Foreword: Resource sharing between threads, so there is no communication problem, but there will be a strong competition problem. There are several ways to solve the competition problem between threads:
1. Mutex
Function: Ensure that only one thread can operate on shared resources at the same time, but synchronization is not guaranteed
step:
1.1 Initialize the mutex: (2 methods, generally used static)
Dynamic initialization:
static pthread_mutex_t mm;
prhread_mutex_init(&mm,NULL)；
Static initialization:
static pthread_mutex_t mm=PTHREAD_MUTEX_INITIALIZER;
1.2 Add/unlock operation
pthread_mutex_lock(&mm); //Lock operation, the thread that has not acquired the lock will block and wait
pthread_mutex_trylock(&mm) //Lock operation, the thread that has not acquired the lock will return non-zero, and continue to execute other non-competitive tasks
pthread_mutex_unlock(&mm) //Unlock operation, the unlock operation will not go wrong, it can be unlocked even if there is no lock
1.3 Destroying a mutex (lock)
pthread_mutex_destroy(&mm)//
2. Read-write lock: read-shared and write-exclusive
Function: Sometimes when multiple threads need to read and write the same resource, there may be problems such as data loss. For example, a read event occurs when writing, and the read-write lock can effectively ensure read sharing and write exclusive . It is mainly used for There are both reads and writes, and the number of reads is much greater than that of writes
Note: Each thread should give up its own time slice after execution, which can solve the problem of thread starvation
sched_yield() //Abandon cpu scheduling
step:
2.1 Initialize read-write locks (dynamic initialization only)
static pthread_rwlock_t rw;//Declare a global lock variable
pthread_rwlock_init(&rw,NULL) //Initialize the lock
2.2 Add/Unlock
pthread_rwlock_wrlock(&rw); //Add a write lock, if the lock fails, it will be blocked here
pthread_rwlock_trywrlock(&rw) ; //Add a write lock, if the lock fails, it will immediately return a non-zero value to perform other work
pthread_rwlock_rdlock(&rw); //Add a read lock, fail to block
pthread_rwlock_tryrdlock(&rw); //Add read lock, fail non-blocking
pthread_rwlock_unlock(&rw); //Unlock (no type and will not fail)
2.3 Destroying locks
pthread_rwlock_ destroy(&rw);
3. Condition variables