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Re: [PATCH] Enable sub-second timeout in zsystem flock
Hello,
dana (Saturday 2020-01-11):
> Here's a basic, almost-does-nothing test script for it. Obv need to change the
> expected error messages in the second test to whatever you decide on. You can
> run it with `make check TESTNUM=V13`
Thank you. Please find below a revised patch against 5.8. This is
still to enable fractional-seconds timeout and retry interval for
zsystem flock.
One thing about the tests: I've used the (...)& syntax to launch a
sub-shell in the background for concurrency checks. But does the test
script wait for sub-processes to finish between tests? If not, then we
may need to add a 0.1-second sleep after the 3rd test
("zsystem flock unsuccessful wait test") because it starts a sub-shell
that waits for 0.2 seconds ("zselect -t 20") but the rest of the test
times out on purpose after only 0.11 seconds; so the sub-shell will
still be holding the lock for 0.09 seconds.
Also note that the test script requires zselect in addition to zsystem,
because I needed something that would reliably sleep a fractional
number of seconds. The regular sleep command isn't guaranteed to
support that, AFAIK.
Thanks, best regards,
Cedric Ware.
diff -ruN zsh-5.8.orig/Doc/Zsh/mod_system.yo zsh-5.8/Doc/Zsh/mod_system.yo
--- zsh-5.8.orig/Doc/Zsh/mod_system.yo 2020-01-13 06:39:15.000000000 +0100
+++ zsh-5.8/Doc/Zsh/mod_system.yo 2020-03-08 18:39:32.672683779 +0100
@@ -166,7 +166,7 @@
printed in the last case, but the parameter tt(ERRNO) will reflect
the error that occurred.
)
-xitem(tt(zsystem flock) [ tt(-t) var(timeout) ] [ tt(-f) var(var) ] [tt(-er)] var(file))
+xitem(tt(zsystem flock) [ tt(-t) var(timeout) ] [ tt(-i) var(interval) ] [ tt(-f) var(var) ] [tt(-er)] var(file))
item(tt(zsystem flock -u) var(fd_expr))(
The builtin tt(zsystem)'s subcommand tt(flock) performs advisory file
locking (via the manref(fcntl)(2) system call) over the entire contents
@@ -196,9 +196,16 @@
By default the shell waits indefinitely for the lock to succeed.
The option tt(-t) var(timeout) specifies a timeout for the lock in
-seconds; currently this must be an integer. The shell will attempt
-to lock the file once a second during this period. If the attempt
-times out, status 2 is returned.
+seconds; fractional seconds are allowed. During this period, the
+shell will attempt to lock the file every var(interval) seconds
+if the tt(-i) var(interval) option is given, otherwise once a second.
+(This var(interval) is shortened before the last attempt if needed,
+so that the shell waits only until the var(timeout) and not longer.)
+If the attempt times out, status 2 is returned.
+
+(Note: var(interval) must be less than LONG_MAX microseconds.
+This is many millenia on 64-bit systems, but only about 35 minutes
+on 32-bit systems.)
If the option tt(-e) is given, the file descriptor for the lock is
preserved when the shell uses tt(exec) to start a new process;
diff -ruN zsh-5.8.orig/Src/Modules/system.c zsh-5.8/Src/Modules/system.c
--- zsh-5.8.orig/Src/Modules/system.c 2020-02-06 20:53:18.000000000 +0100
+++ zsh-5.8/Src/Modules/system.c 2020-03-08 18:43:02.756951315 +0100
@@ -532,6 +532,9 @@
{
int cloexec = 1, unlock = 0, readlock = 0;
zlong timeout = -1;
+ double timeout_tmp;
+ long timeout_retry = 1e6;
+ mnumber timeout_param;
char *fdvar = NULL;
#ifdef HAVE_FCNTL_H
struct flock lck;
@@ -583,7 +586,44 @@
} else {
optarg = *args++;
}
- timeout = mathevali(optarg);
+ timeout_param = matheval(optarg);
+ if (!(timeout_param.type & MN_FLOAT)) {
+ timeout_param.type = MN_FLOAT;
+ timeout_param.u.d = (double)timeout_param.u.l;
+ }
+ timeout_tmp = timeout_param.u.d * 1e6;
+ if ((timeout_tmp < 1) || (timeout_tmp > ZLONG_MAX / 2)) {
+ zwarnnam(nam, "flock: invalid timeout value");
+ return 1;
+ }
+ timeout = (zlong)timeout_tmp;
+ break;
+
+ case 'i':
+ /* retry interval in seconds */
+ if (optptr[1]) {
+ optarg = optptr + 1;
+ optptr += strlen(optarg) - 1;
+ } else if (!*args) {
+ zwarnnam(nam,
+ "flock: option %c requires "
+ "a numeric retry interval",
+ opt);
+ return 1;
+ } else {
+ optarg = *args++;
+ }
+ timeout_param = matheval(optarg);
+ if (!(timeout_param.type & MN_FLOAT)) {
+ timeout_param.type = MN_FLOAT;
+ timeout_param.u.d = (double)timeout_param.u.l;
+ }
+ timeout_tmp = timeout_param.u.d * 1e6;
+ if ((timeout_tmp < 1) || (timeout_tmp > LONG_MAX)) {
+ zwarnnam(nam, "flock: invalid interval value");
+ return 1;
+ }
+ timeout_retry = (long)timeout_tmp;
break;
case 'u':
@@ -647,7 +687,8 @@
lck.l_len = 0; /* lock the whole file */
if (timeout > 0) {
- time_t end = time(NULL) + (time_t)timeout;
+ zlong now;
+ zlong end = time_clock_us() + timeout;
while (fcntl(flock_fd, F_SETLK, &lck) < 0) {
if (errflag) {
zclose(flock_fd);
@@ -658,11 +699,15 @@
zwarnnam(nam, "failed to lock file %s: %e", args[0], errno);
return 1;
}
- if (time(NULL) >= end) {
+ now = time_clock_us();
+ if (now >= end) {
zclose(flock_fd);
return 2;
}
- sleep(1);
+ if (now + timeout_retry > end) {
+ timeout_retry = end - now;
+ }
+ zsleep(timeout_retry);
}
} else {
while (fcntl(flock_fd, timeout == 0 ? F_SETLK : F_SETLKW, &lck) < 0) {
diff -ruN zsh-5.8.orig/Src/utils.c zsh-5.8/Src/utils.c
--- zsh-5.8.orig/Src/utils.c 2020-01-13 06:39:15.000000000 +0100
+++ zsh-5.8/Src/utils.c 2020-03-08 18:43:02.756951315 +0100
@@ -2745,6 +2745,26 @@
}
/*
+ * Return the current time in microseconds, using the system's
+ * monotonic clock if supported, the wall clock if not.
