?? lockmainubuf.c
字號:
#include "unpipc.h"
#define SEQFILE "seqno" /* filename */
void my_lock(int), my_unlock(int);
int
main(int argc, char **argv)
{
int fd, i, seqno, c;
pid_t pid;
ssize_t n;
char line[MAXLINE + 1], *ptr;
pid = getpid();
fd = Open(SEQFILE, O_RDWR | O_CREAT, FILE_MODE);
setvbuf(stdout, NULL, _IONBF, 0); /* unbuffered */
for (i = 0; i < 20; i++) {
my_lock(fd); /* lock the file */
Lseek(fd, 0L, SEEK_SET); /* rewind before read */
n = Read(fd, line, MAXLINE);
line[n] = '\0'; /* null terminate for sscanf */
n = sscanf(line, "%d\n", &seqno);
snprintf(line, sizeof(line), "pid = %d, seq# = %d\n", pid, seqno);
for (ptr = line; (c = *ptr++) != 0; )
putchar(c);
seqno++; /* increment sequence number */
sprintf(line, "%03d\n", seqno);
Lseek(fd, 0, SEEK_SET); /* rewind before write */
Write(fd, line, strlen(line));
my_unlock(fd); /* unlock the file */
}
exit(0);
}
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