While loop within thread is causing program to block (C)

-2

The point of threads is to be able to run multiple blocks of code at once. The first thing I think of when this possibility comes into my head is having two infinite loops running at once. Before I tried to get this working with two threads, I tried to get it to work with one, with no success.

So I have a thread like this:

void *myThread(void *args) {

    sleep(0.1);

    while (1) {



    }

    return NULL;

}

And I am creating the thread like so:

pthread_t thread_id;

printf("Before Threadn");

pthread_create(&thread_id, NULL, myThread, args);

pthread_join(thread_id, NULL);

printf("After Threadn");

When I run this, "After Thread" does not print! Why is this happening? This makes no sense to me.

asked Nov 21 '18 at 21:25

Matt X

1098

you might want to look up asynchronous functions

– Brian
Nov 21 '18 at 21:27

@Brian no. i dont want an async func here

– Matt X
Nov 21 '18 at 21:28

add a comment |

-2

So I have a thread like this:

void *myThread(void *args) {

    sleep(0.1);

    while (1) {



    }

    return NULL;

}

And I am creating the thread like so:

pthread_t thread_id;

printf("Before Threadn");

pthread_create(&thread_id, NULL, myThread, args);

pthread_join(thread_id, NULL);

printf("After Threadn");

When I run this, "After Thread" does not print! Why is this happening? This makes no sense to me.

asked Nov 21 '18 at 21:25

Matt X

1098

you might want to look up asynchronous functions

– Brian
Nov 21 '18 at 21:27

@Brian no. i dont want an async func here

– Matt X
Nov 21 '18 at 21:28

add a comment |

-2

So I have a thread like this:

void *myThread(void *args) {

    sleep(0.1);

    while (1) {



    }

    return NULL;

}

And I am creating the thread like so:

pthread_t thread_id;

printf("Before Threadn");

pthread_create(&thread_id, NULL, myThread, args);

pthread_join(thread_id, NULL);

printf("After Threadn");

When I run this, "After Thread" does not print! Why is this happening? This makes no sense to me.

asked Nov 21 '18 at 21:25

Matt X

1098

So I have a thread like this:

void *myThread(void *args) {

    sleep(0.1);

    while (1) {



    }

    return NULL;

}

And I am creating the thread like so:

pthread_t thread_id;

printf("Before Threadn");

pthread_create(&thread_id, NULL, myThread, args);

pthread_join(thread_id, NULL);

printf("After Threadn");

When I run this, "After Thread" does not print! Why is this happening? This makes no sense to me.

c multithreading

asked Nov 21 '18 at 21:25

Matt X

1098

asked Nov 21 '18 at 21:25

Matt X

1098

asked Nov 21 '18 at 21:25

Matt X

1098

asked Nov 21 '18 at 21:25

Matt X

1098

asked Nov 21 '18 at 21:25

Matt X

1098

you might want to look up asynchronous functions

– Brian
Nov 21 '18 at 21:27

@Brian no. i dont want an async func here

– Matt X
Nov 21 '18 at 21:28

add a comment |

you might want to look up asynchronous functions

– Brian
Nov 21 '18 at 21:27

@Brian no. i dont want an async func here

– Matt X
Nov 21 '18 at 21:28

you might want to look up asynchronous functions

– Brian
Nov 21 '18 at 21:27

@Brian no. i dont want an async func here

– Matt X
Nov 21 '18 at 21:28

add a comment |

1 Answer
1

active

oldest

votes

Because pthread_join(thread_id, NULL); waits for the thread to finish. And a thread running a while (1) {} loop will never finish.

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

do I need the pthread_join(thread_id, NULL); line then? @MartinHeralecký

– Matt X
Nov 21 '18 at 21:29

@MattX If you don't put it there, the After Thread message will print immediately after starting the thread, which will keep running.

– Martin Heralecký
Nov 21 '18 at 21:31

If you changed the code in myThread to loop 10 times and print something out or sleep and then return, you'd wait for it to finish with the call to pthread_join in main. And after that your program could exit. If you just leave myThread as it is and take out the call to pthread_join, your program won't wait for the thread to finish and exit right away.

– bruceg
Nov 21 '18 at 21:36

@MattX Whether or not you need it depends on exactly what you're trying to do, which we do not know. What you should do depends on exactly what this thread is doing and how it relates to what the program as a whole is doing.

– David Schwartz
Nov 21 '18 at 21:39

add a comment |

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1 Answer
1

active

oldest

votes

1 Answer
1

active

oldest

votes

Because pthread_join(thread_id, NULL); waits for the thread to finish. And a thread running a while (1) {} loop will never finish.

