No and no. You simply need to be careful and set close-on-exec on all file descriptors you care about. Setting it is easy, though: #include <fcntl.h> fcntl(fd, F_SETFD, fcntl(fd, F_GETFD) | FD_CLOEXEC); #include <unistd.h> /* please don’t do this */ for (i = getdtablesize(); i –> 3;) { if ((flags = fcntl(i, F_GETFD)) != -1) … Read more
If you fork with the purpose of calling an exec function, you can use fcntl with FD_CLOEXEC to have the file descriptor closed once you exec: int fd = open(…); fcntl(fd, F_SETFD, FD_CLOEXEC); Such a file descriptor will survive a fork but not functions of the exec family.
The child process inherits signal handlers from the parent, but not the pending signal. After forking try installing the signal handler for SIGTRAP at a place in code where the child process executes after forking. If you don’t handle SIGTRAP, the default action is that the child is terminated. If you want to debug the … Read more
Then you want to use the waitpid function with the WNOHANG option: #include <sys/types.h> #include <sys/wait.h> int status; pid_t return_pid = waitpid(process_id, &status, WNOHANG); /* WNOHANG def’d in wait.h */ if (return_pid == -1) { /* error */ } else if (return_pid == 0) { /* child is still running */ } else if (return_pid … Read more
The output of your program is highly implementation dependent. The C standard library applies buffering to the output stream. This means that it accumulates characters to write until the buffer reaches a certain length (or until a certain condition is met), and then outputs all the text at once. The most common behavior is to … Read more
It might help to first understand why the word fork was used to name this function. Ever heard of a “fork on the road?” At a fork, the process has to split paths. First there is a single process executing normally until you reach the fork call. When fork is called, a new process is … Read more
PCNTL can not make threads. It only “forks” current PHP process. What does it mean? When you call pcntl_fork(), current process is split into two processes. Whole namespace of parent process is copied into the child and both processes continue with execution in parallel with only one difference: pcntl_fork() returns child’s PID in parent and … Read more
It looks to me as though the basic problem is that you have one wait() call rather than a loop that waits until there are no more children. You also only wait if the last fork() is successful rather than if at least one fork() is successful. You should only use _exit() if you don’t … Read more
Here’s how to understand it, starting at the for loop. Loop starts in parent, i == 0 Parent fork()s, creating child 1. You now have two processes. Both print i=0. Loop restarts in both processes, now i == 1. Parent and child 1 fork(), creating children 2 and 3. You now have four processes. All … Read more
The main difference between forking and threading approaches is one of operating system architecture. Back in the days when Unix was designed, forking was an easy, simple system that answered the mainframe and server type requirements best, as such it was popularized on the Unix systems. When Microsoft re-architected the NT kernel from scratch, it … Read more