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Questions tagged [mutex]

A mutex ("mutual exclusion") is a mechanism to ensure integrity when the same data or resource is accessed (in particular, changed) concurrently from several threads.

A mutex ("mutual exclusion") is a mechanism to ensure integrity when the same data or resource is accessed (in particular, changed) concurrently from several threads.

Usually when the term mutex is used, it refers to a synchronisation primitive functionally identical to a binary semaphore. As OS-level synchronisation is often rather expensive due to context switching, busy-wait solutions based on atomic operations (e.g. mutex or critical section) exist.

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C++11: why does std::condition_variable use std::unique_lock?

I am a bit confused about the role of std::unique_lock when working with std::condition_variable. As far as I understood the documentation, std::unique_lock is basically a bloated lock guard, with the possibility to swap the state between two…
lucas clemente
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pthreads mutex vs semaphore

What is the difference between semaphores and mutex provided by pthread library ?
cppdev
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When is a condition variable needed, isn't a mutex enough?

I'm sure mutex isn't enough that's the reason the concept of condition variables exist; but it beats me and I'm not able to convince myself with a concrete scenario when a condition variable is essential. Differences between Conditional variables,…
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When or why should I use a Mutex over an RwLock?

When I read the documentations of Mutex and RwLock, the difference I see is the following: Mutex can have only one reader or writer at a time, RwLock can have one writer or multiple readers at a time. When you put it that way, RwLock seems always…
Boiethios
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System-wide mutex in Python on Linux

Is there any easy way to have a system-wide mutex in Python on Linux? By "system-wide", I mean the mutex will be used by a group of Python processes; this is in contrast to a traditional mutex, which is used by a group of threads within the same…
emchristiansen
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When to use recursive mutex?

I understand recursive mutex allows mutex to be locked more than once without getting to a deadlock and should be unlocked the same number of times. But in what specific situations do you need to use a recursive mutex? I'm looking for…
jasonline
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understanding of pthread_cond_wait() and pthread_cond_signal()

Generally speaking, pthread_cond_wait() and pthread_cond_signal() are called as below: //thread 1: pthread_mutex_lock(&mutex); pthread_cond_wait(&cond, &mutex); do_something() pthread_mutex_unlock(&mutex); //thread…
user1944267
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Differences between Conditional variables, Mutexes and Locks

For example the c++0x interfaces I am having a hard time figuring out when to use which of these things (cv, mutex and lock). Can anyone please explain or point to a resource? Thanks in advance.
Ronny Brendel
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Why doesn't Mutex get released when disposed?

I have the following code: using (Mutex mut = new Mutex(false, MUTEX_NAME)) { if (mut.WaitOne(new TimeSpan(0, 0, 30))) { // Some code that deals with a specific TCP port // Don't want this to run at the same time in another…
Mike Christensen
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std::mutex vs std::recursive_mutex as class member

I have seen some people hate on recursive_mutex: http://www.zaval.org/resources/library/butenhof1.html But when thinking about how to implement a class that is thread safe (mutex protected), it seems to me excruciatingly hard to prove that every…
NoSenseEtAl
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Synchronising twice on the same object?

I was wondering if in Java I would get any odd behaviour if I synchronise twice on the same object? The scenario is as follows pulbic class SillyClassName { object moo; ... public void method1(){ synchronized(moo) { …
Omar Kooheji
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C++11 equivalent to boost shared_mutex

Is there a C++11 equivalent for the boost::shared_mutex. Or another solution to handle a multiple reader / single writer situation in C++11?
Haatschii
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How do you declare a recursive mutex with POSIX threads?

I am a bit confused on how to declare a recursive mutex using pthread. What I try to do is have only one thread at a time be able to run a piece of code(including functions) but after scepticism I figured out that the use of mutexes would not work…
Pithikos
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Do I need a mutex for reading?

I have a class that has a state (a simple enum) and that is accessed from two threads. For changing state I use a mutex (boost::mutex). Is it safe to check the state (e.g. compare state_ == ESTABLISHED) or do I have to use the mutex in this case…
Tom
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What does std::thread.join() do?

By definition from C++ reference: Blocks the current thread until the thread identified by *this finishes its execution. So does this mean when using .join(), there's no need to mutex.lock() when that thread calls some function? I'm new to mutual…
Guagua
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