POSIX 计时器在运行几次后挂断

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POSIX timer hangs up after a few runs

我在程序的主函数中创建了一个 POSIX 计时器。主程序的每个线程都在设置计时器，以便在它到期时，信号处理程序更新一个变量，该变量唤醒同一进程的下一个线程。

计时器大部分时间都可以正常工作，但并非总是如此。它有时会完成完整的执行，而在其他运行中，它会挂起。可能的原因是什么？我的怀疑与信号传递有关。

代码如下：

#define _GNU_SOURCE

#define _POSIX_C_SOURCE 199309

#include <sched.h>

#include <unistd.h>

#include <sys/wait.h>

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

#include <unistd.h>

#include <signal.h>

#include <errno.h>

#include <semaphore.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <syscall.h>

#define NUM_THREADS 10



#define CLOCKID CLOCK_REALTIME

#define SIG SIGUSR1

int ret;

timer_t timerid;

struct sigevent sev;

struct itimerspec its;

long long freq_nanosecs;

sigset_t mask;

struct sigaction sa;



sem_t sem[NUM_THREADS];

sem_t mute;



pthread_t tid[NUM_THREADS];

int state = 0;



static void handler(int sig, siginfo_t *si, void *uc)

{

  ret = sem_post(&sem[(state+1)%NUM_THREADS]);

    if (ret)

    {

      printf("Error in Sem Post\

");

    }

    state++;

}



void *threadA(void *data_)

{ 

  int i = 0, s,n,value;



  long int loopNum;

  int turn = (intptr_t)data_;

  struct timespec tval_result,tval_result2;



  int sid = syscall(SYS_gettid);

  FILE *fp;

  fp=fopen("ipc.out","a");  

  fprintf(fp,"thread_%d %d\

",turn,sid); 

  fclose(fp); 



  int counter=0;



  while(1)

  {

    ret = sem_wait(&sem[turn]);

    if (ret)

    {

      printf("Error in Sem Post\

");

    }

    //printf("Thread # -> %d\

",turn);



    its.it_value.tv_sec = 0;

    its.it_value.tv_nsec = 14000;

    its.it_interval.tv_sec = 0;

    its.it_interval.tv_nsec = 0;



    ret = timer_settime(timerid, 0, &its, NULL);

    if ( ret < 0 )

      perror("timer_settime");



    // Some heavy work



  counter++;



  if(counter==100)

  break;

  }

  printf("finished %d\

",turn);



}



int main(int argc, char *argv[])

{

  int data = 0;

  int err,i;



  sa.sa_flags = SA_RESTART;

  sa.sa_sigaction = handler;

  sigemptyset(&sa.sa_mask);

  sigaction(SIG, &sa, NULL);



  sev.sigev_notify = SIGEV_SIGNAL;

  sev.sigev_signo = SIG;

  sev.sigev_value.sival_ptr = &timerid;

  ret = timer_create(CLOCKID, &sev, &timerid);

  if ( ret < 0 )

    perror("timer_create");



  sem_init(&sem[0], 0, 1); 

  for ( i = 1; i < NUM_THREADS; ++i)

    {

      sem_init(&sem[i], 0, 0); 

    }



  while(data < NUM_THREADS)

  {

    //create our threads

    err = pthread_create(&tid[data], NULL, threadA, (void *)(intptr_t)data);

    if(err != 0)

      printf("\

can't create thread :[%s]", strerror(err));



    data++;

  }



  pthread_exit(NULL);

}
finished 0

finished 1

finished 2

finished 3

finished 4

finished 5

finished 6

finished 7

finished 8

finished 9

static void handler(int sig, siginfo_t *si, void *uc)

{

  state++;

  ret = sem_post(&sem[(state)%NUM_THREADS]);

  if (ret)

  {

    printf("Error in Sem Post\

");

  }

}

据此，这个程序应该打印

#define _GNU_SOURCE

#define _POSIX_C_SOURCE 199309

#include <sched.h>

#include <unistd.h>

#include <sys/wait.h>

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

#include <unistd.h>

#include <signal.h>

#include <errno.h>

#include <semaphore.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <syscall.h>

#define NUM_THREADS 10



#define CLOCKID CLOCK_REALTIME

#define SIG SIGUSR1

int ret;

timer_t timerid;

struct sigevent sev;

struct itimerspec its;

long long freq_nanosecs;

sigset_t mask;

struct sigaction sa;



sem_t sem[NUM_THREADS];

sem_t mute;



pthread_t tid[NUM_THREADS];

int state = 0;



static void handler(int sig, siginfo_t *si, void *uc)

{

  ret = sem_post(&sem[(state+1)%NUM_THREADS]);

    if (ret)

    {

      printf("Error in Sem Post\

");

    }

    state++;

}



void *threadA(void *data_)

{ 

  int i = 0, s,n,value;



  long int loopNum;

  int turn = (intptr_t)data_;

  struct timespec tval_result,tval_result2;



  int sid = syscall(SYS_gettid);

  FILE *fp;

  fp=fopen("ipc.out","a");  

  fprintf(fp,"thread_%d %d\

",turn,sid); 

  fclose(fp); 



  int counter=0;



  while(1)

  {

    ret = sem_wait(&sem[turn]);

    if (ret)

    {

      printf("Error in Sem Post\

");

    }

    //printf("Thread # -> %d\

",turn);



    its.it_value.tv_sec = 0;

    its.it_value.tv_nsec = 14000;

    its.it_interval.tv_sec = 0;

    its.it_interval.tv_nsec = 0;



    ret = timer_settime(timerid, 0, &its, NULL);

    if ( ret < 0 )

      perror("timer_settime");



