/* Add or remove an asynchronous tickee. If periodms is non zero add the
* tickee, calling it every periodms.
*
* N.B. addHighPriorityTickee is called from the VM thread, whereas
* checkHighPriorityTickees is called from the high-priority heartbeat thread
* (or an interrupt). The above 64-bit variables must therefore be read and
* written atomically to avoid either thread reading or writing a modified
* half of the variable while the other half has yet to be updated.
*/
void
addHighPriorityTickee(void (*tickee)(void), unsigned periodms)
{
int i;
if (!periodms) {
for (i = 0; i < numAsyncTickees; i++)
/* We cannot safely copy the data to keep used tickees contiguous
* because checkHighPriorityTickees could be called during the move.
* This implies first checking for an existing tickee below before
* using an empty slot because an empty slot can be created before
* a used (and subsequently modified) tickee.
*/
if (async[i].tickee == tickee) {
async[i].tickee = 0;
sqLowLevelMFence();
return;
}
return;
}
for (i = 0; i < numAsyncTickees; i++)
if (async[i].tickee == tickee)
break;
if (i >= numAsyncTickees)
for (i = 0; i < NUM_ASYNCHRONOUS_TICKEES; i++)
if (i >= numAsyncTickees
|| !async[i].tickee)
break;
if (i >= NUM_ASYNCHRONOUS_TICKEES)
error("ran out of asyncronous tickee slots");
/* first disable the tickee while updating the entry. */
async[i].tickee = 0;
sqLowLevelMFence();
async[i].tickeePeriodUsecs = periodms * MicrosecondsPerMillisecond;
async[i].tickeeDeadlineUsecs = async[i].tickeePeriodUsecs
+ ioUTCMicroseconds();
async[i].inProgress = 0;
async[i].tickee = tickee;
if (i >= numAsyncTickees)
++numAsyncTickees;
sqLowLevelMFence();
}
static inline void lockSignalQueue()
{
volatile int old;
/* spin to obtain a lock */
do {
sqLowLevelMFence();
sqCompareAndSwapRes(sigLock, 0, 1, old );
} while (old != 0);
}
void
checkHighPriorityTickees(usqLong utcMicrosecondClock)
{
int i;
#if ITIMER_HEARTBEAT
extern void unblockVMThreadAfterYieldToHighPriorityTickerThread(void);
shouldYieldToHighPriorityTickerThread = 1;
#endif
/* Since this runs either in a high-priority thread or in an interrupt only
* one fence is needed. Since the VM thread will not disturb any non-zero
* entry (except for changing the period) we can read the entry without
* locking. But we need to lock the attempt to run the tickee in case for
* any reason checkHighPriorityTickees is miscalled reentrantly.
*/
sqLowLevelMFence();
for (i = 0; i < numAsyncTickees; i++)
if (async[i].tickee
&& !async[i].inProgress
&& utcMicrosecondClock >= async[i].tickeeDeadlineUsecs) {
int previousInProgress;
sqCompareAndSwapRes(async[i].inProgress,0,1,previousInProgress);
if (previousInProgress == 0) {
assert(async[i].inProgress);
if (async[i].tickeeDeadlineUsecs + HiccupThreshold
< utcMicrosecondClock)
async[i].tickeeDeadlineUsecs
= utcMicrosecondClock + async[i].tickeePeriodUsecs;
else
async[i].tickeeDeadlineUsecs
+= async[i].tickeePeriodUsecs;
async[i].tickee();
async[i].inProgress = 0;
}
}
#if ITIMER_HEARTBEAT
shouldYieldToHighPriorityTickerThread = 0;
sqLowLevelMFence();
unblockVMThreadAfterYieldToHighPriorityTickerThread();
#endif
}
void
hptick(void)
{
unsigned long long start = ioUTCMicroseconds();
yield = 1;
