Re: Writing a thread-safe class
News123 wrote: So what's recommended way for multicore machines? Threads will probably only accelerate if the used C libraries are releasing the GIL, right? What's for example about PIL (Python Imaging library)? Assuming, that the C library calls don't releas the GIL Shoud I directly use use fork() and some kind of IPC? or are there some special well established, recommendable commodity modules aiming for rmultiprocessor job distribution? So far I have just a single-core machine, but I'll be using a multicore machine in the next weeks. Then I'll probably find out Have a look at the multiprocessing module. bye N sturlamolden wrote: On 12 Sep, 15:54, Timothy Madden wrote: I find that hard to believe, but I will look into it. Carl Banks is correct. There is a mutex called "the global interpreter lock" that takes care of this. You can have multiple threads running, but access to the Python interpreter is serialized. -- http://mail.python.org/mailman/listinfo/python-list
Re: Writing a thread-safe class
So what's recommended way for multicore machines? Threads will probably only accelerate if the used C libraries are releasing the GIL, right? What's for example about PIL (Python Imaging library)? Assuming, that the C library calls don't releas the GIL Shoud I directly use use fork() and some kind of IPC? or are there some special well established, recommendable commodity modules aiming for rmultiprocessor job distribution? So far I have just a single-core machine, but I'll be using a multicore machine in the next weeks. Then I'll probably find out bye N sturlamolden wrote: > On 12 Sep, 15:54, Timothy Madden wrote: > >> I find that hard to believe, but I will look into it. > > Carl Banks is correct. > > There is a mutex called "the global interpreter lock" that takes care > of this. You can have multiple threads running, but access to the > Python interpreter is serialized. > > > -- http://mail.python.org/mailman/listinfo/python-list
Re: Writing a thread-safe class
On 12 Sep, 15:54, Timothy Madden wrote: > I find that hard to believe, but I will look into it. Carl Banks is correct. There is a mutex called "the global interpreter lock" that takes care of this. You can have multiple threads running, but access to the Python interpreter is serialized. -- http://mail.python.org/mailman/listinfo/python-list
Re: Writing a thread-safe class
Carl Banks wrote: [...] You are not correct. Dictionary operation (like getting and setting items) are atomic and limited to one thread at a time, thus thread- safe. > (In fact, in CPython only one thread can execute Python code at a time, in most cases. This is called the Global Interpreter Lock, or [...] I find that hard to believe, but I will look into it. Thank you, Timothy Madden -- http://mail.python.org/mailman/listinfo/python-list
Re: Writing a thread-safe class
On Sep 11, 4:26 pm, Timothy Madden wrote: > Hello > > I would like to write a class with methods that can be accessed by many > threads at the same time. > > For this I have a lock attribute in my class obtained with > threading.Lock(), in the constructor, and every method begins by > acquiring the lock and ends by releasing it > > My problem is that the lock is still an attribute of the class, and the > very expression self.lock in the statement self.lock.acquire() is > performed before locking, thus not being thread-safe. > > If I am correct self is a dictionary of object attributes, and if > another thread has the lock and creates a new attribute, or deletes one, > in the same time with my lookup for self.lock, than the lookup is > compromised. You are not correct. Dictionary operation (like getting and setting items) are atomic and limited to one thread at a time, thus thread- safe. (In fact, in CPython only one thread can execute Python code at a time, in most cases. This is called the Global Interpreter Lock, or GIL. If you search this newsgroup for information you will find a LOT of discission about it. Other Python implementations such as Jython may not use the GIL, but I am quite sure dictionary access is thread- safe on those platforms also.) > How do people create thread-safe classes in python ? I think exactly the way you are doing it. (Some people might use threading.RLock instead as a minor safety measure, but threading.Lock will suffice.) Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
