Here’s some code for my future reference on how to use QMutex or QMutexLocker.<\/p>\n
Lessons Learned:
\n * Use QMutex to protect data, not code. Try not to lock hughe amounts of code within a function with mutex.lock(), mutex.unlock(), if for any reason you forget to release the lock you’ll be in trouble. Use the mutex directly only when you know what it is that you want to protect concurrent access from.
\n * When you have a complex function and you don’t want to worry about what to protect and when to release the lock (on exceptions thrown, before returns,etc), you can create an instance of QMutexLocker and it should release the mutex lock upon destruction… this takes us to the next lesson
\n * When using a QMutexLocker, DO NOT make the QMutexLocker an attribute of your class, otherwise, the reference will live after the method finishes and the lock won’t be released.<\/p>\n
Here’s some code.<\/p>\n
\nfrom PyQt4.Qt import QObject, QMutex, QApplication, QThread, QMutexLocker\nimport sys\n\nclass MutexTestSubject(QObject):\n\t'''\n\tClass that uses a QMutex to synchronize\n access to its add(),substract() methods.\n\n This works perfectly fine.\n\t'''\n\tdef __init__(self):\n\t\tQObject.__init__(self)\n\t\tself.MAX_LIMIT = 100\n\t\tself.MIN_LIMIT = 0\n\t\tself.counter = 50\n\t\tself.mutex = QMutex()\n\n\tdef add(self):\n\t\tself.mutex.lock()\n\t\tif self.counter < self.MAX_LIMIT:\n\t\t\tself.counter = self.counter + 1\n\t\tself.mutex.unlock()\n\n\tdef substract(self):\n\t\tself.mutex.lock()\n\t\tif self.counter > self.MIN_LIMIT:\n\t\t\tself.counter = self.counter - 1\n\t\tself.mutex.unlock()\n\n\tdef printStatus(self,thread):\n\t\tprint \"Counter:\",self.counter,\" - Thread:\",id(thread)\n\n\t\tif self.counter > self.MAX_LIMIT+1 or self.counter < self.MIN_LIMIT:\n\t\t\tprint \"Stopping Threads, Max Surpassed, Not Thread Safe. Last Thread:\",id(thread)\n\t\t\tsys.exit()\n\t\n\nclass MutexLockerTestSubject(QObject):\n\t'''\n\tClass that attemps to synchronize thread\n \taccess to its add(),substract() methods with\n\tthe QMutexLocker object.\n\t'''\n\tdef __init__(self):\n\t\tQObject.__init__(self)\n\t\tself.MAX_LIMIT = 100\n\t\tself.MIN_LIMIT = 0\n\t\tself.counter = 50\n\t\tself.mutex = QMutex()\n\n\tdef add(self):\n\t\t#VIP: DO NOT MAKE mutexLocker an attribute of your class.\n\t\t#other wise it won't be destroyed and the lock will never be released.\n\t\tmutexLocker = QMutexLocker(self.mutex)\n\t\tif self.counter < self.MAX_LIMIT:\n\t\t\tself.counter = self.counter + 1\n\n\tdef substract(self):\n\t\tmutexLocker = QMutexLocker(self.mutex)\n\t\tif self.counter > self.MIN_LIMIT:\n\t\t\tself.counter = self.counter - 1\n\n\tdef printStatus(self,thread):\n\t\tprint \"Counter:\",self.counter,\" - Thread:\",id(thread)\n\n\t\tif self.counter > self.MAX_LIMIT+1 or self.counter < self.MIN_LIMIT:\n\t\t\tprint \"Stopping Threads, Max Surpassed, Not Thread Safe. Last Thread:\",id(thread)\n\t\t\tsys.exit()\n\n\nclass AdderWorker(QThread):\n\tdef __init__(self, mutexTestObject):\n\t\tself.mutexTestObject = mutexTestObject\n\t\tQThread.__init__(self)\n\n\tdef run(self):\n\t\twhile(True):\n\t\t\tself.mutexTestObject.add()\n\t\t\tself.mutexTestObject.printStatus(self)\n\nclass SubstractorWorker(QThread):\n\tdef __init__(self, mutexTestObject):\n\t\tself.mutexTestObject = mutexTestObject\n\t\tQThread.__init__(self,mutexTestObject)\n\n\tdef run(self):\n\t\twhile(True):\n\t\t\tself.mutexTestObject.substract()\n\t\t\tself.mutexTestObject.printStatus(self)\n\nif __name__ == \"__main__\":\n\tUSE_MUTEX_LOCKER = True #switch this to use regular mutexes vd QMutexLocker\n\tapp = QApplication(sys.argv)\n\tmutexTestObject = MutexTestSubject() if not USE_MUTEX_LOCKER else MutexLockerTestSubject()\n\n\tadderThread = AdderWorker(mutexTestObject)\n\tsubstracterThread = SubstractorWorker(mutexTestObject)\n\n\tadderThread.start()\n\tsubstracterThread.start()\n\n\tsys.exit(app.exec_())\n<\/pre>\n","protected":false},"excerpt":{"rendered":"Here’s some code for my future reference on how to use QMutex or QMutexLocker. Lessons Learned: * Use QMutex to protect data, not code. Try not to lock hughe amounts of code within a function with mutex.lock(), mutex.unlock(), if for any reason you forget to release the lock you’ll be in trouble. Use the mutex […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2}},"categories":[15,65,66],"tags":[820],"class_list":["post-611","post","type-post","status-publish","format-standard","hentry","category-code","category-python","category-qt4","tag-python-qt4-pyqt3-mutex-qmutex-qmutexlocker"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p5Unzf-9R","jetpack-related-posts":[{"id":650,"url":"https:\/\/www.gubatron.com\/blog\/checking-what-pyqt4-version-youre-running\/","url_meta":{"origin":611,"position":0},"title":"Checking what PyQt4 version you’re running","author":"gubatron","date":"February 1, 2008","format":false,"excerpt":"This is one of those things I tend to forget >>> PyQt4.Qt.qVersion() '4.3.3'","rel":"","context":"In "Code"","block_context":{"text":"Code","link":"https:\/\/www.gubatron.com\/blog\/category\/code\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":788,"url":"https:\/\/www.gubatron.com\/blog\/blooploader-06-is-hardy-compatible\/","url_meta":{"origin":611,"position":1},"title":"Blooploader 0.6 is Hardy compatible","author":"gubatron","date":"April 26, 2008","format":false,"excerpt":"Blooploader 0.6 running on Hardy. 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If for some odd reason you\u2026","rel":"","context":"In "Code"","block_context":{"text":"Code","link":"https:\/\/www.gubatron.com\/blog\/category\/code\/"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":1946,"url":"https:\/\/www.gubatron.com\/blog\/reviewing-the-nokia-n900-user-and-developer-opinions\/","url_meta":{"origin":611,"position":5},"title":"Reviewing the Nokia N900, User and Developer opinions.","author":"gubatron","date":"July 7, 2010","format":false,"excerpt":"Playing with it from the User Perspective - Virtual keyboard is deactivated by default, not good if you have one hand busy, however I can see why it's this way (the virtual keyboard sucks). 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