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/*
* Author: Sven Gothel <sgothel@jausoft.com>
* Copyright (c) 2021 Gothel Software e.K.
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
#ifndef JAU_LATCH_HPP_
#define JAU_LATCH_HPP_
#include <cstdint>
#include <mutex>
#include <condition_variable>
#include <jau/ordered_atomic.hpp>
namespace jau {
/**
* Inspired by std::latch of C++20
*
* @see https://en.cppreference.com/w/cpp/thread/latch
*/
class latch {
private:
mutable std::mutex mtx_cd;
mutable std::mutex mtx_cv;
mutable std::condition_variable cv;
jau::sc_atomic_size_t count;
public:
/** Returns the maximum value of the internal counter supported by the implementation. */
static constexpr size_t max() noexcept { return std::numeric_limits<size_t>::max(); }
/**
* Initialize instance with given counter.
*
* Compatible with std::latch.
*
* @param count_
*/
latch(const size_t count_) noexcept
: count(count_) {}
/**
* No copy constructor nor move constructor.
*
* Compatible with std::latch.
*
* @param o
*/
latch(const latch& o) = delete;
/**
* Return the current atomic internal counter.
*
* Extension of std::latch.
*/
size_t value() const noexcept { return count; }
/**
* Atomically decrements the internal counter by n
* and notifies all blocked wait() threads if zero is reached.
*
* If n is greater than the value of the internal counter, the counter is set to zero.
*
* This operation strongly happens-before all calls that are unblocked on this latch.
*
* Compatible with std::latch.
*
* @param n the value by which the internal counter is decreased, defaults to 1
*/
void count_down(const size_t n = 1) noexcept {
bool notify;
{
std::unique_lock<std::mutex> lock(mtx_cd); // Avoid data-race on concurrent count_down() calls
if( n < count ) {
count = count - n;
notify = false;
} else {
count = 0;
notify = true;
}
}
if( notify ) {
cv.notify_all();
}
}
/**
* Returns true only if the internal counter has reached zero.
*
* Compatible with std::latch.
*/
bool try_wait() const noexcept {
return 0 == count;
}
/**
* Blocks the calling thread until the internal counter reaches 0.
*
* If the internal counter is zero already, returns immediately.
*
* Compatible with std::latch.
*/
void wait() const noexcept {
if( 0 < count ) {
std::unique_lock<std::mutex> lock(mtx_cv);
while( 0 < count ) {
cv.wait(lock);
}
}
}
/**
* Atomically decrements the internal counter by n and (if necessary) blocks the calling thread until the counter reaches zero.
*
* Equivalent to `count_down(n); wait();`.
*
* Compatible with std::latch.
*
* @param n the value by which the internal counter is decreased, defaults to 1
*/
void arrive_and_wait(const size_t n = 1) noexcept {
count_down(n);
wait();
}
/**
* Blocks the calling thread until the internal counter reaches 0 or the given timeout duration has expired.
*
* If the internal counter is zero already, returns immediately.
*
* Implementation uses `std::chrono::steady_clock::now()`.
*
* Extension of std::latch.
*
* @tparam Rep
* @tparam Period
* @param timeout_duration maximum time duration to spend waiting
* @return true if internal counter has reached zero, otherwise a timeout has occurred.
*/
template<typename Rep, typename Period>
bool wait_for(const std::chrono::duration<Rep, Period>& timeout_duration) const noexcept {
if( 0 < count ) {
std::unique_lock<std::mutex> lock(mtx_cv);
while( 0 < count ) {
std::chrono::steady_clock::time_point t0 = std::chrono::steady_clock::now();
std::cv_status s = cv.wait_until(lock, t0 + timeout_duration);
if( std::cv_status::timeout == s && 0 < count ) {
return false;
}
}
}
return true;
}
/**
* Blocks the calling thread until the internal counter reaches 0 or the given timeout duration has expired.
*
* If the internal counter is zero already, returns immediately.
*
* Implementation uses `std::chrono::steady_clock::now()`.
*
* Extension of std::latch.
*
* @param timeout_ms maximum time duration to spend waiting in milliseconds
* @return true if internal counter has reached zero, otherwise a timeout has occurred.
*/
bool wait_for(const size_t timeout_ms) const noexcept {
return wait_for(std::chrono::milliseconds(timeout_ms));
}
/**
* Atomically decrements the internal counter by n and (if necessary) blocks the calling thread until the counter reaches zero
* or the given timeout duration has expired.
*
* Equivalent to `count_down(n); wait(timeout_duration);`.
*
* Implementation uses `std::chrono::steady_clock::now()`.
*
* Extension of std::latch.
*
* @tparam Rep
* @tparam Period
* @param timeout_duration maximum time duration to spend waiting
* @param n the value by which the internal counter is decreased, defaults to 1
* @return true if internal counter has reached zero, otherwise a timeout has occurred.
*/
template<typename Rep, typename Period>
bool arrive_and_wait_for(const std::chrono::duration<Rep, Period>& timeout_duration, const size_t n = 1) noexcept {
count_down(n);
return wait_for(timeout_duration);
}
/**
* Atomically decrements the internal counter by n and (if necessary) blocks the calling thread until the counter reaches zero
* or the given timeout duration has expired.
*
* Equivalent to `count_down(n); wait(timeout_duration);`.
*
* Implementation uses `std::chrono::steady_clock::now()`.
*
* Extension of std::latch.
*
* @param timeout_ms maximum time duration to spend waiting in milliseconds
* @param n the value by which the internal counter is decreased, defaults to 1
* @return true if internal counter has reached zero, otherwise a timeout has occurred.
*/
bool arrive_and_wait_for(const size_t timeout_ms, const size_t n = 1) noexcept {
return arrive_and_wait_for(std::chrono::milliseconds(timeout_ms), n);
}
};
} /* namespace jau */
#endif /* JAU_LATCH_HPP_ */
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