mutex.hpp

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#pragma once
 
/// @file userver/engine/mutex.hpp
/// @brief @copybrief engine::Mutex
 
#include <atomic>
#include <chrono>
#include <mutex>  // for std locks
 
#include <userver/engine/deadline.hpp>
#include <userver/engine/impl/wait_list_fwd.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace engine {
 
/// @ingroup userver_concurrency
///
/// @brief std::mutex replacement for asynchronous tasks.
///
/// Ignores task cancellations (succeeds even if the current task is cancelled).
///
/// ## Example usage:
///
/// @snippet engine/mutex_test.cpp  Sample engine::Mutex usage
///
/// @see @ref scripts/docs/en/userver/synchronization.md
class Mutex final {
public:
    Mutex();
    ~Mutex();
 
    Mutex(const Mutex&) = delete;
    Mutex(Mutex&&) = delete;
    Mutex& operator=(const Mutex&) = delete;
    Mutex& operator=(Mutex&&) = delete;
 
    /// Locks the mutex. Blocks current task if the mutex is locked by
    /// another task. Throws if a task tries to lock a mutex
    /// which is already locked by the current task.
    ///
    /// @note The method waits for the mutex even if the current task is
    /// cancelled.
    void lock();
 
    /// Unlocks the mutex. Before calling this method the mutex should be locked by the current task.
    ///
    /// @note the order of tasks to unblock is unspecified. Any code assuming
    /// any specific order (e.g. FIFO) is incorrect and should be fixed.
    void unlock();
 
    /// Tries to lock the mutex without blocking the task, returns true if succeeded.
    ///
    /// @note The behavior of the function is not affected by the cancellation
    /// requests.
    [[nodiscard]] bool try_lock() noexcept;
 
    /// Tries to lock the mutex in specified duration. Blocks current task if
    /// the mutex is locked by another task up to the provided duration.
    /// Throws if a task tries to lock a mutex which is already locked by the current task.
    ///
    /// @returns true if the locking succeeded
    ///
    /// @note The method waits for the mutex even if the current task is
    /// cancelled.
    template <typename Rep, typename Period>
    [[nodiscard]] bool try_lock_for(const std::chrono::duration<Rep, Period>&);
 
    /// Tries to lock the mutex till specified time point. Blocks current
    /// task if the mutex is locked by another task up to the provided
    /// time point. Throws if a task tries to lock a mutex which is already locked by the current task.
    ///
    /// @returns true if the locking succeeded
    ///
    /// @note The method waits for the mutex even if the current task is
    /// cancelled.
    template <typename Clock, typename Duration>
    [[nodiscard]] bool try_lock_until(const std::chrono::time_point<Clock, Duration>&);
 
    /// @overload
    [[nodiscard]] bool try_lock_until(Deadline deadline);
 
private:
    class Impl;
 
    utils::FastPimpl<Impl, 96, alignof(void*)> impl_;
};
 
template <typename Rep, typename Period>
bool Mutex::try_lock_for(const std::chrono::duration<Rep, Period>& duration) {
    return try_lock_until(Deadline::FromDuration(duration));
}
 
template <typename Clock, typename Duration>
bool Mutex::try_lock_until(const std::chrono::time_point<Clock, Duration>& until) {
    return try_lock_until(Deadline::FromTimePoint(until));
}
 
}  // namespace engine
 
USERVER_NAMESPACE_END