CODEWITHSUNDEEP
c++linuxsystem-calls
user2212461
user2212461

Reputation: 3253

How to stop Linux "read" system call from blocking?

How can a read Linux system call be unblocked in C++? If I have for example in a thread the following loop :

bool shouldRun;

void foo(){
  while(shouldRun){
    length = read( file_descriptor, buffer, buffer_length);
    //do something
  }
  return;
}

main(){
  shouldRun = true;
  std::thread myThread(foo);
  //do some other stuff
  shouldRun = false;
  //-->here I want to unblock "read" in foo
}

Generally the read method should block, I only want to unblock it when needed.

Upvotes: 2

Views: 6368

Answers (3)

Moonsurfer_1
Moonsurfer_1

Reputation: 115

I'm going to assume that the read call is waiting for data to become available and it's blocking because of this.

That's why I'd suggest you check if data is available before reading:

    #include <sys/ioctl.h>

    ...

    int count;
    ioctl(file_descriptor, FIONREAD, &count);

Upvotes: 0

Non-maskable Interrupt
Non-maskable Interrupt

Reputation: 3911

the libc read() function internally invoke syscall in kernel side. The (linux) kernel region is generally not support abort due to its design (yes this can make process non-killable in some case)

To archive your goal, you should make read() non-blocking so that the kernel call return immediately, or check if data ready before read() using select().

Upvotes: 0

doron
doron

Reputation: 28892

call

fcntl(fd, F_SETFL, flags | O_NONBLOCK);

This will make the file descriptor non-blocking.

Upvotes: 3

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