#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define agents 5
#define tickets 20
int sold=0;
int n;
pthread_mutex_t tick_lock = PTHREAD_MUTEX_INITIALIZER;
void* sell (void* data) {
int n_done = 1;
while(n_done) {
pthread_mutex_lock(&tick_lock);
if(sold < tickets) { sold++; scanf("%d", &n); } //LINE 20:If i remove that "scanf",then my print on line 35 doesn't work!!!//
else {n_done = 0; }
pthread_mutex_unlock(&tick_lock); } }
main() {
int i=0;
pthread_t tas[agents];
void* returnv[agents];
printf("miracle"); /////MY "problematic" "printf"...
for(i=0; i<agents; i++)
pthread_create(&tas, NULL, sell, NULL);
for(i=0; i<agents; i++)
pthread_join(tas, &returnv);
}
Stupid problem with my simple "multithread" program..
Author
Hi people...i have a stupid problem with a very simple multithread program i created...
Inside my "main" function(line 35),i have put a "printf("miracle");" statement....
However,the word "miracle" never appears...
Here's the weird part..(at least for me...)
When on line 20 ,i add the "scanf("%d", n);" command,then the previous "printf("miracle");" works fine!!!
Could someone please explain me WHY that happens?
Let me also say,that no matter WHERE i put my "print("miracle");" statement inside my "main",the outcome doesn't change...
Any ideas please?
Here's the code...
****************************************************************
[Edited by - law_order on November 26, 2004 5:35:10 PM]
I am not familiar with pthread.h but i can assure you the problem is not with print or scanf. Something is hanging before the output buffer is flushed, ie somewhere in your code a mutex is never released. Your scanf is forcing the main thread to wait for input; without it execution is passed to another thread that isn't released so the buffer can flush.
Author
Quote:Original post by body electric
I am not familiar with pthread.h but i can assure you the problem is not with print or scanf. Something is hanging before the output buffer is flushed, ie somewhere in your code a mutex is never released. Your scanf is forcing the main thread to wait for input; without it execution is passed to another thread that isn't released so the buffer can flush.
thanks a lot body electric for your answer.
i checked mycode again and again,but i can't find any mistake...
obviously something escapes from me..
i can't really underestand why "printf" doesn't work...
it is put even BEFORE any new threads except "main" are created...
any other help would be really appreciated...
I ran this code on my MacOS X and Solaris boxen and could not reproduce your problem. I removed the scanf line and the printf was called as expected. This may be an implementation-specific issue.
Author
Quote:Original post by igni ferroque
I ran this code on my MacOS X and Solaris boxen and could not reproduce your problem. I removed the scanf line and the printf was called as expected. This may be an implementation-specific issue.
really igni?
i run my code on Mandrake Linux 8.2 AND WINDOWS XP with Cygwin installed...
Unfortunately,i always had the same problem...
thanks a lot anyway igni.
oh...and i compiled my code with the gcc compiler using the "-lpthread" option.
Just ran it on a Red Hat (kernel 2.2 I think) and HPUX box (with GCC and HP's C compiler). Worked fine all three times.
In the future when posting code, remember to use the [source][/source] tags.
In the future when posting code, remember to use the [source][/source] tags.
Author
Original post by igni ferroque
Just ran it on a Red Hat (kernel 2.2 I think) and HPUX box (with GCC and HP's C compiler). Worked fine all three times.
In the future when posting code, remember to use thetags.
i'm sorry...i'll remember that...
i'd like to ask one more a question...
if i put the "printf" statement at the end of my code (after the "pthread_join" "for" loop),what result should i see?
should the word "miracle" appear or not?
thanks again...
If you move the printf after the calls to pthread_join, printf won't be called until after the other threads finish. It will still be called.
Author
Quote:Original post by igni ferroque
If you move the printf after the calls to pthread_join, printf won't be called until after the other threads finish. It will still be called.
that's what i also thought...
thanks a lot...again...
This topic is closed to new replies.
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