LOCKS(
void) {
/*
* Starting with Windows Vista, every CRITICAL_SECTION allocates an extra
* RTL_CRITICAL_SECTION_DEBUG object. Unfortunately, this debug object is
* not reclaimed by DeleteCriticalSection(), causing an apparent memory
* leak. This is a debugging "feature", not a bug. If we are running on
* Vista or later, use InitializeCriticalSectionEx() to allocate
* CRITICAL_SECTIONs without debug objects.
*/
HMODULE hKernel32 = GetModuleHandle(
"kernel32.dll");
PR_ASSERT(hKernel32);
PR_ASSERT(!sInitializeCriticalSectionEx);
sInitializeCriticalSectionEx = (INITIALIZECRITICALSECTIONEX)GetProcAddress(
hKernel32,
"InitializeCriticalSectionEx");
}
/*
* By default, CRITICAL_SECTIONs are initialized with a spin count of 0.
* Joe Duffy's "Concurrent Programming on Windows" book suggests 1500 is
* a "reasonable starting point". On single-processor systems, the spin
* count is ignored and the critical section spin count is set to 0.
*/
#define LOCK_SPIN_COUNT 1500
PRStatus _PR_MD_NEW_LOCK(_MDLock* lock) {
CRITICAL_SECTION* cs = &lock->mutex;
BOOL ok;
if (sInitializeCriticalSectionEx) {
ok = sInitializeCriticalSectionEx(cs, LOCK_SPIN_COUNT,
CRITICAL_SECTION_NO_DEBUG_INFO);
}
else {
ok = InitializeCriticalSectionAndSpinCount(cs, LOCK_SPIN_COUNT);
}
if (!ok) {
_PR_MD_MAP_DEFAULT_ERROR(GetLastError());
return PR_FAILURE;
}
lock->notified.length = 0;
lock->notified.link = NULL;
return PR_SUCCESS;
}
void _PR_MD_UNLOCK(_MDLock* lock) {
if (0 != lock->notified.length) {
md_UnlockAndPostNotifies(lock, NULL, NULL);
}
else {
LeaveCriticalSection(&lock->mutex);
}
}
