object which offers a convenient means of parallelizing the execution of a function across multiple input values, distributing the input data across processes (data parallelism).The following example demonstrates the common practice of defining such functions in a module so that child processes can successfully import that module.Once a process or thread has acquired a recursive lock, the same process or thread may acquire it again without blocking; that process or thread must release it once for each time it has been acquired.Note that , block until the lock is in an unlocked state (not owned by any process or thread) unless the lock is already owned by the current process or thread.Similarly, if the process has acquired a lock or semaphore etc.then terminating it is liable to cause other processes to deadlock.
Without one, the functionality in this class will be disabled, and attempts to instantiate a Warning If a process is killed while it is trying to read or write to a pipe then the data in the pipe is likely to become corrupted, because it may become impossible to be sure where the message boundaries lie. Once a process or thread has acquired a lock, subsequent attempts to acquire it from any process or thread will block until it is released; any process or thread may release it. A recursive lock must be released by the process or thread that acquired it.
By default if a process is not the creator of the queue then on exit it will attempt to join the queue’s background thread. It is likely to cause enqueued data to lost, and you almost certainly will not need to use it.
It is really only there if you need the current process to exit immediately without waiting to flush enqueued data to the underlying pipe, and you don’t care about lost data.
This means that if you try joining that process you may get a deadlock unless you are sure that all items which have been put on the queue have been consumed.
Similarly, if the child process is non-daemonic then the parent process may hang on exit when it tries to join all its non-daemonic children.
All resources of the parent are inherited by the child process. The fork server process is single threaded so it is safe for it to use process which tracks the unlinked named semaphores created by processes of the program.
Note that safely forking a multithreaded process is problematic. When all processes have exited the semaphore tracker unlinks any remaining semaphores.
Usually there should be none, but if a process was killed by a signal there may be some “leaked” semaphores.
(Unlinking the named semaphores is a serious matter since the system allows only a limited number, and they will not be automatically unlinked until the next reboot.) To select a start method you use the As mentioned above, when doing concurrent programming it is usually best to avoid using shared state as far as possible.
When a process first puts an item on the queue a feeder thread is started which transfers objects from a buffer into the pipe.
The usual Indicate that no more data will be put on this queue by the current process.