Reader writer mode

When writing multithreading, there is a situation that is more common. That is, there are fewer opportunities for public data modification . Rather than rewrite, they read more opportunities.

Reader-writer mode: Three relationships, two types of people, one place

Three types of relationships:

Readers and readers: no relationship

Written and written by: mutual exclusion

Reader and Writer: synchronization and mutual exclusion

Two types of people: Reader, writer

One place: the same critical resource (data)

Spin Lock: If the waiting condition is not satisfied, does not hang, always apply for the lock. It is appropriate for a thread to occupy a shorter lock time.

When there are more and more readers ready to read, if there is a writer arrives, at this time should be the current reader after reading, improve the writer priority, the next entry into the critical section is the writer. ---------Write is preferable, otherwise it will cause the writer to starve.

When there are more than one writer ready to write, if a reader arrives, at this time should be the current writer after writing, improve the reader priority, the next entry into the critical section is the reader. ---------readers first, otherwise it will cause the reader to starve

Read-write lock correlation function:

#include <pthread.h>

int Pthread_rwlock_destroy (pthread_rwlock_t *rwlock);

int Pthread_rwlock_init (pthread_rwlock_t *restrict Rwlock,

Const pthread_rwlockattr_t *restrict attr);

int Pthread_rwlock_trywrlock (pthread_rwlock_t *rwlock);

int Pthread_rwlock_wrlock (pthread_rwlock_t *rwlock);//write First

int Pthread_rwlock_rdlock (pthread_rwlock_t *rwlock);//Reader preference

int Pthread_rwlock_tryrdlock (pthread_rwlock_t *rwlock);

#include <stdio.h> #include <pthread.h>int g_val=0;pthread_rwlock_t rw_lock;void*  Reader (Void* arg) {    while (1)     {         pthread_rwlock_rdlock (&rw_lock);         printf (" G_val: %d\n ", g_val);         pthread_rwlock_unlock (&rw_lock);     }}void* writer (Void* arg) {    while (1)      {        sleep (1);//enable the writer to compete once every second lock resources          pthread_rwlock_wrlock (&rw_lock);        g_val++;         pthread_rwlock_unlock (&rw_lock);     }} Int main () {    pthread_t tid1,tid2;    pthread_rwlock_init ( &rw_lock,null);     pthread_create (&tid1,null,reader,null);     pthread_create ( &tid2,null,writer,null);     pthread_rwlock_destroy (&rw_lock);     pthread_join (Tid1,null);     pthread_join (tid2,null);     return  0;}

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Reader writer mode