Boost C++ Libraries

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Class file_lock

boost::interprocess::file_lock

Synopsis

// In header: <boost/interprocess/sync/file_lock.hpp>


class file_lock {
public:
  // construct/copy/destruct
  file_lock() noexcept;
  file_lock(const char *);
  file_lock(const wchar_t *);
  file_lock(file_lock &&) noexcept;
  file_lock & operator=(file_lock &&) noexcept;
  ~file_lock();

  // public member functions
  void swap(file_lock &) noexcept;
  void lock();
  bool try_lock();
  template<typename TimePoint> bool timed_lock(const TimePoint &);
  void unlock();
  void lock_sharable();
  bool try_lock_sharable();
  template<typename TimePoint> bool timed_lock_sharable(const TimePoint &);
  void unlock_sharable();
};

Description

A file lock, is a mutual exclusion utility similar to a mutex using a file. A file lock has sharable and exclusive locking capabilities and can be used with scoped_lock and sharable_lock classes. A file lock can't guarantee synchronization between threads of the same process so just use file locks to synchronize threads from different processes.

file_lock public construct/copy/destruct

  1. file_lock() noexcept;

    Constructs an empty file mapping. Does not throw

  2. file_lock(const char * name);

    Opens a file lock. Throws interprocess_exception if the file does not exist or there are no operating system resources.

  3. file_lock(const wchar_t * name);

    Opens a file lock. Throws interprocess_exception if the file does not exist or there are no operating system resources.

    Note: This function is only available on operating systems with native wchar_t APIs (e.g. Windows).

  4. file_lock(file_lock && moved) noexcept;

    Moves the ownership of "moved"'s file mapping object to *this. After the call, "moved" does not represent any file mapping object. Does not throw

  5. file_lock & operator=(file_lock && moved) noexcept;

    Moves the ownership of "moved"'s file mapping to *this. After the call, "moved" does not represent any file mapping. Does not throw

  6. ~file_lock();
    Closes a file lock. Does not throw.

file_lock public member functions

  1. void swap(file_lock & other) noexcept;

    Swaps two file_locks. Does not throw.

  2. void lock();

    Requires: The calling thread does not own the mutex.

    Effects: The calling thread tries to obtain exclusive ownership of the mutex, and if another thread has exclusive, or sharable ownership of the mutex, it waits until it can obtain the ownership. Throws: interprocess_exception on error.

    Note: A program may deadlock if the thread that has ownership calls this function. If the implementation can detect the deadlock, an exception could be thrown.

  3. bool try_lock();

    Requires: The calling thread does not own the mutex.

    Effects: The calling thread tries to acquire exclusive ownership of the mutex without waiting. If no other thread has exclusive, or sharable ownership of the mutex this succeeds. Returns: If it can acquire exclusive ownership immediately returns true. If it has to wait, returns false. Throws: interprocess_exception on error.

    Note: A program may deadlock if the thread that has ownership calls this function. If the implementation can detect the deadlock, an exception could be thrown.

  4. template<typename TimePoint> bool timed_lock(const TimePoint & abs_time);

    Requires: The calling thread does not own the mutex.

    Effects: The calling thread tries to acquire exclusive ownership of the mutex waiting if necessary until no other thread has exclusive, or sharable ownership of the mutex or abs_time is reached. Returns: If acquires exclusive ownership, returns true. Otherwise returns false. Throws: interprocess_exception on error.

    Note: A program may deadlock if the thread that has ownership calls this function. If the implementation can detect the deadlock, an exception could be thrown.

  5. void unlock();

    Precondition: The thread must have exclusive ownership of the mutex. Effects: The calling thread releases the exclusive ownership of the mutex. Throws: An exception derived from interprocess_exception on error.

  6. void lock_sharable();

    Requires: The calling thread does not own the mutex.

    Effects: The calling thread tries to obtain sharable ownership of the mutex, and if another thread has exclusive ownership of the mutex, waits until it can obtain the ownership. Throws: interprocess_exception on error.

    Note: A program may deadlock if the thread that owns a mutex object calls this function. If the implementation can detect the deadlock, an exception could be thrown.

  7. bool try_lock_sharable();

    Effects: The calling thread tries to acquire sharable ownership of the mutex without waiting. If no other thread has exclusive ownership of the mutex this succeeds. Returns: If it can acquire sharable ownership immediately returns true. If it has to wait, returns false. Throws: interprocess_exception on error.

  8. template<typename TimePoint> 
      bool timed_lock_sharable(const TimePoint & abs_time);

    Effects: The calling thread tries to acquire sharable ownership of the mutex waiting if necessary until no other thread has exclusive ownership of the mutex or abs_time is reached. Returns: If acquires sharable ownership, returns true. Otherwise returns false. Throws: interprocess_exception on error.

  9. void unlock_sharable();

    Precondition: The thread must have sharable ownership of the mutex. Effects: The calling thread releases the sharable ownership of the mutex. Throws: An exception derived from interprocess_exception on error.


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