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

do I need the pthread_join(thread_id, NULL); line then? @MartinHeralecký

– Matt X
Nov 21 '18 at 21:29

@MattX If you don't put it there, the After Thread message will print immediately after starting the thread, which will keep running.

– Martin Heralecký
Nov 21 '18 at 21:31

If you changed the code in myThread to loop 10 times and print something out or sleep and then return, you'd wait for it to finish with the call to pthread_join in main. And after that your program could exit. If you just leave myThread as it is and take out the call to pthread_join, your program won't wait for the thread to finish and exit right away.

– bruceg
Nov 21 '18 at 21:36

@MattX Whether or not you need it depends on exactly what you're trying to do, which we do not know. What you should do depends on exactly what this thread is doing and how it relates to what the program as a whole is doing.

– David Schwartz
Nov 21 '18 at 21:39

add a comment |

Because pthread_join(thread_id, NULL); waits for the thread to finish. And a thread running a while (1) {} loop will never finish.

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

do I need the pthread_join(thread_id, NULL); line then? @MartinHeralecký

– Matt X
Nov 21 '18 at 21:29

@MattX If you don't put it there, the After Thread message will print immediately after starting the thread, which will keep running.

– Martin Heralecký
Nov 21 '18 at 21:31

If you changed the code in myThread to loop 10 times and print something out or sleep and then return, you'd wait for it to finish with the call to pthread_join in main. And after that your program could exit. If you just leave myThread as it is and take out the call to pthread_join, your program won't wait for the thread to finish and exit right away.

– bruceg
Nov 21 '18 at 21:36

@MattX Whether or not you need it depends on exactly what you're trying to do, which we do not know. What you should do depends on exactly what this thread is doing and how it relates to what the program as a whole is doing.

– David Schwartz
Nov 21 '18 at 21:39

add a comment |

Because pthread_join(thread_id, NULL); waits for the thread to finish. And a thread running a while (1) {} loop will never finish.

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

Because pthread_join(thread_id, NULL); waits for the thread to finish. And a thread running a while (1) {} loop will never finish.

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

answered Nov 21 '18 at 21:27

Martin Heralecký

3,11721134

do I need the pthread_join(thread_id, NULL); line then? @MartinHeralecký

– Matt X
Nov 21 '18 at 21:29

@MattX If you don't put it there, the After Thread message will print immediately after starting the thread, which will keep running.

– Martin Heralecký
Nov 21 '18 at 21:31

If you changed the code in myThread to loop 10 times and print something out or sleep and then return, you'd wait for it to finish with the call to pthread_join in main. And after that your program could exit. If you just leave myThread as it is and take out the call to pthread_join, your program won't wait for the thread to finish and exit right away.

– bruceg
Nov 21 '18 at 21:36

@MattX Whether or not you need it depends on exactly what you're trying to do, which we do not know. What you should do depends on exactly what this thread is doing and how it relates to what the program as a whole is doing.

– David Schwartz
Nov 21 '18 at 21:39

add a comment |

do I need the pthread_join(thread_id, NULL); line then? @MartinHeralecký

– Matt X
Nov 21 '18 at 21:29

@MattX If you don't put it there, the After Thread message will print immediately after starting the thread, which will keep running.

– Martin Heralecký
Nov 21 '18 at 21:31

If you changed the code in myThread to loop 10 times and print something out or sleep and then return, you'd wait for it to finish with the call to pthread_join in main. And after that your program could exit. If you just leave myThread as it is and take out the call to pthread_join, your program won't wait for the thread to finish and exit right away.

– bruceg
Nov 21 '18 at 21:36

@MattX Whether or not you need it depends on exactly what you're trying to do, which we do not know. What you should do depends on exactly what this thread is doing and how it relates to what the program as a whole is doing.

– David Schwartz
Nov 21 '18 at 21:39

do I need the pthread_join(thread_id, NULL); line then? @MartinHeralecký

– Matt X
Nov 21 '18 at 21:29

@MattX If you don't put it there, the After Thread message will print immediately after starting the thread, which will keep running.

– Martin Heralecký
Nov 21 '18 at 21:31

If you changed the code in myThread to loop 10 times and print something out or sleep and then return, you'd wait for it to finish with the call to pthread_join in main. And after that your program could exit. If you just leave myThread as it is and take out the call to pthread_join, your program won't wait for the thread to finish and exit right away.

– bruceg
Nov 21 '18 at 21:36

@MattX Whether or not you need it depends on exactly what you're trying to do, which we do not know. What you should do depends on exactly what this thread is doing and how it relates to what the program as a whole is doing.

– David Schwartz
Nov 21 '18 at 21:39

add a comment |

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