Improve WIN32 waiting logic in psql's \watch command.

do_watch had some leftover logic for enabling siglongjmp out of
waiting for input.  That's never done anything on Windows (cf.
psql_cancel_callback), and do_watch no longer relies on it for
non-Windows, so let's drop it.

Also, when the user cancels \watch by pressing ^C, the Windows
code would run the query one more time before exiting.  That doesn't
seem very desirable, and it's not what happens on other platforms.
Use the "done" flag similarly to non-Windows to avoid the extra query
execution.

Yugo Nagata (with minor fixes by me)

Discussion: https://postgr.es/m/20240305220552.85fd4afd6b6b8103bf4fe3d0@sraoss.co.jp

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 5c906e480688b8135351ebb5190ac64c043ed500..9b0fa041f730c55f4890c08689c7ec99a4d47afd 100644 (file)
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -5173,12 +5173,12 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
    FILE       *pagerpipe = NULL;
    int         title_len;
    int         res = 0;
+   bool        done = false;
 #ifndef WIN32
    sigset_t    sigalrm_sigchld_sigint;
    sigset_t    sigalrm_sigchld;
    sigset_t    sigint;
    struct itimerval interval;
-   bool        done = false;
 #endif
 
    if (!query_buf || query_buf->len <= 0)
@@ -5260,7 +5260,6 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
    if (!pagerpipe)
        myopt.topt.pager = 0;
 
-
    /*
     * If there's a title in the user configuration, make sure we have room
     * for it in the title buffer.  Allow 128 bytes for the timestamp plus 128
@@ -5270,7 +5269,8 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
    title_len = (user_title ? strlen(user_title) : 0) + 256;
    title = pg_malloc(title_len);
 
-   for (;;)
+   /* Loop to run query and then sleep awhile */
+   while (!done)
    {
        time_t      timer;
        char        timebuf[128];
@@ -5305,6 +5305,7 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
        if (iter && (--iter <= 0))
            break;
 
+       /* Quit if error on pager pipe (probably pager has quit) */
        if (pagerpipe && ferror(pagerpipe))
            break;
 
@@ -5314,28 +5315,22 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
 #ifdef WIN32
 
        /*
-        * Set up cancellation of 'watch' via SIGINT.  We redo this each time
-        * through the loop since it's conceivable something inside
-        * PSQLexecWatch could change sigint_interrupt_jmp.
+        * Wait a while before running the query again.  Break the sleep into
+        * short intervals (at most 1s); that's probably unnecessary since
+        * pg_usleep is interruptible on Windows, but it's cheap insurance.
         */
-       if (sigsetjmp(sigint_interrupt_jmp, 1) != 0)
-           break;
-
-       /*
-        * Enable 'watch' cancellations and wait a while before running the
-        * query again.  Break the sleep into short intervals (at most 1s).
-        */
-       sigint_interrupt_enabled = true;
        for (long i = sleep_ms; i > 0;)
        {
            long        s = Min(i, 1000L);
 
            pg_usleep(s * 1000L);
            if (cancel_pressed)
+           {
+               done = true;
                break;
+           }
            i -= s;
        }
-       sigint_interrupt_enabled = false;
 #else
        /* sigwait() will handle SIGINT. */
        sigprocmask(SIG_BLOCK, &sigint, NULL);
@@ -5369,8 +5364,6 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
 
        /* Unblock SIGINT so that slow queries can be interrupted. */
        sigprocmask(SIG_UNBLOCK, &sigint, NULL);
-       if (done)
-           break;
 #endif
    }