Hi Mikel,

Thanks for the kind words, this is the kind of feedback that make my day! ;-) It is always awsome to learn that your work end up being useful to the community!

Hi Gorenje,

Thanks you for reporting this. As explained in the article, SystemTimer was designed for a Rails application, so we did not bother implementing support for concurrent timers. Ruby on Rails was single-threaded at the time and we mostly wanted to solve our client's production problem.

Thanks to your post I started looking at what it would take to implement support for concurrent timers. The good news is that it can be done with a minimal impact of complexity. I finally found the time to work on it and I have just released SystemTimer 1.1 which provide full support for concurrent timers, including the scenario that you are describing.

Install it with sudo gem install SystemTimer and let me know if the new release works for you.

Hi Ahsan,

Thanks you for reporting this. As explained in my response to Gerenje, SystemTimer did not support concurrent timers at the time.

The good news is that SystemTimer 1.1 release fixes the problem and provide full support for concurrent timers. Install it with sudo gem install SystemTimer and let me know if the new release works for you.

Hi Jason,

Thanks you for reporting this. Please upgrade to SystemTimer 1.1 which fixes the problem and provide full support for concurrent timers. Install it with sudo gem install SystemTimer and let me know if the new release works for you.

Hi Chris,

Thanks a lot for looking into this and submitting your patch, appreciate it.

The root of the problem is that originally SystemTimer was not designed to support concurrent timers. So the patch is unfortunately treating the symptom more than the cause.

The good news though is that your post finally motivated me to evolve SystemTimer to a more generic solution, beyond its original Ruby on Rails lineage (where there is typically no re-entrant code). Full concurrent timer support is now implemented as part of SystemTimer 1.1. You can install it with sudo gem install SystemTimer and let me know if the new release works for you.

Thanks again, I have included your patch at the end of this post for reference:

    Index: ext/system_timer/system_timer_native.c
    ===================================================================
    --- ext/system_timer/system_timer_native.c      (revision 18927)
    +++ ext/system_timer/system_timer_native.c      (working copy)
    @@ -35,7 +35,7 @@
                   return Qnil;
           }
           clear_pending_sigalrm_for_ruby_threads();
    -       log_debug("install_timer: Succesfully blocked SIG_ALRM at O.S. level");
    +       log_debug("install_timer: Successfully blocked SIG_ALRM at O.S. level");
    
      /*
       * Save previous signal handler.
    @@ -46,7 +46,7 @@
                   restore_original_sigalrm_mask_when_blocked();
                   return Qnil;
      }
    -       log_debug("install_timer: Succesfully saved existing SIG_ALRM handler");
    +       log_debug("install_timer: Successfully saved existing SIG_ALRM handler");
    
           /*
            * Install Ruby Level SIG_ALRM handler
    @@ -75,7 +75,7 @@
                   restore_original_ruby_sigalrm_handler(self);
                   restore_original_sigalrm_mask_when_blocked();
           }
    -       log_debug("install_timer: Succesfully unblocked SIG_ALRM.");
    +       log_debug("install_timer: Successfully unblocked SIG_ALRM.");
    
           return Qnil;
     }
    @@ -98,9 +98,12 @@
    
    
           if (original_signal_handler.sa_handler == NULL) {
    -               log_error("cleanup_timer: Previous SIG_ALRM handler not initialized!", DO_NOT_DISPLAY_ERRNO);
    -       } else if (0 == sigaction(SIGALRM, &original_signal_handler, NULL)) {
    -               log_debug("cleanup_timer: Succesfully restored previous handler for SIG_ALRM");
    +               log_debug("cleanup_timer: No previous handler for SIG_ALRM, resetting to default");
    +               original_signal_handler.sa_handler = SIG_DFL;
    +               set_itimerval(&original_timer_interval, 0);
    +       }
    +       if (0 == sigaction(SIGALRM, &original_signal_handler, NULL)) {
    +               log_debug("cleanup_timer: Successfully restored previous handler for SIG_ALRM");
      } else {
                   log_error("cleanup_timer: Could not restore previous handler for SIG_ALRM", DISPLAY_ERRNO);
           }
    @@ -187,7 +190,7 @@
     static void clear_pending_sigalrm_for_ruby_threads()
     {
           CHECK_INTS;
    -       log_debug("Succesfully triggered all pending signals at Green Thread level");
    +       log_debug("Successfully triggered all pending signals at Green Thread level");
     }
    
     static void init_sigalarm_mask()
    Index: ChangeLog
    ===================================================================
    --- ChangeLog   (revision 18927)
    +++ ChangeLog   (working copy)
    @@ -2,3 +2,13 @@
    
     * Initial Release
    
    +=== 1.0.1 / 2008-10-23
    +
    +* Fix issue where signal handler was not restored if we had not previously
    +  installed a handler.
    +
    +=== 1.0.2 / 2008-10-24
    +
    +* Fix spelling mistakes
    +* Fix restoring timeout interval if we had not previously installed a
    +  handler.
    Index: SystemTimer.gemspec
    ===================================================================
    --- SystemTimer.gemspec (revision 18927)
    +++ SystemTimer.gemspec (working copy)
    @@ -1,19 +1,19 @@
     Gem::Specification.new do |s|
      s.name = %q{SystemTimer}
    -  s.version = "1.0"
    +  s.version = "1.0.2"
    
      s.specification_version = 2 if s.respond_to? :specification_version=
    
      s.required_rubygems_version = Gem::Requirement.new(">= 0") if s.respond_to? :required_rubygems_version=
      s.autorequire = %q{system_timer}
    -  s.date = %q{2008-05-28}
    +  s.date = %q{2008-10-24}
      s.extensions = ["ext/system_timer/extconf.rb"]
      s.extra_rdoc_files = ["README"]
      s.files = ["COPYING", "LICENSE", "ChangeLog", "ext/system_timer/system_timer_native.c", "ext/system_timer/extconf.rb", "lib/system_timer.rb", "lib/system_timer_stub.rb", "test/all_tests.rb", "test/system_timer_test.rb", "README"]
      s.has_rdoc = true
      s.rdoc_options = ["--title", "SystemTimer", "--main", "README", "--line-numbers"]
      s.require_paths = ["lib"]
    -  s.rubygems_version = %q{1.0.1}
    +  s.rubygems_version = %q{1.0.2}
      s.summary = %q{Set a Timeout based on signals, which are more reliable than Timeout. Timeout is based on green threads.}
      s.test_files = ["test/all_tests.rb"]
     end