柚子快報(bào)邀請碼778899分享：C++多線程學(xué)習(xí)04

http://yzkb.51969.com/

參考

參考資料地址：戀戀風(fēng)辰官方博客

判斷是否占有鎖

#include

#include

#include

#include

//unique_lock 基本用法

std::mutex mtx;

int shared_data = 0;

void use_unique()

{

// lock可自動解鎖，也可手動解鎖

std::unique_lock lock(mtx);

std::cout << "use unique lock, lock success" << std::endl;

shared_data++;

lock.unlock();

}

// 可以通過unique_lock的owns_lock判斷是否占有鎖

void owns_lock()

{

std::unique_lock lock(mtx);

shared_data++;

if (lock.owns_lock()) {

std::cout << "owns lock" << std::endl;

}

else {

std::cout << "doesn't own lock" << std::endl;

}

lock.unlock();

if (lock.owns_lock()) {

std::cout << "owns lock" << std::endl;

}

else {

std::cout << "doesn't own lock" << std::endl;

}

}

int main()

{

// 1. 判斷是否占有鎖

owns_lock();

std::cout << "Finished! \n";

}

測試同時使用owns_lock和defer_lock

// 也可以延遲加鎖

void defer_lock()

{

std::unique_lock lock(mtx, std::defer_lock);

lock.lock();

// 這里可以選擇手動解析釋放，也可以等作用域結(jié)束自動釋放

lock.unlock();

}

// 同時使用owns和defer

void use_own_defer()

{

std::unique_lock lock(mtx);

// 判斷是否擁有鎖

if (lock.owns_lock()) {

std::cout << "Main thread has the lock \n";

}

else {

std::cout << "Main thread dose not have the lock \n";

}

std::thread t([]() {

std::unique_lock lock(mtx, std::defer_lock);

if (lock.owns_lock()) {

std::cout << "Thread has the lock \n";

}

else {

std::cout << "Thread dose not have the lock. \n";

}

lock.lock();

if (lock.owns_lock()) {

std::cout << "Thread has the lock. \n";

}

else {

std::cout << "Thread dose not have the lock \n";

}

lock.unlock();

});

t.join();

}

int main()

{

// 2. 測試同時使用owns_lock和defer_lock

use_own_defer();

// 子線程會卡在加鎖的邏輯上, 導(dǎo)致程序阻塞

std::cout << "Finished! \n";

}

unique_lock也支持領(lǐng)養(yǎng)鎖

// unique_lock同樣支持領(lǐng)養(yǎng)

void use_own_adopt()

{

mtx.lock();

std::unique_lock lock(mtx, std::adopt_lock);

if (lock.owns_lock()) {

std::cout << "owns lock" << std::endl;

}

else {

std::cout << "dose not have the lock \n";

}

lock.unlock();

}

int main()

{

// 3. lock_guard一樣，unique_lock也支持領(lǐng)養(yǎng)鎖

// 管理自動釋放

use_own_adopt();

std::cout << "Finished! \n";

}

測試鎖的控制權(quán)轉(zhuǎn)移

// 轉(zhuǎn)移互斥量所有權(quán)

// 互斥量本身不支持move，但是unique_lock支持

std::unique_lock get_lock()

{

std::unique_lock lock(mtx);

shared_data++;

return lock;

}

void use_return()

{

std::unique_lock lock(get_lock());

shared_data++;

}

int main()

{

/*

一旦mutex被unique_lock管理，加鎖和釋放的操作就交給unique_lock，

不能調(diào)用mutex加鎖和解鎖，因?yàn)殒i的使用權(quán)已經(jīng)交給unique_lock.

unique_lock支持移動，當(dāng)一個mutex被轉(zhuǎn)移給unique_lock后，可以通過unique_ptr轉(zhuǎn)移其歸屬權(quán).

*/

// 4. 測試鎖的控制權(quán)轉(zhuǎn)移

use_return();

std::cout << "Finished! \n";

}

測試鎖的粒度

// 測試鎖的粒度

void precision_lock()

{

std::unique_lock lock(mtx);

shared_data++;

lock.unlock();

// 耗時操作不要放在鎖內(nèi)執(zhí)行

std::this_thread::sleep_for(std::chrono::seconds(1));

lock.lock();

shared_data++;

}

int main()

{

/*

鎖的粒度表示加鎖的精細(xì)程度，一個鎖的粒度要足夠大，保證可以鎖住要訪問的共享數(shù)據(jù)。

同時一個鎖的粒度要足夠小，保證非共享數(shù)據(jù)不被鎖住影響性能。

而unique_ptr則很好的支持手動解鎖。

*/

// 5. 測試鎖的粒度

precision_lock();

std::cout << "Finished! \n";

}

測試遞歸鎖

// 遞歸鎖測試

class RecursiveDemo

{

public:

RecursiveDemo()

{

std::cout << "Init Recursive Demo! \n";

}

/* 模擬查詢學(xué)生信息 */

bool QueryStudent(std::string name)

{

std::lock_guard recursive_lock(_recursive_mtx);

#if 0

std::lock_guard recursive_lock(_mtx); // 錯誤用法

#endif

auto iter_find = _students_info.find(name);

if (iter_find == _students_info.end())

return false;

return true;

}

void AddScore(std::string name, int score) {

std::lock_guard recursive_lock(_recursive_mtx);

#if 0

std::lock_guard recursive_lock(_mtx);

#endif

if (!QueryStudent(name)) {

_students_info.insert(std::make_pair(name, score));

return;

}

std::cout << "Add score! Student: " << name << std::endl;

_students_info[name] = _students_info[name] + score;

}

private:

std::map _students_info;

std::recursive_mutex _recursive_mtx;

std::mutex _mtx;

};

// 測試遞歸鎖

void test_recursive()

{

std::shared_ptr stu_demo{ std::make_shared() };

stu_demo->AddScore("Peter", 85);

stu_demo->AddScore("Peter", 85);

}

int main()

{

/*

關(guān)于共享鎖: 讀操作不互斥，讀與寫，寫與寫互斥.

C++ 17標(biāo)準(zhǔn)shared_mutex

C++14提供了 shared_time_mutex

C++11無上述互斥，想使用可以利用boost庫

*/

// 6. 遞歸鎖，嵌套導(dǎo)致卡死

test_recursive();

std::cout << "Finished! \n";

}

柚子快報(bào)邀請碼778899分享：C++多線程學(xué)習(xí)04

http://yzkb.51969.com/

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