debugging pipes

[kiros88]

Hey I had a question about pipes in programming form.

so if i had a main()
write(....,....., 10)

process 2
read(..., ...., 10)
read(..., ..., 10)

the code is at a halt I got because obviously u cant keep going until the the second read finally gets a second write() which i guess makes sense

but now lets say

so if i had a main()
write(....,"hello", 100)

process 2
read(..., ...., 100)
read(..., ..., 100)
exit(0)

the problem Im not sure about is that with write now sending in the pipe "hello" and the size i guess is obviously bigger then needed the program actually skips the second read and just exits out and I dont want it to exit. Y did the second read get skipped over just because the size had changed?

[Salem]

Are you actually checking the return results?

Because asking for 100 bytes is not the same as getting 100 bytes.

Buffer sizes on most read functions are a safe upper limit, not a demand.

[kiros88]

Okay well i tried to print out the pointer and got segmentation error but yea basically i can't stop the process from skipping the second read call.

[kiros88]

Okay so i justed check the return value and its -1....... which i guess is an error but cant figure it out.

#include <sys/types.h>
#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>


void * thread2(void*);
void * thread1(void*);

int	commpipe[2];		
int	sndpipe[2];
int rv, dv;
int looper,i ;
char buf [30]; 
char* bug;

#define NUM_THREADS 2
pthread_t tid[NUM_THREADS];      /* array of thread IDs */



int main(){



	char * buffer = "hello my tester\n";


	if (pipe( commpipe ) ) {
		fprintf(stderr,"Pipe error!\n");
		exit(1);
	}
	if (pipe( sndpipe ) ) {
		fprintf(stderr,"Pipe error!\n");
		exit(1);
	}
	pthread_create(&tid[1], NULL, thread1, NULL);
	pthread_create(&tid[0], NULL, thread2, NULL);
	write(sndpipe[1],buffer,100);
	//write(sndpipe[1],"hello test2 ",15);
	//write(sndpipe[1],"hello test 3",15);
	//write(sndpipe[1],"mark as test4",15);
	//sleep(7);
	write(commpipe[1], "test", 5);
		
	sleep(2);
	printf("Hello\n");
	sleep(2);
	printf("Goodbye\n");
	sleep(2);
	printf("exit\n");


	for ( i = 0; i < NUM_THREADS; i++)
    		pthread_join(tid[i], NULL);
	fprintf(stderr,"Child exited with a %d value\n",rv);
	return 0;
}

void * thread1(void* parm){

	sleep(5);
	read(commpipe[0], buf, 5);
	printf("%s  pipe output\n",buf);

	pthread_exit(0);

}

void* thread2(void* parm){
	sleep(6);
	read(sndpipe[0], bug,100);
	//printf("%s\n",bug);

	read(sndpipe[0], bug,100);
	//printf("%s\n",bug);
	for(looper =0; looper < 5; looper++){
	   sleep(1);
	   printf("GOSH\n");
	}
	pthread_exit(0);

}