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读写锁#xff08;Read-Write Lock#xff09;是一种并发控制机制#xff0c;用于多线程环境中实现对共享资源的高效读写操作。读写锁允许多个线程同时读取共享资源#xff0c;但在有写操作时#xff0c;需要互斥地独占对共享资源的访问#xff0c;以确保数据的…一、简介
读写锁Read-Write Lock是一种并发控制机制用于多线程环境中实现对共享资源的高效读写操作。读写锁允许多个线程同时读取共享资源但在有写操作时需要互斥地独占对共享资源的访问以确保数据的一致性。
二、shared_mutex
std::shared_mutex 是 C17 引入的用于实现共享/独占访问控制以下是简单示例
#include iostream
#include thread
#include shared_mutexstd::shared_mutex rwLock;
int sharedData 0; // 共享资源void readerFunction(int id) {while (true) {rwLock.lock_shared();std::cout Reader id reads sharedData: sharedData std::endl;rwLock.unlock_shared();// 模拟一些耗时操作std::this_thread::sleep_for(std::chrono::milliseconds(500));}
}void writerFunction(int id) {while (true) {rwLock.lock();sharedData;std::cout Writer id writes sharedData: sharedData std::endl;rwLock.unlock();// 模拟一些耗时操作std::this_thread::sleep_for(std::chrono::milliseconds(1000));}
}int main() {const int numReaders 3;const int numWriters 3;std::thread readers[numReaders];std::thread writers[numWriters];// 启动线程for (int i 0; i numReaders; i) {readers[i] std::thread(readerFunction, i);}for (int i 0; i numWriters; i) {writers[i] std::thread(writerFunction, i);}// Join线程for (int i 0; i numReaders; i) {readers[i].join();}for (int i 0; i numWriters; i) {writers[i].join();}return 0;
}三、自定义 ReadWriteLock
C17前可以通过 mutex 和 condition_variable 实现一个自定义的读写锁。代码如下
#include mutex
#include condition_variableclass ReadWriteLock {
public:ReadWriteLock() : readersCount(0), writing(false) {}void lockRead() {std::unique_lockstd::mutex lock(mutex_);readCondition_.wait(lock, [this] { return !writing; });readersCount;}void unlockRead() {std::unique_lockstd::mutex lock(mutex_);readersCount--;if (readersCount 0) {writeCondition_.notify_one();}}void lockWrite() {std::unique_lockstd::mutex lock(mutex_);writeCondition_.wait(lock, [this] { return readersCount 0 !writing; });writing true;}void unlockWrite() {std::unique_lockstd::mutex lock(mutex_);writing false;readCondition_.notify_all();writeCondition_.notify_one();}private:std::mutex mutex_;std::condition_variable readCondition_;std::condition_variable writeCondition_;int readersCount;bool writing;
};使用示例
#include iostream
#include thread
#include ReadWriteLock.hpp // 包含上面ReadWriteLock的头文件int sharedData 0; // 共享数据
ReadWriteLock rwLock;void readerFunction(int id) {while (true) {rwLock.lockRead();std::cout Reader id reads sharedData: sharedData std::endl;rwLock.unlockRead();// 模拟一些耗时操作std::this_thread::sleep_for(std::chrono::milliseconds(500));}
}void writerFunction(int id) {while (true) {rwLock.lockWrite();sharedData;std::cout Writer id writes sharedData: sharedData std::endl;rwLock.unlockWrite();// 模拟一些耗时操作std::this_thread::sleep_for(std::chrono::milliseconds(1000));}
}int main() {const int numReaders 3;const int numWriters 3;std::thread readers[numReaders];std::thread writers[numWriters];// 启动线程for (int i 0; i numReaders; i) {readers[i] std::thread(readerFunction, i);}for (int i 0; i numWriters; i) {writers[i] std::thread(writerFunction, i);}// Join线程for (int i 0; i numReaders; i) {readers[i].join();}for (int i 0; i numWriters; i) {writers[i].join();}return 0;
}
