Method Thread.Mutex()->shared_lock()

Method shared_lock

MutexKey shared_lock()
MutexKey shared_lock(int type)
MutexKey shared_lock(int type, int(0..)|float seconds)
MutexKey shared_lock(int type, int(0..) seconds, int(0..999999999) nanos)

Description

This function attempts to lock the mutex. If the mutex is already locked by a different thread the current thread will sleep until the mutex is unlocked. The value returned is the 'key' to the lock. When the key is destructed or has no more references the mutex will automatically be unlocked.

The type argument specifies what lock() should do if the mutex is already locked exclusively by this thread:

0	Throw an error.
1	Sleep until the mutex is unlocked. Useful if some other thread will unlock it.
2	Return zero. This allows recursion within a locked region of code, but in conjunction with other locks it easily leads to unspecified locking order and therefore a risk for deadlocks.

Parameter seconds

Seconds to wait before the timeout is reached.

Parameter nanos

Nano (1/1000000000) seconds to wait before the timeout is reached. This value is added to the number of seconds specified by seconds.

A timeout of zero seconds disables the timeout.

Returns

Returns a MutexKey on success and 0 (zero) on timeout.

Note

Note that the timeout is approximate (best effort), and may be exceeded if eg the interpreter is busy after the timeout.

Note

Note that if the current thread already holds a shared key, a new will be created without waiting, and regardless of the value of type.

Note

If the mutex is destructed while it's locked or while threads are waiting on it, it will continue to exist internally until the last thread has stopped waiting and the last MutexKey has disappeared, but further calls to the functions in this class will fail as is usual for destructed objects.

Note

Support for shared keys was added in Pike 8.1.

See also

lock(), trylock(), try_shared_lock()