Merge lp:~percona-toolkit-dev/percona-toolkit/pt-heartbeat-crashes-with-sleep-argument-1406390 into lp:~percona-toolkit-dev/percona-toolkit/release-2.2.14

[Frank Cizmich]

Problem:
pt-heartbeat was reported to fail sometimes when using --sleep option
Although unable to reproduce the code clearly showed a potential race condition where:
1) time function was tested to be over a certain fixed interval
2) a loop was entered waiting for next interval
3) on exiting the loop a sleep is issued with a potentially negative value due to the clock ticks transpiring after the exit of the loop

Solution:
Save the time value in a variable and use that value in the code to guarantee a positive value for the sleep function

[Daniel Nichter (daniel-nichter)]

Code comments are always helpful for the next person, e.g. in case someone runs into this code and wonders why the time is being saved in another var. Can also mention the bug/jira issue URL. Otherwise, code is fine.

review: Approve

[lp:~percona-toolkit-dev/percona-toolkit/pt-heartbeat-crashes-with-sleep-argument-1406390]

629. By Frank Cizmich on 2015-04-06

pt-heartbeat added comment for issue 1406390 fix

=== modified file 'bin/pt-heartbeat'
--- bin/pt-heartbeat	2015-01-23 10:19:56 +0000
+++ bin/pt-heartbeat	2015-04-06 21:22:41 +0000
@@ -5286,13 +5286,16 @@
    ) {
       eval {
          my $next_interval = $get_next_interval->();
-         if ( time >= $next_interval ) {
+         # save current time in variable to avoid race condition
+         # https://bugs.launchpad.net/percona-toolkit/+bug/1406390
+         my $time = time;
+         if ( $time >= $next_interval ) {
             do { $next_interval = $get_next_interval->() }
-               until $next_interval > time;
+               until $next_interval > $time;
             PTDEBUG && _d("Missed last interval; next interval:",
                ts($next_interval));
          }
-         sleep $next_interval - time;
+         sleep $next_interval - $time;
          PTDEBUG && _d('Woke up at', ts(time));
 
          # Connect or reconnect if necessary.
@@ -5419,13 +5422,16 @@
       PTDEBUG && _d('Checking slave', $dp->as_string($dsn));
 
       my $next_interval = $get_next_interval->();
-      if ( time >= $next_interval ) {
+      # save current time in variable to avoid race condition
+      # https://bugs.launchpad.net/percona-toolkit/+bug/1406390
+      my $time = time;
+      if ( $time >= $next_interval ) {
          do { $next_interval = $get_next_interval->() }
-            until $next_interval > time;
+            until $next_interval > $time;
          PTDEBUG && _d("Missed last interval; next interval:",
             ts($next_interval));
       }
-      sleep $next_interval - time;
+      sleep $next_interval - $time;
       PTDEBUG && _d('Woke up at', ts(time));
       my ($delay, $hostname, $master_server_id) = $get_delay->($sth);