    // Some heavy work



  counter++;



  if(counter==100)

  break;

  }

  printf("finished %d\

",turn);



}



int main(int argc, char *argv[])

{

  int data = 0;

  int err,i;



  sa.sa_flags = SA_RESTART;

  sa.sa_sigaction = handler;

  sigemptyset(&sa.sa_mask);

  sigaction(SIG, &sa, NULL);



  sev.sigev_notify = SIGEV_SIGNAL;

  sev.sigev_signo = SIG;

  sev.sigev_value.sival_ptr = &timerid;

  ret = timer_create(CLOCKID, &sev, &timerid);

  if ( ret < 0 )

    perror("timer_create");



  sem_init(&sem[0], 0, 1); 

  for ( i = 1; i < NUM_THREADS; ++i)

    {

      sem_init(&sem[i], 0, 0); 

    }



  while(data < NUM_THREADS)

  {

    //create our threads

    err = pthread_create(&tid[data], NULL, threadA, (void *)(intptr_t)data);

    if(err != 0)

      printf("\

can't create thread :[%s]", strerror(err));



    data++;

  }



  pthread_exit(NULL);

}
finished 0

finished 1

finished 2

finished 3

finished 4

finished 5

finished 6

finished 7

finished 8

finished 9

static void handler(int sig, siginfo_t *si, void *uc)

{

  state++;

  ret = sem_post(&sem[(state)%NUM_THREADS]);

  if (ret)

  {

    printf("Error in Sem Post\

");

  }

}

有时会这样打印，但大多数时候，程序会挂起。

信号处理程序有一个竞争条件。一旦 sem_post 被调用，其他线程之一就可以开始运行，并且它的计时器可以在当前信号处理程序完成之前触发。这将导致在另一个线程中再次调用信号处理程序。此时 state 没有被第一个线程递增，因此第二个信号处理程序调用最终会在错误的信号量上调用 sem_post。

解决此问题的一种方法是确保在调用 sem_post:

之前增加 state

#define _GNU_SOURCE

#define _POSIX_C_SOURCE 199309

#include <sched.h>

#include <unistd.h>

#include <sys/wait.h>

#include <stdio.h>

#include <stdlib.h>

#include <pthread.h>

#include <unistd.h>

#include <signal.h>

#include <errno.h>

#include <semaphore.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <syscall.h>

#define NUM_THREADS 10



#define CLOCKID CLOCK_REALTIME

#define SIG SIGUSR1

int ret;

timer_t timerid;

struct sigevent sev;

struct itimerspec its;

long long freq_nanosecs;

sigset_t mask;

struct sigaction sa;



sem_t sem[NUM_THREADS];

sem_t mute;



pthread_t tid[NUM_THREADS];

int state = 0;



static void handler(int sig, siginfo_t *si, void *uc)

{

  ret = sem_post(&sem[(state+1)%NUM_THREADS]);

    if (ret)

    {

      printf("Error in Sem Post\

");

    }

    state++;

}



void *threadA(void *data_)

{ 

  int i = 0, s,n,value;



  long int loopNum;

  int turn = (intptr_t)data_;

  struct timespec tval_result,tval_result2;



  int sid = syscall(SYS_gettid);

  FILE *fp;

  fp=fopen("ipc.out","a");  

  fprintf(fp,"thread_%d %d\

",turn,sid); 

  fclose(fp); 



  int counter=0;



  while(1)

  {

    ret = sem_wait(&sem[turn]);

    if (ret)

    {

      printf("Error in Sem Post\

");

    }

    //printf("Thread # -> %d\

",turn);



    its.it_value.tv_sec = 0;

    its.it_value.tv_nsec = 14000;

    its.it_interval.tv_sec = 0;

    its.it_interval.tv_nsec = 0;



    ret = timer_settime(timerid, 0, &its, NULL);

    if ( ret < 0 )

      perror("timer_settime");



    // Some heavy work



  counter++;



  if(counter==100)

  break;

  }

  printf("finished %d\

",turn);



}



int main(int argc, char *argv[])

{

  int data = 0;

  int err,i;



  sa.sa_flags = SA_RESTART;

  sa.sa_sigaction = handler;

  sigemptyset(&sa.sa_mask);

  sigaction(SIG, &sa, NULL);



  sev.sigev_notify = SIGEV_SIGNAL;

  sev.sigev_signo = SIG;

  sev.sigev_value.sival_ptr = &timerid;

  ret = timer_create(CLOCKID, &sev, &timerid);

  if ( ret < 0 )

    perror("timer_create");



  sem_init(&sem[0], 0, 1); 

  for ( i = 1; i < NUM_THREADS; ++i)

    {

      sem_init(&sem[i], 0, 0); 

    }



  while(data < NUM_THREADS)

  {

    //create our threads

    err = pthread_create(&tid[data], NULL, threadA, (void *)(intptr_t)data);

    if(err != 0)

      printf("\

can't create thread :[%s]", strerror(err));



    data++;

  }



  pthread_exit(NULL);

}
finished 0

finished 1

finished 2

finished 3

finished 4

finished 5

finished 6

finished 7

finished 8

finished 9

static void handler(int sig, siginfo_t *si, void *uc)

{

  state++;

  ret = sem_post(&sem[(state)%NUM_THREADS]);

  if (ret)

  {

    printf("Error in Sem Post\

");

  }

}

请注意，此解决方案仍然存在一个问题。它不能确保 printf 调用的顺序正确。

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