FIFO deadlock problems (code included): deadlock, fifo, problems, code

FIFO deadlock problems (code included)

Hi, when I run the reader and then the writer (2 separate programs) I get deadlocked.
they both reach "fifo is now open!" and "reply is now open" but then they lock up.
if in the writer I don't try to read back, it works ok (marked with *troublemaker*).

my question is: why?

the write_str, read_to_zero functions served me well in the past.

thank you.

code:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

#include "general.h"

/*
writes a string to the fifo with '\0'.
returns number of chars written (including '\0').
*/
int write_str(char *str, FILE *fifo) {
size_t len = (strlen(str)+1)*sizeof(char);
if(fwrite(str,sizeof(char),len,fifo)>0)
return (int)len;
return FALSE;
}

/*
read from fifo until '\0'
return if input fits buffer
*/
int read_to_zero(FILE *fifo, char *buffer, int buff_size) {
int i, ch;
for(i=0;i<buff_size;i++) {
ch = fgetc(fifo);
if(ch==EOF)
return FALSE;
buffer[i] = (char)ch;
if(!buffer[i])
return TRUE;
}
while((ch=fgetc(fifo)) && (ch!=EOF))
;
return FALSE;
}

/* writer */

int main() {
pid_t writer;
int e;
FILE *fifo, *reply;
char buff[256];

remove("reply");
mkfifo("reply", S_IREAD | S_IWRITE);
writer = getpid();
sprintf(buff,"%d",writer);
fifo = fopen("the_fifo","w");
printf("fifo now open!\n");
reply = fopen("reply","r");
printf("reply now open!\n");
write_str(buff,fifo);
printf("wrote: %s\n", buff);
read_to_zero(reply,buff,256); // *troublemaker*
printf("reply: %s\n", buff);
}

/* reader */

int main() {
pid_t writer;
int e;
FILE *fifo, *reply;
char buff[256];

remove("the_fifo");
e = mkfifo("the_fifo", S_IREAD | S_IWRITE );
fifo = fopen("the_fifo","r");
printf("fifo now open!\n");
reply = fopen("reply","w");
printf("reply now open!\n");
read_to_zero(fifo,buff,256);
printf("read %d\n",writer);
write_str(buff,fifo);
}

/* the end */

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FIFO deadlock problems (code included)

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