C ++ 11 threads lock_gurad

The mutex 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:

• 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.

Mutex class is a synchronization primitives can be used to protect shared data from multiple threads access.

Mutex provides exclusive, non-recursive ownership semantics:

From a successful call to lock or unlock try_lock until the call date, the calling thread owns a mutex.
When a thread owns a mutex, if all other threads trying to claim ownership of the mutex, they will block (used to call lock) or receive an error return value (for try_lock).
Before calling lock or try_lock, the calling thread can not own the mutex.
It is destroyed if a mutex is still owned by any thread, or a thread has terminated when a mutex, the behavior of the program is uncertain. Mutex Mutex class and meets all requirements of StandardLayoutType.

std :: mutex neither copied nor moved.

lock:locks the mutex, blocks if the mutex is not available;

Mutex lock, if the mutex is not available, blocking

try_lock

tries to lock the mutex, returns if the mutex is not available

 Trying to lock a mutex mutex is not available, then returns

unlock unlocks the mutex

native_handle return to baseline achieved native handle object definition

Usually do not directly access the std :: mutex: std :: unique_lock, std :: lock_guard or std :: scoped_lock (starting from C ++ 17) in a more secure way to manage abnormal lock.

Example
This example shows how to use the mutex to protect shared between two threads std :: map.

// threadTest.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
#include <iostream>
#include <map>
#include <string>
#include <chrono>
#include <thread>
#include <mutex>
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 &pair : g_pages) {
		std::cout << pair.first << " => " << pair.second << '\n';
	}
    return 0;
}