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| Member functions | ||||
| Locking | ||||
| Native handle | ||||
Defined in header <mutex> | ||
class mutex; | (since C++11) | |
Themutex class is a synchronization primitive that can be used to protect shared data from being simultaneously accessed by multiple threads.
mutex offers exclusive, non-recursive ownership semantics:
mutex from the time that it successfully calls eitherlock ortry_lock until it callsunlock.mutex, all other threads will block (for calls tolock) or receive afalse return value (fortry_lock) if they attempt to claim ownership of themutex.mutex prior to callinglock ortry_lock.The behavior of a program is undefined if amutex is destroyed while still owned by any threads, or a thread terminates while owning amutex. Themutex class satisfies all requirements ofMutex andStandardLayoutType.
std::mutex is neither copyable nor movable.
Contents |
| Name | Definition |
native_handle_type(optional*) | implementation-defined[edit] |
| constructs the mutex (public member function)[edit] | |
| destroys the mutex (public member function)[edit] | |
operator= [deleted] | not copy-assignable (public member function)[edit] |
Locking | |
| locks the mutex, blocks if the mutex is not available (public member function)[edit] | |
| tries to lock the mutex, returns if the mutex is not available (public member function)[edit] | |
| unlocks the mutex (public member function)[edit] | |
Native handle | |
| returns the underlying implementation-defined native handle object (public member function)[edit] | |
std::mutex is usually not accessed directly:std::unique_lock,std::lock_guard,orstd::scoped_lock(since C++17) manage locking in a more exception-safe manner.
This example shows how amutex can be used to protect anstd::map shared between two threads.
#include <chrono>#include <iostream>#include <map>#include <mutex>#include <string>#include <thread> std::map<std::string,std::string> g_pages;std::mutex g_pages_mutex; void save_page(conststd::string& url){// simulate a long page fetchstd::this_thread::sleep_for(std::chrono::seconds(2));std::string result="fake content"; std::lock_guard<std::mutex> guard(g_pages_mutex); g_pages[url]= result;} int main(){std::thread t1(save_page,"http://foo");std::thread t2(save_page,"http://bar"); t1.join(); t2.join(); // safe to access g_pages without lock now, as the threads are joinedfor(constauto&[url, page]: g_pages)std::cout<< url<<" => "<< page<<'\n';}
Output:
http://bar => fake contenthttp://foo => fake content
(C++11) | provides mutual exclusion facility which can be locked recursively by the same thread (class)[edit] |
(C++11) | implements a strictly scope-based mutex ownership wrapper (class template)[edit] |
(C++11) | implements movable mutex ownership wrapper (class template)[edit] |
(C++17) | deadlock-avoiding RAII wrapper for multiple mutexes (class template)[edit] |
(C++11) | provides a condition variable associated with astd::unique_lock (class)[edit] |
