C++ 多线程 读锁之后不能跟写锁 shared_lock之后不能跟unique_lock 死锁 解决方案

#include <iostream>
#include <boost/thread/mutex.hpp>
#include <boost/thread/thread.hpp>

boost::shared_mutex mutex;
int count = 0;

void test(int j){
    // boost::shared_lock<boost::shared_mutex> lock(mutex);
    boost::unique_lock<boost::shared_mutex> lock(mutex);

    std::cout << "test == " << j << std::endl;
}

void Counter() {

  int i = count;
  std::cout << "count == " << i << std::endl;
  boost::shared_lock<boost::shared_mutex> lock(mutex);
  test(count++);

}



int main() {

  boost::thread_group threads;

  for (int i = 0; i < 4; ++i) {
    threads.create_thread(&Counter);
  }

  threads.join_all();
  return 0;
}

写锁得等所有读锁释放之后，才能获得锁。可是每个子线程都持有读锁，并且不释放，所以造成死锁。

解决方案

用完锁就释放

#include <iostream>
#include <boost/thread/mutex.hpp>
#include <boost/thread/thread.hpp>

boost::shared_mutex mutex;
int count = 0;

void test(int j){
    // boost::shared_lock<boost::shared_mutex> lock(mutex);
    boost::unique_lock<boost::shared_mutex> lock(mutex);

    std::cout << "test == " << j << std::endl;
}

void Counter() {

  int i = count;
  std::cout << "count == " << i << std::endl;
    {
        boost::shared_lock<boost::shared_mutex> lock(mutex);
    }
  test(count++);

}



int main() {

  boost::thread_group threads;

  for (int i = 0; i < 4; ++i) {
    threads.create_thread(&Counter);
  }

  threads.join_all();
  return 0;
}