POSIX 多线程编程及理解

pthread_create (thread,attr,start_routine,arg) 

pthread_exit (status)

pthread_cancel (thread)

pthread_attr_init (attr)

pthread_attr_destroy (attr) 

/******************************************************************************
* FILE: hello.c
* DESCRIPTION:
*   A "hello world" Pthreads program.  Demonstrates thread creation and
*   termination.
* AUTHOR: Blaise Barney
* LAST REVISED: 08/09/11
******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define NUM_THREADS    5

void *PrintHello(void *threadid)
{
   long tid;
   tid = (long)threadid;
   printf("Hello World! It‘s me, thread #%ld!\n", tid);
   pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
   pthread_t threads[NUM_THREADS];
   int rc;
   long t;
   for(t=0;t<NUM_THREADS;t++){
     printf("In main: creating thread %ld\n", t);
     rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
     if (rc){
       printf("ERROR; return code from pthread_create() is %d\n", rc);
       exit(-1);
       }
     }

   /* Last thing that main() should do */
   pthread_exit(NULL);
}

 #include <pthread.h>
 #include <stdio.h>
 #include <stdlib.h>

 /*   
 The following structure contains the necessary information  
 to allow the function "dotprod" to access its input data and 
 place its output into the structure.  
 */

 typedef struct 
  {
    double      *a;
    double      *b;
    double     sum; 
    int     veclen; 
  } DOTDATA;

 /* Define globally accessible variables and a mutex */

 #define NUMTHRDS 4
 #define VECLEN 100
    DOTDATA dotstr; 
    pthread_t callThd[NUMTHRDS];
    pthread_mutex_t mutexsum;

 /*
 The function dotprod is activated when the thread is created.
 All input to this routine is obtained from a structure 
 of type DOTDATA and all output from this function is written into
 this structure. The benefit of this approach is apparent for the 
 multi-threaded program: when a thread is created we pass a single
 argument to the activated function - typically this argument
 is a thread number. All  the other information required by the 
 function is accessed from the globally accessible structure. 
 */  

 void *dotprod(void *arg)
 {

    /* Define and use local variables for convenience */

    int i, start, end, len ;
    long offset;
    double mysum, *x, *y;
    offset = (long)arg;
     
    len = dotstr.veclen;
    start = offset*len;
    end   = start + len;
    x = dotstr.a;
    y = dotstr.b;

    /*
    Perform the dot product and assign result
    to the appropriate variable in the structure. 
    */

    mysum = 0;
    for (i=start; i<end ; i++) 
     {
       mysum += (x[i] * y[i]);
     }

    /*
    Lock a mutex prior to updating the value in the shared
    structure, and unlock it upon updating.
    */
    pthread_mutex_lock (&mutexsum);
    dotstr.sum += mysum;
    pthread_mutex_unlock (&mutexsum);

    pthread_exit((void*) 0);
 }

 /* 
 The main program creates threads which do all the work and then 
 print out result upon completion. Before creating the threads,
 the input data is created. Since all threads update a shared structure, 
 we need a mutex for mutual exclusion. The main thread needs to wait for
 all threads to complete, it waits for each one of the threads. We specify
 a thread attribute value that allow the main thread to join with the
 threads it creates. Note also that we free up handles when they are
 no longer needed.
 */

 int main (int argc, char *argv[])
 {
    long i;
    double *a, *b;
    void *status;
    pthread_attr_t attr;  

    /* Assign storage and initialize values */
    a = (double*) malloc (NUMTHRDS*VECLEN*sizeof(double));
    b = (double*) malloc (NUMTHRDS*VECLEN*sizeof(double));
   
    for (i=0; i<VECLEN*NUMTHRDS; i++)
      {
      a[i]=1.0;
      b[i]=a[i];
      }

    dotstr.veclen = VECLEN; 
    dotstr.a = a; 
    dotstr.b = b; 
    dotstr.sum=0;

    pthread_mutex_init(&mutexsum, NULL);
         
    /* Create threads to perform the dotproduct  */
    pthread_attr_init(&attr);
    pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

    for(i=0; i<NUMTHRDS; i++)
    {
    /* 
    Each thread works on a different set of data. The offset is specified 
    by ‘i‘. The size of the data for each thread is indicated by VECLEN.
    */
    pthread_create(&callThd[i], &attr, dotprod, (void *)i);
    }

    pthread_attr_destroy(&attr);