+ */
+
+/**/
+zlong
+time_clock_us(void)
+{
+#if defined(HAS_CLOCK_GETTIME) && defined(CLOCK_MONOTONIC)
+ struct timespec ts;
+ clock_gettime(CLOCK_MONOTONIC, &ts);
+ return ts.tv_sec * (zlong)1e6 + ts.tv_nsec / 1000;
+#else
+ struct timeval tv;
+ gettimeofday(&tv, NULL);
+ return tv.tv_sec * (zlong)1e6 + tv.tv_usec;
+#endif
+}
+
+/*
* Sleep for the given number of microseconds --- must be within
* range of a long at the moment, but this is only used for
* limited internal purposes.
diff -ruN zsh-5.8.orig/Test/V13system.ztst zsh-5.8/Test/V13system.ztst
--- zsh-5.8.orig/Test/V13system.ztst 1970-01-01 01:00:00.000000000 +0100
+++ zsh-5.8/Test/V13system.ztst 2020-03-08 19:04:56.550666311 +0100
@@ -0,0 +1,98 @@
+# Test zsh/system module
+
+%prep
+
+ if zmodload -s zsh/system && zmodload -s zsh/zselect; then
+ tst_dir=V13.tmp
+ mkdir -p -- $tst_dir
+ else
+ ZTST_unimplemented='the zsh/system and zsh/zselect modules are not available'
+ fi
+
+%test
+
+ (
+ : > $tst_dir/file
+ zsystem flock -t 0.1 -i 0.000001 $tst_dir/file
+ )
+0:zsystem flock valid time arguments
+
+ (
+ zsystem flock -t -1 $tst_dir/file ||
+ zsystem flock -t 0.49e-6 $tst_dir/file ||
+ zsystem flock -t 1e100 $tst_dir/file ||
+ zsystem flock -i -1 $tst_dir/file ||
+ zsystem flock -i 0.49e-6 $tst_dir/file ||
+ zsystem flock -i 1e100 $tst_dir/file
+ )
+1:zsystem flock invalid time arguments
+?(eval):zsystem:2: flock: invalid timeout value
+?(eval):zsystem:3: flock: invalid timeout value
+?(eval):zsystem:4: flock: invalid timeout value
+?(eval):zsystem:5: flock: invalid interval value
+?(eval):zsystem:6: flock: invalid interval value
+?(eval):zsystem:7: flock: invalid interval value
+
+ (
+ (zsystem flock $tst_dir/file && zselect -t 20) &
+ zselect -t 1
+ zsystem flock -t 0.1 $tst_dir/file
+ )
+2:zsystem flock unsuccessful wait test
+
+ (
+ typeset -F SECONDS
+ start=$SECONDS
+ (zsystem flock $tst_dir/file && zselect -t 50) &
+ zselect -t 1
+ if zsystem flock $tst_dir/file; then
+ elapsed=$[ $SECONDS - $start ]
+ if [[ $elapsed -ge 0.3 && $elapsed -le 0.7 ]]; then
+ echo "elapsed time seems OK" 1>&2
+ else
+ echo "elapsed time $elapsed should be ~ 0.5 second" 1>&2
+ fi
+ else
+ false
+ fi
+ )
+0:zsystem flock successful wait test, no timeout
+?elapsed time seems OK
+
+ (
+ typeset -F SECONDS
+ start=$SECONDS
+ (zsystem flock $tst_dir/file && zselect -t 50) &
+ zselect -t 1
+ if zsystem flock -t 1 $tst_dir/file; then
+ elapsed=$[ $SECONDS - $start ]
+ if [[ $elapsed -ge 0.9 && $elapsed -le 1.1 ]]; then
+ echo "elapsed time seems OK" 1>&2
+ else
+ echo "elapsed time $elapsed should be ~ 1.01 second" 1>&2
+ fi
+ else
+ false
+ fi
+ )
+0:zsystem flock successful wait test, integral seconds
+?elapsed time seems OK
+
+ (
+ typeset -F SECONDS
+ start=$SECONDS
+ (zsystem flock $tst_dir/file && zselect -t 25) &
+ zselect -t 1
+ if zsystem flock -t 0.4 -i 0.1 $tst_dir/file; then
+ elapsed=$[ $SECONDS - $start ]
+ if [[ $elapsed -ge 0.2 && $elapsed -le 0.5 ]]; then
+ echo "elapsed time seems OK" 1>&2
+ else
+ echo "elapsed time $elapsed should be ~ 0.3 second" 1>&2
+ fi
+ else
+ false
+ fi
+ )
+0:zsystem flock successful wait test, fractional seconds
+?elapsed time seems OK
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