"Linux Advanced Programming" (12th) Linux multithreaded Programming 3

Conditional variable communication mechanism

Conditional variables must implement mutually exclusive access to the resource together with the mutex

How to use:

int Pthread_cond_init (pthread_cond_t *__restrict __cond, __const pthread_condattr_t *__restrict __cond_attr) : initializes a condition variable, the second argument is a Property object, and Null is the default

int Pthread_cond_destroy (pthread_cond_t *__cond) : destroy condition variable

int pthread_cond_signal (pthread_cond_t *__cond) : notifies the first thread of the wait condition variable , which does not work if there are no waiting threads

int Pthread_cond_broadcast (pthread_cond_t *__cond) : notifies all threads waiting for a condition variable , if there is no waiting thread, it does not work

int pthread_cond_wait (pthread_cond_t *__restrict __cond, pthread_mutex_t *__restrict __mutex) : Wait condition variable , the second argument points to the mutex pointer associated with the condition variable

int pthread_cond_timewait (pthread_cond_t *__restrict __cond, pthread_mutex_t *__restrict __mutex, __const struct Timespec *__restrict __ Abstime) : waits for a condition variable within a specified time .

When an online routines waits for a condition variable to enter a wait state, its requested mutex is freed. When you wait for a condition variable, you implicitly request the mutex

Conditional variables implement read-write locks

#include <stdio.h>#include<stdlib.h>#include<time.h>#include"pthread.h"#defineBuffer_size 2//conditional information Structure Bodystructprodcons{intBuffer[buffer_size];//Production Product Valuepthread_mutex_tLock;//Mutual exclusion Lock    intReadpos, Writepos;//Read and write locationspthread_cond_t Notempty;//condition variable, table non-emptypthread_cond_t Notfull;//condition variable, table is not full};//InitializevoidInitstructProdcons *prod) {Pthread_mutex_init (&prod->Lock, NULL); Pthread_cond_init (&prod->Notempty, NULL); Pthread_cond_init (&prod->Notfull, NULL); Prod->readpos =0; Prod->writepos =0;}//Enter a data in the buffervoidPutstructProdcons * PROD,intdata) {    //Lock MutexPthread_mutex_lock (&prod->Lock);  while((Prod->writepos +1)% Buffer_size = = Prod->readpos)//test whether the space is full note that the position of the writepos here to add 1 is to ensure that the next write location is empty?? {printf ("producer wait for not full\n"); Pthread_cond_wait (&prod->notfull, &prod->Lock);//waiting for a space to write    }    //Write DataProd->buffer[prod->writepos] =data; Prod->writepos++; if(Prod->writepos >=buffer_size) Prod->writepos =0; Pthread_cond_signal (&prod->notempty); Pthread_mutex_unlock (&prod->Lock);}//read a data from a bufferint Get(structProdcons *prod) {    intdata; //Lock MutexPthread_mutex_lock (&prod->Lock);  while(Prod->writepos = = prod->Readpos) {printf ("producer wait for not empty\n"); Pthread_cond_wait (&prod->notempty, &prod->Lock); } Data= prod->buffer[prod->Readpos]; Prod->readpos++; if(Prod->readpos >=buffer_size) Prod->readpos =0; Pthread_cond_signal (&prod->notfull); Pthread_mutex_unlock (&prod->Lock); returndata;}#defineOver (-1)structprodcons buffer;//producersvoid* Producer (void*data) {    intN;  for(n =1; N <=5; n++)//production of 5 products{printf ("producer Sleep 1 second...\n"); Sleep (1); printf ("put the%d product\n", N); Put (&buffer, n); }     for(n =6; N <=Ten; n++) {printf ("producer Sleep 3 second...\n"); Sleep (3); printf ("put the%d product\n", N); Put (&buffer, n); } put (&buffer, over); printf ("producer Stopped!\n"); returnNULL;}//Consumervoid* Consumer (void*data) {    intD =0;  while(1) {printf ("Consumer Sleep 2 second...\n"); Sleep (2); D=Get(&buffer); printf ("get the%d product\n", D); if(d = =Over ) Break; } printf ("Consumer stopped!\n"); returnNULL;}intMainintargcChar*argv[])    {pthread_t th_a, th_b; void*retval; Init (&buffer); Pthread_create (&th_a, NULL, producer,0); Pthread_create (&th_b, NULL, Consumer,0); Pthread_join (Th_a,&retval); Pthread_join (Th_b,&retval); return 0;}

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"Linux Advanced Programming" (12th) Linux multithreaded Programming 3