    /* Wait on the other threads */
    for(i=0; i<NUMTHRDS; i++)
       {
       pthread_join(callThd[i], &status);
       }

    /* After joining, print out the results and cleanup */
    printf ("Sum =  %f \n", dotstr.sum);
    free (a);
    free (b);
    pthread_mutex_destroy(&mutexsum);
    pthread_exit(NULL);
 }   

/******************************************************************************
* FILE: condvar.c
* DESCRIPTION:
*   Example code for using Pthreads condition variables.  The main thread
*   creates three threads.  Two of those threads increment a "count" variable,
*   while the third thread watches the value of "count".  When "count" 
*   reaches a predefined limit, the waiting thread is signaled by one of the
*   incrementing threads. The waiting thread "awakens" and then modifies
*   count. The program continues until the incrementing threads reach
*   TCOUNT. The main program prints the final value of count.
* SOURCE: Adapted from example code in "Pthreads Programming", B. Nichols
*   et al. O‘Reilly and Associates. 
* LAST REVISED: 03/07/17  Blaise Barney
******************************************************************************/
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

#define NUM_THREADS  3
#define TCOUNT 10
#define COUNT_LIMIT 12

int     count = 0;
pthread_mutex_t count_mutex;
pthread_cond_t count_threshold_cv;

void *inc_count(void *t) 
{
  int i;
  long my_id = (long)t;

  for (i=0; i < TCOUNT; i++) {
    pthread_mutex_lock(&count_mutex);
    count++;

    /* 
    Check the value of count and signal waiting thread when condition is
    reached.  Note that this occurs while mutex is locked. 
    */
    if (count == COUNT_LIMIT) {
      printf("inc_count(): thread %ld, count = %d  Threshold reached. ",
             my_id, count);
      pthread_cond_signal(&count_threshold_cv);
      printf("Just sent signal.\n");
      }
    printf("inc_count(): thread %ld, count = %d, unlocking mutex\n", 
       my_id, count);
    pthread_mutex_unlock(&count_mutex);

    /* Do some work so threads can alternate on mutex lock */
    sleep(1);
    }
  pthread_exit(NULL);
}

void *watch_count(void *t) 
{
  long my_id = (long)t;

  printf("Starting watch_count(): thread %ld\n", my_id);

  /*
  Lock mutex and wait for signal.  Note that the pthread_cond_wait routine
  will automatically and atomically unlock mutex while it waits. 
  Also, note that if COUNT_LIMIT is reached before this routine is run by
  the waiting thread, the loop will be skipped to prevent pthread_cond_wait
  from never returning.
  */
  pthread_mutex_lock(&count_mutex);
  while (count < COUNT_LIMIT) {
    printf("watch_count(): thread %ld Count= %d. Going into wait...\n", my_id,count);
    pthread_cond_wait(&count_threshold_cv, &count_mutex);
    printf("watch_count(): thread %ld Condition signal received. Count= %d\n", my_id,count);
    }
  printf("watch_count(): thread %ld Updating the value of count...\n", my_id);
  count += 125;
  printf("watch_count(): thread %ld count now = %d.\n", my_id, count);
  printf("watch_count(): thread %ld Unlocking mutex.\n", my_id);
  pthread_mutex_unlock(&count_mutex);
  pthread_exit(NULL);
}

int main(int argc, char *argv[])
{
  int i, rc; 
  long t1=1, t2=2, t3=3;
  pthread_t threads[3];
  pthread_attr_t attr;

  /* Initialize mutex and condition variable objects */
  pthread_mutex_init(&count_mutex, NULL);
  pthread_cond_init (&count_threshold_cv, NULL);

  /* For portability, explicitly create threads in a joinable state */
  pthread_attr_init(&attr);
  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);
  pthread_create(&threads[0], &attr, watch_count, (void *)t1);
  pthread_create(&threads[1], &attr, inc_count, (void *)t2);
  pthread_create(&threads[2], &attr, inc_count, (void *)t3);

  /* Wait for all threads to complete */
  for (i = 0; i < NUM_THREADS; i++) {
    pthread_join(threads[i], NULL);
  }
  printf ("Main(): Waited and joined with %d threads. Final value of count = %d. Done.\n", 
          NUM_THREADS, count);

  /* Clean up and exit */
  pthread_attr_destroy(&attr);
  pthread_mutex_destroy(&count_mutex);
  pthread_cond_destroy(&count_threshold_cv);
  pthread_exit (NULL);

}