线程私有数据

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

static pthread_key_t str_key;

static pthread_once_t str_alloc_key_once=PTHREAD_ONCE_INIT;
static void str_alloc_key();
static void str_alloc_destroy_accu(void* accu);

char* str_accumulate(const char* s)
{    char* accu;

pthread_once(&str_alloc_key_once,str_alloc_key);
accu=(char*)pthread_getspecific(str_key);
if(accu==NULL)
{    accu=malloc(1024);
if(accu==NULL)    return NULL;
accu[0]=0;

pthread_setspecific(str_key,(void*)accu);
printf("Thread %lx: allocating buffer at %p\n",pthread_self(),accu);
}
strcat(accu,s);
return accu;
}

static void str_alloc_key()
{
pthread_key_create(&str_key,str_alloc_destroy_accu);
printf("Thread %lx: allocated key %d\n",pthread_self(),str_key);
}

static void str_alloc_destroy_accu(void* accu)
{    printf("Thread %lx: freeing buffer at %p\n",pthread_self(),accu);
free(accu);
}

void* process(void *arg)
{    char* res;
res=str_accumulate("Resule of ");
if(strcmp((char*)arg,"first")==0)
sleep(3);
res=str_accumulate((char*)arg);
res=str_accumulate(" thread");
printf("Thread %lx: \"%s\"\n",pthread_self(),res);
return NULL;
}

int main(int argc,char* argv[])
{    char* res;
pthread_t th1,th2;
res=str_accumulate("Result of ");
pthread_create(&th1,NULL,process,(void*)"first");
pthread_create(&th2,NULL,process,(void*)"second");
res=str_accumulate("initial thread");
printf("Thread %lx: \"%s\"\n",pthread_self(),res);
pthread_join(th1,NULL);
pthread_join(th2,NULL);
pthread_exit(0);
}