Question

I’m writing to many files in a threaded app and I’m creating one handler per file. I have HandlerFactory class that manages the distribution of these handlers. What I’d like to do is that

thread A requests and gets foo.txt’s file handle from the HandlerFactory class

thread B requests foo.txt’s file handler

handler class recognizes that this file handle has been checked out

handler class puts thread A to sleep

thread B closes file handle using a wrapper method from HandlerFactory

HandlerFactory notifies sleeping threads

thread B wakes and successfully gets foo.txt’s file handle

This is what I have so far,

def get_handler(self, file_path, type):
    self.lock.acquire()
    if file_path not in self.handlers:
        self.handlers[file_path] = open(file_path, type)
    elif not self.handlers[file_path].closed:
        time.sleep(1)
    self.lock.release()
    return self.handlers[file_path][type]

I believe this covers the sleeping and handler retrieval successfully, but I am unsure how to wake up all threads, or even better wake up a specific thread.

Answer 1

What you’re looking for is known as a condition variable.

Condition Variables

Here is the Python 2 library reference.
For Python 3 it can be found here