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std::mutex(3)		       C++ Standard Libary		   std::mutex(3)

NAME
     std::mutex - std::mutex

Synopsis
	Defined in header <mutex>
	class mutex;		   (since C++11)

	The  mutex class is a synchronization primitive that can be used to pro-
     tect shared
	data from being simultaneously accessed by multiple threads.

	mutex offers exclusive, non-recursive ownership semantics:

	  * A calling thread owns a mutex from the  time  that	it  successfully
     calls either
	    lock or try_lock until it calls unlock.
	  *  When a thread owns a mutex, all other threads will block (for calls
     to lock) or
	    receive a false return value (for try_lock) if they attempt to claim
     ownership
	    of the mutex.
	  * A calling thread must not own the mutex prior  to  calling	lock  or
     try_lock.

	The  behavior  of  a  program is undefined if a mutex is destroyed while
     still owned by
	any threads, or a thread terminates while  owning  a  mutex.  The  mutex
     class satisfies
	all requirements of Mutex and StandardLayoutType.

	std::mutex is neither copyable nor movable.

Member functions
	constructor   constructs the mutex
		      (public member function)
	destructor    destroys the mutex
		      (public member function)
	operator=     not copy-assignable
	[deleted]     (public member function)

Locking
	lock	      locks the mutex, blocks if the mutex is not available
		      (public member function)
	try_lock       tries  to  lock	the  mutex,  returns if the mutex is not
     available
		      (public member function)
	unlock	      unlocks the mutex
		      (public member function)

Native handle
	native_handle returns the underlying implementation-defined native  han-
     dle object
		      (public member function)

Notes
	std::mutex   is   usually   not   accessed  directly:  std::unique_lock,
     std::lock_guard,
	or std::scoped_lock
	(since C++17) manage locking in a more exception-safe manner.

Example
	This example shows how a mutex can be used to protect an std::map shared
     between two
	threads.

     // Run this code

      #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(const std::string& url)
      {
	  // simulate a long page fetch
	  std::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 joined
	  for (const auto& [url, page] : g_pages)
	      std::cout << url << " => " << page << '\n';
      }

Output:
      http://bar => fake content
      http://foo => fake content

See also
	recursive_mutex    provides  mutual  exclusion	facility  which  can  be
     locked
	(C++11) 	   recursively by the same thread
			   (class)
	lock_guard	    implements	a  strictly  scope-based mutex ownership
     wrapper
	(C++11) 	   (class template)
	unique_lock	   implements movable mutex ownership wrapper
	(C++11) 	   (class template)
	scoped_lock	   deadlock-avoiding RAII wrapper for multiple mutexes
	(C++17) 	   (class template)
	condition_variable provides  a	condition  variable  associated  with  a
     std::unique_lock
	(C++11) 	   (class)

http://cppreference.com 	   2024.06.10			   std::mutex(3)
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