graceful-critical

graceful-critical

A Nodejs package to handle graceful SIGHUP, SIGTERM and SIGINT around critical sections code. The package is designed to define critical sections by entering and exiting sections of code.

When a critical section is entered a unique exit function is returned. If the process receives a SIGHUP, SIGINT or SIGTERM, the package will wait for all critical sections to exit before calling a final exit callback. During shutdown, enter function calls will error, handled correctly this error can be used to prevent starting critical sections during shutdown.

Setup

const critical = require('graceful-critical');

Config

// Set the timeout milliseconds before process exit is forced.
critical.setExitTimeout(1000); // default 1000 // 0 for no timeout

// Set the number of panic count limit for consecutive ctrl-c calls before exit is forced.
critical.setPanicLimit(5); // default 5

critical.setExitCallback((processExit) => {
  // this will be called after all critical sections have exited.
  // it is not necessary to set this Callback
  processExit(); // calling processExit will finish exiting the process.
})

Usage

async function () {
  let exit;
  try {
    exit = critical.enter();

    /////////////////////
    //CRITICAL SECTION////
    /////////////////////

    exit();
  } catch (err) {
    if (err) // if critical.enter() throws an error the process is shuting down
    if (typeof exit === 'function') exit(); // remember to always exit even if you critical section throws an error.
  }
}

Usage - Callback

critical.enter((err, exit) => {
  if (err) // process is attempting to exit do not enter you critical section

  /////////////////////
  //CRITICAL SECTION////
  /////////////////////

  exit(); // pass this down your callback chain.
};

Exit Timeout

A timeout prevents the application from hanging due to improper code or zombie critical sections. This timeout will exit the process exit code 11. By default this timer is set to 1 second1 (1000). Setting the timer to 0 will disable the timer functionality. This timeout should be configured to properly accommodate for slow critical sections especially when critical sections could be blocked by long external resource calls.

Exit Panic

Another escape method is to use repeated SIGTERM/SIGTERM signals. This can be accomplished from the command line by repeating ctrl-c. The number of signals required to force an exit is configurable and by default set to 5.

Note: Process and container managers will send different signals when a process fails to exit promptly. The timing of which is usually configurable in these managers.

Exit Callback

Want to do one last thing before your process exits? setExitCallback allows a user defined function to be called before exiting.

TODO

• [] Exit and panic timeout before exit callbacks.
• [] Document various behaviors of process and container managers.
• [] Confirm signal selection

Contributing

Pull requests are welcome.