開源鴻蒙Fork和Waitpid測試

前言

最近做項目需要用到多進程部分河劝，并在不同平臺進行測試渔欢，現(xiàn)將結(jié)果記錄如下：

接口介紹

• fork

  #include <unistd.h>
  //creates a new process by duplicating the calling process.
  //The new process is referred to as the child process.  The calling
  //process is referred to as the parent process.
  //The child process and the parent process run in separate memory
  //spaces.  At the time of fork() both memory spaces have the same
  //content.  Memory writes, file mappings (mmap(2)), and unmappings
  //(munmap(2)) performed by one of the processes do not affect the
  //other.
  //Return
  //On success, the PID of the child process is returned in the
  //parent, and 0 is returned in the child.  On failure, -1 is
  //returned in the parent, no child process is created, and errno is
  //set to indicate the error.
  
  pid_t fork(void);
  

• wait

  #include <sys/types.h>
  #include <sys/wait.h>
  //The wait() system call suspends execution of the calling thread
  //until one of its children terminates.  The call wait(&wstatus) is
  //equivalent to:waitpid(-1, &wstatus, 0);
  //Return
  //on success, returns the process ID of the terminated
  //child; on failure, -1 is returned.
  
  pid_t wait(int *status);
  

• waitpid

  #include <sys/types.h>
  #include <sys/wait.h>
  //The waitpid() system call suspends execution of the calling
  //thread until a child specified by pid argument has changed state.
  //By default, waitpid() waits only for terminated children, but
  //this behavior is modifiable via the options argument, as
  //described below.
  //The value of pid can be:
  //  < -1   meaning wait for any child process whose process group ID
  //         is equal to the absolute value of pid.
  //  -1     meaning wait for any child process.
  //  0      meaning wait for any child process whose process group ID
  //         is equal to that of the calling process at the time of the
  //         call to waitpid().
  //  > 0    meaning wait for the child whose process ID is equal to
  //         the value of pid.
  //The value of options is an OR of zero or more of the following
  //constants:
  //  WNOHANG
  //    return immediately if no child has exited.
  //  WUNTRACED
  //    also return if a child has stopped (but not traced via
  //    ptrace(2)).  Status for traced children which have stopped
  //    is provided even if this option is not specified.
  //  WCONTINUED (since Linux 2.6.10)
  //    also return if a stopped child has been resumed by
  //    delivery of SIGCONT.
  //Return
  //on success, returns the process ID of the child whose
  //state has changed; if WNOHANG was specified and one or more
  //child(ren) specified by pid exist, but have not yet changed
  //state, then 0 is returned.  On failure, -1 is returned.
  
  pid_t waitpid(pid_t pid, int *status, int options);
  

  測試代碼1

  以下代碼設(shè)計為啟動兩個進程雹姊，然后在主進程等待執(zhí)行完成初橘，查看返回值后執(zhí)行主進程

  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <sys/types.h>
  #include <sys/wait.h>
  
  int main()
  {
    pid_t child1, child2;
    pid_t rc1, rc2;
    printf("parent(pid = %d, ppid = %d\n", getpid(), getppid());
    if ((child1 = fork()) == 0)
    {
      for (int i = 1; i <= 10; i++)
      {
        printf("child1(process=%d%) is working!(pid=%d,ppid=%d)\n", i * 10, getpid(), getppid());
        sleep(1);
      }
      printf("child1 had completed!\n");
    }
    else if (child1 > 0)
    {
      if ((child2 = fork()) == 0)
      {
        for (int i = 1; i <= 10; i++)
        {
          printf("child2(process=%d%) is working!(pid=%d,ppid=%d)\n", i * 10, getpid(), getppid());
          sleep(1);
        }
        printf("child2 had completed!\n");
      }
      else if (child2 > 0)
      {
        //option = 0意味著阻塞父進程等子進程結(jié)束
        rc1 = waitpid(child1, NULL, 0);
        rc2 = waitpid(child2, NULL, 0);
        printf("rc1=%d, rc2=%d\n", rc1, rc2);
        printf("child1=%d, child2=%d\n", child1, child2);
  
        for (int i = 1; i <= 3; i++)
        {
          printf("parent(process=%d%) is working!(pid=%d,ppid=%d)\n", i * 10, getpid(), getppid());
          sleep(1);
        }
        printf("parent had completed!\n");
      }
      else if (child2 == -1)
      {
        printf("Error!\n");
      }
    }
    else
    {
      printf("Error!\n");
    }
    return 0;
  }
  

  測試結(jié)果1

  • Linux

    
    
    Linux測試

  • OHOS（開源鴻蒙開發(fā)板，RK3568）

    
    
    OHOS測試

  總結(jié)1

  Linux下可按照設(shè)計目標執(zhí)行幢炸，但是OHOS下waitpid返回值為-1泄隔，意味沒有找到子進程；但是實際上waitpid是找到子進程并等待子進程執(zhí)行完畢后才執(zhí)行的主進程宛徊。

  測試代碼2

  以下代碼設(shè)計為啟動兩個進程佛嬉，然后在主進程等待執(zhí)行完成，查看返回值后執(zhí)行主進程

  #include <stdio.h>
  #include <stdlib.h>
  #include <unistd.h>
  #include <sys/types.h>
  #include <sys/wait.h>
  
  int main()
  {
    pid_t child1, child2;
    pid_t rc1, rc2;
    printf("parent(pid = %d, ppid = %d\n", getpid(), getppid());
    if ((child1 = fork()) == 0)
    {
      for (int i = 1; i <= 10; i++)
      {
        printf("child1(process=%d%) is working!(pid=%d,ppid=%d)\n", i * 10, getpid(), getppid());
        sleep(1);
      }
      printf("child1 had completed!\n");
    }
    else if (child1 > 0)
    {
      if ((child2 = fork()) == 0)
      {
        for (int i = 1; i <= 10; i++)
        {
          printf("child2(process=%d%) is working!(pid=%d,ppid=%d)\n", i * 10, getpid(), getppid());
          sleep(1);
        }
        printf("child2 had completed!\n");
      }
      else if (child2 > 0)
      {
        //option = WNOHANG 意味著不阻塞父進程闸天，子進程和父進程交替運行
        rc1 = waitpid(child1, NULL, WNOHANG);
        rc2 = waitpid(child2, NULL, WNOHANG);
        printf("rc1=%d, rc2=%d\n", rc1, rc2);
        printf("child1=%d, child2=%d\n", child1, child2);
  
        for (int i = 1; i <= 3; i++)
        {
          printf("parent(process=%d%) is working!(pid=%d,ppid=%d)\n", i * 10, getpid(), getppid());
          sleep(1);
        }
        printf("parent had completed!\n");
      }
      else if (child2 == -1)
      {
        printf("Error!\n");
      }
    }
    else
    {
      printf("Error!\n");
    }
    return 0;
  }
  

  測試結(jié)果2

  • Linux

    
    
    Linux測試

  • OHOS

    
    
    OHOS測試

總結(jié)2

WNOHANG：意味不阻塞進程立即返回暖呕，如果子進程存在但是沒有狀態(tài)變化則返回0；Linux執(zhí)行可看出進程是交替執(zhí)行的苞氮，但是OHOS子進程好像沒有搶到執(zhí)行權(quán)限湾揽，所以只有等父進程執(zhí)行完畢后才依次執(zhí)行子進程。