8000 BTS-519: avoid holding 2 mutexes at the same time by jsteemann · Pull Request #14511 · arangodb/arangodb · GitHub
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BTS-519: avoid holding 2 mutexes at the same time #14511

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Merged
merged 2 commits into from
Jul 16, 2021
Merged

BTS-519: avoid holding 2 mutexes at the same time #14511

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ebd0c38
BTS-519: avoid holding 2 mutexes at the same time
jsteemann Jul 16, 2021
eba5b34
one more change to reduce holding the global _mutex
jsteemann Jul 16, 2021
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one more change to reduce holding the global _mutex
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@jsteemann
jsteemann committed Jul 16, 2021
commit eba5b34f94c36e05719eb75567aee7a7e529001c
2 changes: 2 additions & 0 deletions arangod/Pregel/Conductor.h
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Expand Up @@ -151,6 +151,8 @@ class Conductor : public std::enable_shared_from_this<Conductor> {
}

bool canBeGarbageCollected() const;

uint64_t executionNumber() const { return _executionNumber; }

private:
void cancelNoLock();
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37 changes: 26 additions & 11 deletions arangod/Pregel/PregelFeature.cpp
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Expand Up @@ -335,19 +335,34 @@ std::shared_ptr<Conductor> PregelFeature::conductor(uint64_t executionNumber) {

void PregelFeature::garbageCollectConductors() try {
// iterate over all conductors and remove the ones which can be garbage-collected
MUTEX_LOCKER(guard, _mutex);
for (auto it = _conductors.begin(); it != _conductors.end(); /*no hoisting*/) {
if (it->second.conductor->canBeGarbageCollected()) {
uint64_t executionNumber = it->first;

it->second.conductor->cancel();
it = _conductors.erase(it);

_workers.erase(executionNumber);
} else {
++it;
std::vector<std::shared_ptr<Conductor>> conductors;

// copy out shared-ptrs of Conductors under the mutex
{
MUTEX_LOCKER(guard, _mutex);
for (auto const& it : _conductors) {
if (it.second.conductor->canBeGarbageCollected()) {
if (conductors.empty()) {
conductors.reserve(8);
}
conductors.emplace_back(it.second.conductor);
}
}
}

// cancel and kill conductors without holding the mutex
// permanently
for (auto& c : conductors) {
c->cancel();
}

MUTEX_LOCKER(guard, _mutex);
for (auto& c : conductors) {
uint64_t executionNumber = c->executionNumber();

_conductors.erase(executionNumber);
_workers.erase(executionNumber);
}
} catch (...) {}

void PregelFeature::addWorker(std::shared_ptr<IWorker>&& w, uint64_t executionNumber) {
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