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#pragma once
#include <util/generic/deque.h>
#include <util/generic/maybe.h>
#include <util/generic/yexception.h>
#include <util/system/condvar.h>
#include <util/system/guard.h>
#include <util/system/mutex.h>
#include <utility>
namespace NThreading {
///
/// TBlockingQueue is a queue of elements of limited or unlimited size.
/// Queue provides Push and Pop operations that block if operation can't be executed
/// (queue is empty or maximum size is reached).
///
/// Queue can be stopped, in that case all blocked operation will return `Nothing` / false.
///
/// All operations are thread safe.
///
///
/// Example of usage:
/// TBlockingQueue<int> queue;
///
/// ...
///
/// // thread 1
/// queue.Push(42);
/// queue.Push(100500);
///
/// ...
///
/// // thread 2
/// while (TMaybe<int> number = queue.Pop()) {
/// ProcessNumber(number.GetRef());
/// }
template <class TElement>
class TBlockingQueue {
public:
///
/// Creates blocking queue with given maxSize
/// if maxSize == 0 then queue is unlimited
TBlockingQueue(size_t maxSize)
: MaxSize(maxSize == 0 ? Max<size_t>() : maxSize)
, Stopped(false)
{
}
///
/// Blocks until queue has some elements or queue is stopped or deadline is reached.
/// Returns `Nothing` if queue is stopped or deadline is reached.
/// Returns element otherwise.
TMaybe<TElement> Pop(TInstant deadline = TInstant::Max()) {
TGuard<TMutex> g(Lock);
const auto canPop = [this]() { return CanPop(); };
if (!CanPopCV.WaitD(Lock, deadline, canPop)) {
return Nothing();
}
if (Stopped && Queue.empty()) {
return Nothing();
}
TElement e = std::move(Queue.front());
Queue.pop_front();
CanPushCV.Signal();
return std::move(e);
}
TMaybe<TElement> Pop(TDuration duration) {
return Pop(TInstant::Now() + duration);
}
///
/// Blocks until queue has space for new elements or queue is stopped or deadline is reached.
/// Returns false exception if queue is stopped and push failed or deadline is reached.
/// Pushes element to queue and returns true otherwise.
bool Push(const TElement& e, TInstant deadline = TInstant::Max()) {
return PushRef(e, deadline);
}
bool Push(TElement&& e, TInstant deadline = TInstant::Max()) {
return PushRef(std::move(e), deadline);
}
bool Push(const TElement& e, TDuration duration) {
return Push(e, TInstant::Now() + duration);
}
bool Push(TElement&& e, TDuration duration) {
return Push(std::move(e), TInstant::Now() + duration);
}
///
/// Stops the queue, all blocked operations will be aborted.
void Stop() {
TGuard<TMutex> g(Lock);
Stopped = true;
CanPopCV.BroadCast();
CanPushCV.BroadCast();
}
///
/// Checks whether queue is empty.
bool Empty() const {
TGuard<TMutex> g(Lock);
return Queue.empty();
}
///
/// Returns size of the queue.
size_t Size() const {
TGuard<TMutex> g(Lock);
return Queue.size();
}
///
/// Checks whether queue is stopped.
bool IsStopped() const {
TGuard<TMutex> g(Lock);
return Stopped;
}
private:
bool CanPush() const {
return Queue.size() < MaxSize || Stopped;
}
bool CanPop() const {
return !Queue.empty() || Stopped;
}
template <typename Ref>
bool PushRef(Ref e, TInstant deadline) {
TGuard<TMutex> g(Lock);
const auto canPush = [this]() { return CanPush(); };
if (!CanPushCV.WaitD(Lock, deadline, canPush)) {
return false;
}
if (Stopped) {
return false;
}
Queue.push_back(std::forward<TElement>(e));
CanPopCV.Signal();
return true;
}
private:
TMutex Lock;
TCondVar CanPopCV;
TCondVar CanPushCV;
TDeque<TElement> Queue;
size_t MaxSize;
bool Stopped;
};
}
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