sqLowLevelMFence();
while (ioUTCMicroseconds() - start < hptickusecs)
if ((hpcount += 1ULL) % CHECK_COUNT == 0
&& ioHeartbeatFrequency(0) == 0)
lockedup("in hptick");
yield = 0;
sqLowLevelMFence();
if (yieldMethod == yield_via_wait_signal) {
if (pthread_mutex_trylock(&yield_sync) == 0) {/* success */
pthread_mutex_unlock(&yield_sync);
not_blocked_count += 1;
}
else {
pthread_cond_signal(&yield_cond);
unblock_count += 1;
}
}
}
void
ioSynchronousCheckForEvents()
{
int i;
#if ITIMER_HEARTBEAT
extern void yieldToHighPriorityTickerThread(void);
sqLowLevelMFence();
if (shouldYieldToHighPriorityTickerThread)
yieldToHighPriorityTickerThread();
#endif
for (i = 0; i < numSyncTickees; i++)
if (synch[i].tickee
&& ioUTCMicroseconds() >= synch[i].tickeeDeadlineUsecs) {
synch[i].tickeeDeadlineUsecs += synch[i].tickeePeriodUsecs;
synch[i].tickee();
}
}
/* Signal the external semaphore with the given index. Answer non-zero on
* success, zero otherwise. This function is (should be) thread-safe;
* multiple threads may attempt to signal the same semaphore without error.
* An index of zero should be and is silently ignored.
*
* (sig) As well as negative index.
*/
sqInt
signalSemaphoreWithIndex(sqInt index)
{
int next;
/* An index of zero should be and is silently ignored. */
if (index <=0)
return 0;
/* we must use the locking semantics to avoid ABA problem on writing a semaphore index to queue,
so there is no chance for fetching thread to observe queue in inconsistent state.
*/
lockSignalQueue();
/* check for queue overflow */
next = succIndex(sigIndexHigh);
if (next == sigIndexLow ) {
#if SQ_DYNAMIC_QUEUE_SIZE
// grow and retry
unlockSignalQueue();
ioGrowSignalQueue( maxPendingSignals + 100);
return signalSemaphoreWithIndex(index);
#else
unlockSignalQueue();
// error if queue size is static (perhaps better would be to sleep for a while and retry?)
error("External semaphore signal queue overflow");
#endif
}
signalQueue[sigIndexHigh] = index;
/* make sure semaphore index is written before we advance sigIndexHigh */
sqLowLevelMFence();
sigIndexHigh = next;
/* reset lock */
unlockSignalQueue();
forceInterruptCheck();
return 1;
}
void
maybeYield()
{
sqLowLevelMFence();
if (!yield)
return;
yield_count += 1;
switch (yieldMethod) {
case no_yield: break;
case yield_via_sched_yield:
sched_yield();
break;
case yield_via_pthread_yield:
pthread_yield();
break;
case yield_via_nanosleep: {
struct timespec yieldtime;
yieldtime.tv_sec = 0;
yieldtime.tv_nsec = 10 * 1000;
break;
}
case yield_via_cond_timedwait: {
struct timespec yieldtime;
yieldtime.tv_sec = 0;
yieldtime.tv_nsec = 10 * 1000;
pthread_cond_timedwait(&yield_cond, &yield_mutex, &yieldtime);
break;
}
case yield_via_wait_signal: { int err;
if ((err = pthread_mutex_lock(&yield_mutex))) {
if (err != EDEADLK)
fprintf(stderr,"pthread_mutex_lock yield_mutex %s\n", strerror(err));
}
else if ((err = pthread_mutex_lock(&yield_sync))) {
if (err != EDEADLK)
fprintf(stderr,"pthread_mutex_lock yield_sync %s\n", strerror(err));
}
else {
sqLowLevelMFence();
if (yield
&& (err = pthread_cond_wait(&yield_cond, &yield_mutex)))
fprintf(stderr,"pthread_cond_wait %s\n", strerror(err));
}
break;
}
default:
fprintf(stderr,"unrecognized yield method\n");
exit(5);
}
}
