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ThreadPool: Improve exception handling

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In particular, process() won't return as long as there are active
items. This prevents work item lambdas from referring to stack frames
that no longer exist.
This commit is contained in:
Eelco Dolstra 2017-09-08 14:40:27 +02:00
parent a2740c9ca2
commit 8f6b347abd
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GPG key ID: 8170B4726D7198DE
2 changed files with 53 additions and 24 deletions
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75
src/libutil/thread-pool.cc
View file

@ -46,11 +46,17 @@ void ThreadPool::enqueue(const work_t & t)
void ThreadPool::process()
{
/* Loop until there are no active work items *and* there either
are no queued items or there is an exception. The
post-condition is that no new items will become active. */
while (true) {
auto state(state_.lock());
if (state->exception)
std::rethrow_exception(state->exception);
if (state->left.empty() && !state->pending) break;
if (!state->active) {
if (state->exception)
std::rethrow_exception(state->exception);
if (state->left.empty())
break;
}
state.wait(done);
}
}
@ -58,41 +64,64 @@ void ThreadPool::process()
void ThreadPool::workerEntry()
{
bool didWork = false;
std::exception_ptr exc;
while (true) {
work_t w;
{
auto state(state_.lock());
if (didWork) {
assert(state->active);
state->active--;
if (exc) {
if (!state->exception) {
state->exception = exc;
// Tell the other workers to quit.
state->quit = true;
work.notify_all();
} else {
/* Print the exception, since we can't
propagate it. */
try {
std::rethrow_exception(exc);
} catch (std::exception & e) {
if (!dynamic_cast<Interrupted*>(&e) &&
!dynamic_cast<ThreadPoolShutDown*>(&e))
ignoreException();
} catch (...) {
}
}
}
}
/* Wait until a work item is available or another thread
had an exception or we're asked to quit. */
while (true) {
if (state->quit || state->exception) return;
if (didWork) {
assert(state->pending);
state->pending--;
didWork = false;
if (state->quit) {
if (!state->active)
done.notify_one();
return;
}
if (!state->left.empty()) break;
if (!state->pending)
done.notify_all();
if (!state->active) {
done.notify_one();
return;
}
state.wait(work);
}
w = state->left.front();
w = std::move(state->left.front());
state->left.pop();
state->pending++;
state->active++;
}
try {
w();
} catch (std::exception & e) {
auto state(state_.lock());
if (state->exception) {
if (!dynamic_cast<Interrupted*>(&e) &&
!dynamic_cast<ThreadPoolShutDown*>(&e))
printError(format("error: %s") % e.what());
} else {
state->exception = std::current_exception();
work.notify_all();
done.notify_all();
}
} catch (...) {
exc = std::current_exception();
}
didWork = true;

2
src/libutil/thread-pool.hh
View file

@ -44,7 +44,7 @@ private:
struct State
{
std::queue<work_t> left;
size_t pending = 0;
size_t active = 0;
std::exception_ptr exception;
std::vector<std::thread> workers;
bool quit = false;