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);}