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#include "apue.h"#include 
   
    #include 
    
     #include 
     
      extern int makethread(void *(*)(void *), void *);struct to_info{    void (*to_fn)(void *);    void *to_arg;    struct timespec to_wait;};#define SECTONSEC 100000000000#if !defined(CLOCK_REALTIME)||defined(BSD)#define clock_nanosleep(ID,FL,REQ,REM) nanosleep((REQ),(REM))#endif#ifndef CLOCK_REALTIME#define CLOCK_REALTIME 0#define USECTONSEC 1000void clock_gettime(int id, struct timespec *tsp){    struct timeval tv;        gettimeofday(&tv,NULL);    tsp->tv_sec=tv.tv_sec;    tsp->tv_nsec=tv.tv_usec*USECTONSEC;}#endifvoid *timeout_helper(void *arg){    struct to_info *tip;    tip=(struct to_info*)arg;    clock_nanosleep(CLOCK_REALTIME,0,&tip->to_wait,NULL);    (*tip->to_fn)(tip->to_arg);    free(arg);    return 0;}void timeout(const struct timespec *when, void (*func)(void *), void *arg){    struct timespec now;    struct to_info *tip;    int err;    clock_gettime(CLOCK_REALTIME,&now);    if((when->tv_sec>now.tv_sec)||        (when->tv_sec==now.tv_sec&&when->tv_nsec>now.tv_nsec))    {        tip=malloc(sizeof(struct to_info));        if(tip!=NULL)        {            tip->to_fn=func;            tip->to_arg=arg;            tip->to_wait.tv_sec=when->tv_sec-now.tv_sec;            if(when->tv_nsec>=now.tv_nsec)            {                tip->to_wait.tv_nsec=when->tv_nsec-now.tv_nsec;            }            else            {                tip->to_wait.tv_sec--;                tip->to_wait.tv_nsec=SECTONSEC-now.tv_nsec+when->tv_nsec;            }            err=makethread(timeout_helper,(void *)tip);            if(err==0)                return ;            else                free(tip);        }    }    (*func)(arg);}pthread_mutexattr_t attr;pthread_mutex_t mutex;void retry(void *arg){    pthread_mutex_lock(&mutex);    pthread_mutex_unlock(&mutex);}int main(void){    int err, condition, arg;    struct timespec when;    if((err=pthread_mutexattr_init(&attr))!=0)        err_exit(err,"pthread_mutexattr_init failed");    if((err=pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE))!=0)        err_exit(err, "can't set recursive type");        pthread_mutex_lock(&mutex);    if(condition)    {        clock_gettime(CLOCK_REALTIME, &when);        when.tv_sec+=10;        timeout(&when, retry, (void *)((unsigned long)arg));    }    pthread_mutex_unlock(&mutex);    return 0;}
     
    
   

Using a recursive mutex

We could call sleep to wait for the timeout to expire, but that gives us only second granularity. If we want to wait for some time other than an integral number of seconds, we need to use nanosleep or clock_nanosleep, both of which allow us to sleep at higher resolution.

On systems that don’t define CLOCK_REALTIME, we define clock_nanosleep in terms of nanosleep. However, FreeBSD 8.0 defines this symbol to support clock_gettime and clock_settime, but doesn’t support clock_nanosleep (only Linux 3.2.0 and Solaris 10 currently support clock_nanosleep.)

Additionally, on systems that don’t define CLOCK_REALTIME, we provide our own implementation of clock_gettime that calls gettimeofday and translates microseconds to nanoseconds.

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