8000 fix potential spurious wakeups in scheduler code by jsteemann · Pull Request #9770 · arangodb/arangodb · GitHub
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fix potential spurious wakeups in scheduler code #9770

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Merged
merged 1 commit into from
Aug 21, 2019
Merged

fix potential spurious wakeups in scheduler code #9770

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fix potential spurious wakeups in scheduler code
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@jsteemann
jsteemann committed Aug 20, 2019
commit 865e864b618acf5474177b06c83d1102c1999711
53 changes: 27 additions & 26 deletions arangod/Scheduler/SupervisedScheduler.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -317,22 +317,24 @@ void SupervisedScheduler::runWorker() {
id = _numWorkers++; // increase the number of workers here, to obtain the id
// copy shared_ptr with worker state
state = _workerStates.back();
// inform the supervisor that this thread is alive
_conditionSupervisor.notify_one();
}

state->_sleepTimeout_ms = 20 * (id + 1);
// cap the timeout to some boundary value
if (state->_sleepTimeout_ms >= 1000) {
state->_sleepTimeout_ms = 1000;
}
state->_sleepTimeout_ms = 20 * (id + 1);
// cap the timeout to some boundary value
if (state->_sleepTimeout_ms >= 1000) {
state->_sleepTimeout_ms = 1000;
}

if (id < 32U) {
// 512 >> 32 => undefined behavior
state->_queueRetryCount = (uint64_t(512) >> id) + 3;
} else {
// we want at least 3 retries
state->_queueRetryCount = 3;
if (id < 32U) {
// 512 >> 32 => undefined behavior
state->_queueRetryCount = (uint64_t(512) >> id) + 3;
} else {
// we want at least 3 retries
state->_queueRetryCount = 3;
}

// inform the supervisor that this thread is alive
state->_ready = true;
_conditionSupervisor.notify_one();
}

while (true) {
Expand Down Expand Up @@ -548,16 +550,21 @@ void SupervisedScheduler::startOneThread() {
#pragma warning(pop)
#endif

if (!_workerStates.back()->start()) {
auto& state = _workerStates.back();

if (!state->start()) {
// failed to start a worker
_workerStates.pop_back(); // pop_back deletes shared_ptr, which deletes thread
LOG_TOPIC("913b5", ERR, Logger::THREADS)
<< "could not start additional worker thread";

} else {
LOG_TOPIC("f9de8", TRACE, Logger::THREADS) << "Started new thread";
_conditionSupervisor.wait(guard);
return;
}

// sync with runWorker()
_conditionSupervisor.wait(guard, [&state]() {
return state->_ready;
});
LOG_TOPIC("f9de8", TRACE, Logger::THREADS) << "Started new thread";
}

void SupervisedScheduler::stopOneThread() {
Expand Down Expand Up @@ -590,18 +597,12 @@ void SupervisedScheduler::stopOneThread() {
}
}

SupervisedScheduler::WorkerState::WorkerState(SupervisedScheduler::WorkerState&& that) noexcept
: _queueRetryCount(that._queueRetryCount),
_sleepTimeout_ms(that._sleepTimeout_ms),
_stop(that._stop.load()),
_working(false),
_thread(std::move(that._thread)) {}

SupervisedScheduler::WorkerState::WorkerState(SupervisedScheduler& scheduler)
: _queueRetryCount(100),
_sleepTimeout_ms(100),
_stop(false),
_working(false),
_ready(false),
_thread(new SupervisedSchedulerWorkerThread(scheduler)) {}

bool SupervisedScheduler::WorkerState::start() { return _thread->start(); }
Expand Down
7 changes: 6 additions & 1 deletion arangod/Scheduler/SupervisedScheduler.h
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Expand Up @@ -114,12 +114,17 @@ class SupervisedScheduler final : public Scheduler {
uint64_t _queueRetryCount; // t1
uint64_t _sleepTimeout_ms; // t2
std::atomic<bool> _stop, _working;
// _ready = false means the Worker is not properly initialized
// _ready = true means it is initialized and can be used to dispatch tasks to
// _ready is protected by the Scheduler's condition variable & mutex
bool _ready;
clock::time_point _lastJobStarted;
std::unique_ptr<SupervisedSchedulerWorkerThread> _thread;

// initialize with harmless defaults: spin once, sleep forever
explicit WorkerState(SupervisedScheduler& scheduler);
WorkerState(WorkerState&& that) noexcept;
WorkerState(WorkerState const&) = delete;
WorkerState& operator=(WorkerState const&) = delete;

// cppcheck-suppress missingOverride
bool start();
Expand Down
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