CODEWITHSUNDEEP
pythonmultithreadingsemaphoreblocking
Adam
Adam

Reputation: 125

Python2.6.5 : Is there python equivalent of Java Semaphore tryAcquire

I am looking for python alternative for Java's tryAcquire Semaphore function. I found out that this function is added in python version 3 and after. I am using python version 2.6.5. Any alternatives for me ? Only thing I have here is semaphore.acquire(blocking=False) This is my code in Java - (semaphore release is being done in another thread whose code i have not included)

if(Sem.tryAcquire(30, TimeUnit.SECONDS))   
   log.info("testCall Semaphore acquired ");
else 
   log.error("Semaphore Timeout occured");

Upvotes: 1

Views: 811

Answers (1)

lvc
lvc

Reputation: 35089

Semaphore is implemented in pure Python - see http://hg.python.org/cpython/file/3.3/Lib/threading.py , starting at line 236. The acquire method is implemented this way:

def acquire(self, blocking=True, timeout=None):
    if not blocking and timeout is not None:
        raise ValueError("can't specify timeout for non-blocking acquire")
    rc = False
    endtime = None
    with self._cond:
        while self._value == 0:
            if not blocking:
                break
            if timeout is not None:
                if endtime is None:
                    endtime = _time() + timeout
                else:
                    timeout = endtime - _time()
                    if timeout <= 0:
                        break
            self._cond.wait(timeout)
        else:
            self._value = self._value - 1
            rc = True
    return rc

self._cond is a Condition wrapping a Lock.

You could use Semaphore's technique directly in your code instead of using the class, but it would probably be easier to copy the entire class into your own code. If forward compatibility is an issue, you could even condition it out like so:

from threading import *
from sys import version_info

if version_info < (3, 2):
    # Need timeout in Semaphore.acquire,
    # from Python 3.3 threading.py
    class Semaphore:
        ...

Whichever way you do this, you will also need the new Condition class - according to the docs for Condition.wait,

The return value is True unless a given timeout expired, in which case it is False.

Changed in version 3.2: Previously, the method always returned None.

The Semaphore timeout code relies on this behavior. The rabbit hole doesn't appear to go any deeper than that, but, your easiest solution might even be to copy the entire 3.3 threading.py, make any changes it needs to run on 2.x, and add a prominent comment at the top that you're deliberately shadowing the stdlib.

Upvotes: 1

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