[PATCH] Allow zsystem flock to query without second-lasting timeout

[PATCH] Allow zsystem flock to query without second-lasting timeout

[Sebastian Gniazdowski]

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Hello,
attached patch is dumb, and allows to use negative timeout, which
results in a quick (non-waiting) single fcntl() call. Such timeout can
already be passed to zsystem flock, because (Src/Modules/system.c):

                timeout = (time_t)mathevali(optarg);

and time_t is signed on Darwin, a linux box that a person tested and I
guess it's always signed because "time can be negative" – but a
knowledge here would be needed.

Best regards,
Sebastian Gniazdowski

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diff --git a/Src/Modules/system.c b/Src/Modules/system.c
index 1ee61c0..2769f75 100644
--- a/Src/Modules/system.c
+++ b/Src/Modules/system.c
@@ -636,7 +636,7 @@ bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
     lck.l_start = 0;
     lck.l_len = 0;  /* lock the whole file */
 
-    if (timeout > 0) {
+    if (timeout != 0) {
 	time_t end = time(NULL) + (time_t)timeout;
 	while (fcntl(flock_fd, F_SETLK, &lck) < 0) {
 	    if (errflag)

Re: [PATCH] Allow zsystem flock to query without second-lasting timeout

[Bart Schaefer]

On Sep 10,  5:49pm, Sebastian Gniazdowski wrote:
}
} attached patch is dumb, and allows to use negative timeout, which
} results in a quick (non-waiting) single fcntl() call.

I think a better approach would be to allow a zero timeout.  (Why was
there already a cast of time_t to time_t in the time(NULL) expression?)

Hopefully no one is already using the undocumented behavior that
"zsystem flock -t 0 ..." nevertheless waited forever.


diff --git a/Src/Modules/system.c b/Src/Modules/system.c
index 1ee61c0..afaec26 100644
--- a/Src/Modules/system.c
+++ b/Src/Modules/system.c
@@ -521,7 +521,7 @@ static int
 bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
 {
     int cloexec = 1, unlock = 0, readlock = 0;
-    time_t timeout = 0;
+    zlong timeout = -1;
     char *fdvar = NULL;
 #ifdef HAVE_FCNTL_H
     struct flock lck;
@@ -573,7 +573,7 @@ bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
 		} else {
 		    optarg = *args++;
 		}
-		timeout = (time_t)mathevali(optarg);
+		timeout = mathevali(optarg);
 		break;
 
 	    case 'u':
@@ -650,7 +650,7 @@ bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
 	    sleep(1);
 	}
     } else {
-	while (fcntl(flock_fd, F_SETLKW, &lck) < 0) {
+	while (fcntl(flock_fd, timeout == 0 ? F_SETLK : F_SETLKW, &lck) < 0) {
 	    if (errflag)
 		return 1;
 	    if (errno == EINTR)

Re: [PATCH] Allow zsystem flock to query without second-lasting timeout

[Sebastian Gniazdowski]

Really cool, thanks, I will use this via is-at-least, now I've
included cropped-down version of util-linux/flock in my plugin, it
amazingly compiles on OS X (so probably also FreeBSD), and of course
Linux

Best regards,
Sebastian Gniazdowski


On 10 September 2016 at 19:01, Bart Schaefer <schaefer@brasslantern.com> wrote:
> On Sep 10,  5:49pm, Sebastian Gniazdowski wrote:
> }
> } attached patch is dumb, and allows to use negative timeout, which
> } results in a quick (non-waiting) single fcntl() call.
>
> I think a better approach would be to allow a zero timeout.  (Why was
> there already a cast of time_t to time_t in the time(NULL) expression?)
>
> Hopefully no one is already using the undocumented behavior that
> "zsystem flock -t 0 ..." nevertheless waited forever.
>
>
> diff --git a/Src/Modules/system.c b/Src/Modules/system.c
> index 1ee61c0..afaec26 100644
> --- a/Src/Modules/system.c
> +++ b/Src/Modules/system.c
> @@ -521,7 +521,7 @@ static int
>  bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
>  {
>      int cloexec = 1, unlock = 0, readlock = 0;
> -    time_t timeout = 0;
> +    zlong timeout = -1;
>      char *fdvar = NULL;
>  #ifdef HAVE_FCNTL_H
>      struct flock lck;
> @@ -573,7 +573,7 @@ bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
>                 } else {
>                     optarg = *args++;
>                 }
> -               timeout = (time_t)mathevali(optarg);
> +               timeout = mathevali(optarg);
>                 break;
>
>             case 'u':
> @@ -650,7 +650,7 @@ bin_zsystem_flock(char *nam, char **args, UNUSED(Options ops), UNUSED(int func))
>             sleep(1);
>         }
>      } else {
> -       while (fcntl(flock_fd, F_SETLKW, &lck) < 0) {
> +       while (fcntl(flock_fd, timeout == 0 ? F_SETLK : F_SETLKW, &lck) < 0) {
>             if (errflag)
>                 return 1;
>             if (errno == EINTR)