C waitpid(pid、状态、选项)不总是设置状态
我正在为一项任务复制shell管道。我让管道全部正常工作(此后没有更改管道代码,因此这是已知的正常工作),但仍然需要在管道的某个步骤执行失败时终止管道。在实现该代码的某个时刻,管道开始表现出意外的行为 长度为2的管道工作正常。 长度大于两条的管道以以下方式失效:C waitpid(pid、状态、选项)不总是设置状态,c,system-calls,waitpid,C,System Calls,Waitpid,我正在为一项任务复制shell管道。我让管道全部正常工作(此后没有更改管道代码,因此这是已知的正常工作),但仍然需要在管道的某个步骤执行失败时终止管道。在实现该代码的某个时刻,管道开始表现出意外的行为 长度为2的管道工作正常。 长度大于两条的管道以以下方式失效: 执行管道中的第一个命令 紧接着-通常在第一个命令完成执行之前-管道中的最后一个命令终止 第二个命令将挂起,显然没有收到第一个命令的输入 以下是使用waitpid(sans调试代码)的部分代码: 要从waitpid()返回的值提取通过进程
要从
waitpid()
返回的值提取通过进程传递给exit()
的状态,请使用宏WEXITSTATUS()
此外,waitpid()
的故障测试也是错误的waitpid()失败时返回-1,在本例中设置为
errno,然后通过调用
perror()来解释它
perror()
读取errno
的值。因此,只有当已知已设置了errno
时,调用peror()
才有意义。调用perror(“Error”)
I remove in my modification of your code时,情况并非如此,如下所示
for (int i = 0 ; i < num_cmds ; i++)
{
int status = -1;
int result = waitpid(cmd_pids[i], &status, NULL);
if (-1 == result)
{
perror("waitpid()"); /* added call to perror() here as errno is know to have been set */
}
else
{
if (result != cmd_pids[i])
{
fprintf(stderr, "Error waiting for command '%s'\n", cmds[i]);
/* removed call to perror() here as errno had not been set here. As this however should
log an error, I modded the code to printf to stderr, but stdout. */
}
else
{
cmd_status[i] = WEXITSTATUS(status);
if ((cmd_status[i] > 0) && ((0 == i) || (cmd_status[i-1] == 0))) /* This mod keeps
the app from dereferencing cmd_status in case i == 0, as this would lead to
cmd_status[-1], which is undefined beaviour. */
{
killPipeline(SIGINT); //Kill pipeline; something failed
}
}
}
...
for(int i=0;i0)和((0==i)| |(cmd_状态[i-1]==0))/*此模块保持
在i==0的情况下,应用程序不会取消对cmd_状态的引用,因为这将导致
cmd_状态[-1],它是未定义的beaviour*/
{
killPipeline(SIGINT);//Kill pipeline;某些操作失败
}
}
}
...
向所有试图发现waitpid问题的人致歉,因为这些问题只是表面错误。实际错误确实存在于我的管道代码中,我显然在过程中破坏了管道代码。我认为在您的第二个if语句中,cmd_status[I-1]!=0,因为0表示这些进程尚未完成(更改状态).虽然我看到这里有很多小问题,我很感激你指出了这些问题,但这些变化都没有(我已经实施了)实际上解决了这个奇怪的行为。实际上,我试图从上一次提交开始,并重新实现管道更改以重新启动。同样的行为,因此我无法再保证管道代码是正确的。
You entered : list of pipe commands ls | grep pipe | wc
Creating process ls
Creating process grep pipe
Creating process wc
Waiting for command ls
0 0 0 //wc received no input, but somehow an EOF
Command ls finished
Waiting for command grep
^C //Terminate grep because it's waiting for input from a terminated process
Error waiting for command grep
Error: Interrupted system call
Command grep finished
Waiting for command wc
Command wc finished
for (int i = 0 ; i < num_cmds ; i++)
{
int status = -1;
int result = waitpid(cmd_pids[i], &status, NULL);
if (-1 == result)
{
perror("waitpid()"); /* added call to perror() here as errno is know to have been set */
}
else
{
if (result != cmd_pids[i])
{
fprintf(stderr, "Error waiting for command '%s'\n", cmds[i]);
/* removed call to perror() here as errno had not been set here. As this however should
log an error, I modded the code to printf to stderr, but stdout. */
}
else
{
cmd_status[i] = WEXITSTATUS(status);
if ((cmd_status[i] > 0) && ((0 == i) || (cmd_status[i-1] == 0))) /* This mod keeps
the app from dereferencing cmd_status in case i == 0, as this would lead to
cmd_status[-1], which is undefined beaviour. */
{
killPipeline(SIGINT); //Kill pipeline; something failed
}
}
}
...