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Threaded DNS: Handle spurious wakeups

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As DarthGandalf noticed, POSIX allows spurious wakeups from pthread_cond_wait.

Signed-off-by: Uli Schlachter <psychon@znc.in>
This commit is contained in:
Uli Schlachter
2012-02-19 12:13:25 +01:00
parent 8863d853c9
commit 252e6d7151
2 changed files with 20 additions and 5 deletions
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20
src/Socket.cpp
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@@ -56,6 +56,15 @@ public:
}
};
bool CSockManager::ThreadNeeded(struct TDNSStatus* threadStatus)
{
// We should keep a number of idle threads alive
if (threadStatus->num_idle > MAX_IDLE_THREADS)
return false;
// If ZNC is shutting down, all threads should exit
return !threadStatus->done;
}
void* CSockManager::TDNSThread(void* argument) {
TDNSStatus *threadStatus = (TDNSStatus *) argument;
@@ -63,18 +72,19 @@ void* CSockManager::TDNSThread(void* argument) {
threadStatus->num_threads++;
threadStatus->num_idle++;
while (true) {
/* Wait for a DNS job for us to do */
if (threadStatus->jobs.empty()) {
if (threadStatus->num_idle > MAX_IDLE_THREADS)
/* Wait for a DNS job for us to do. This is a while()-loop
* because POSIX allows spurious wakeups from pthread_cond_wait.
*/
while (threadStatus->jobs.empty()) {
if (!ThreadNeeded(threadStatus))
break;
pthread_cond_wait(&threadStatus->cond, &threadStatus->mutex);
}
if (threadStatus->done)
if (!ThreadNeeded(threadStatus))
break;
/* Figure out a DNS job to do */
assert(!threadStatus->jobs.empty());
assert(threadStatus->num_idle > 0);
TDNSArg *job = threadStatus->jobs.front();
threadStatus->jobs.pop_front();