Package: manpages-dev
Version: 2.01-1
Severity: normal
The flock(2) man page says
A process may only hold one type of lock (shared or exclusive) on a
file. Subsequent flock() calls on an already locked file will convert
an existing lock to the new lock mode.
I read this as meaning the lock is associated with the process, and I
tried converting a lock through a second opened fd per the test
program below but it hung after printing "about to do second flock".
The lock is actually associated with the file table entry is it? Or
the table entry plus the process? Perhaps this can be clarified.
#include <stdio.h>
#include <sys/file.h>
int
main (void)
{
int x, y, ret;
x = open ("foo.tmp", O_RDWR | O_CREAT, 0666);
if (x == -1) perror ("first open");
ret = flock (x, LOCK_EX);
if (ret == -1) perror ("first flock");
y = open ("foo.tmp", O_RDWR);
if (y == -1) perror ("first open");
printf ("about to do second flock\n");
ret = flock (y, LOCK_SH);
if (ret == -1) perror ("second flock");
printf ("done\n");
return 0;
}
-- System Information:
Debian Release: 3.1
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: i386 (i586)
Kernel: Linux 2.6.8-1-386
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)
Versions of packages manpages-dev depends on:
ii manpages 2.01-1 Manual pages about using a GNU/Lin
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