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POpython - ensure script is activated only once
 

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    <p>I'm writing a <code>Python 2.7</code> script.<br/> In summary, this script is being run every night on <code>Linux</code> and activates several processes.</p> <p>I'd like to ensure this script is not run multiple times in parallel (basically trying to mimic <code>Singleton</code> pattern but on application level) .</p> <p><em><strong>Code Example</em></strong></p> <pre><code>def main(): # before doing anything, I'd like to know whether this # script was activated and alive. # if so, error out # do something if __name__ == "__main__": main() </code></pre> <p><em><strong>Suggestion</em></strong></p> <p>The naive solution would be to create some kind of a lock file, that acts as a mutex.<br/> The first thing we do is to check whether this file exists. if so, then other instance of the script already created it and we should error out. when the script is done, we remove this file.<br/> I'm assuming this solution would work, as long as the operations on the file system are atomic. </p> <p><em><strong>Implementation</em></strong></p> <pre><code>import os, sys lock_file_path = ".lock_script" def lock_mutex(): if os.path.exists(lock_mutex_path): print "Error: script was already activated." sys.exit(-1) else: file = open(lock_mutex_path, 'w') def unlock_mutex(): assert( os.path.exists(lock_mutex_path)) os.remove(lock_mutex_path) def main(): try: lock_mutex() # do something unlock_mutex() except: unlock_mutex() if __name__ == "__main__": main() </code></pre> <p><em><strong>Problem</em></strong></p> <p>How to ensure <code>lock_mutex()</code> and <code>unlock_mutex()</code> are atomic?</p>
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    1. COYou do not want to invoke script if it is working already right?
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    2. COOut of curiosity, how is the script started such that this is a concern?
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    3. COI don't think your solution is a *naive* solution. In fact, it is quite common for one to create a lock file to check if the script is running.
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