lockfn

(c)Bumblehead MIT-license

A collection of function locks through which asynchronous code may be controlled.

• lockfn.queuing
• lockfn.caching
• lockfn.expiring
• lockfn.rebounding
• lockfn.throttling

• lockfn.caching Most common lock. Obtain data once for multiple callers.

  A template applied to each item of a list view will be requested once only:

  gettpl = (tplname, fn) => {
    server_request(tplname, (err, tpl) => {
       fn(err, tpl); // tpl is '<b>tpl</b>'
    });
  };
  gettplcache = lockfn.caching((tplname, fn) => {
    gettpl(tplname, fn)
  };
  gettplcache('listitem.mustache', (err, tpl) => {
    console.log('tpl is ' + tpl);        // tpl is <b>item</b>
  });
  gettplcache('listitem.mustache', (err, tplcached) => {
    console.log('tpl is ' + tplcached);  // tpl is <b>item</b>
  });

  This list uses different templates and unique templates are requested once only:

  // difference between lockfn.caching and lockfn.caching.namespace...
  //
  //   lockfn.caching: the first value obtained is returned to all callers.
  //   if 'lakelistitem.mustache' is obtained first, it is returned to all
  //   callers.
  //
  //   lockfn.caching.namespace: applies caching to values unique to string
  //   param given before the callback. Here 'lakelistitem.mustache' returns a
  //   cached value to calls for 'lakelistitem.mustache'. A different value is
  //   requested and cached for 'countrylistitem.mustache':
  gettplcache = lockfn.caching.namespace((tplname, fn) => {
    gettpl(tplname, fn)
  };
  gettplcache('lakelistitem.mustache', (err, tpl) => {
    console.log('tpl is ' + tpl);       // tpl is <b>lake</b>
  });
  gettplcache('lakelistitem.mustache', (err, tplcached) => {
    console.log('tpl is ' + tplcached); // tpl is <b>lake</b>
  });
  gettplcache('countrylistitem.mustache', (err, ctpl) => {
    console.log('tpl is ' + tpl);       // tpl is <b>country</b>
  });
  gettplcache('countrylistitem.mustache', (err, ctplcached) => {
    console.log('tpl is ' + tplcached); // tpl is <b>country</b>
  });

  Use multiple params with functions returned by lockfn.caching and lockfn.caching.namespace. Both require a callback as last parameter. lockfn.caching.namespace requires a string as the second-to-last parameter (a namespace for which the cache is held).

  gettplcache = lockfn.caching.namespace((session, cfg, tplname, fn) => {
    gettpl(tplname, fn)
  };
  gettplcache(session, cfg, 'nav.mustache', (err, tpl) => {
    console.log('tpl is ' + tpl);      // tpl is <b>nav</b>
  });
  gettplcache(session, cfg, 'nav.mustache', (err, tplcache) => {
    console.log('tpl is ' + tplcache); // tpl is <b>nav</b>
  });
  gettplcache(session, cfg, 'foot.mustache', (err, tplcache) => {
    console.log('tpl is ' + tplcache); // tpl is <b>foot</b>
  });

  Clear the cache and request the template anew

  gettplcache = lockfn.caching.namespace((session, cfg, tplname, fn) => {
    gettpl(tplname, fn)
  };
  session = 'english';
  gettplcache(session, cfg, 'bathroom.mustache', (err, tpl) => {
    console.log(tpl);      // <b>i need the bathroom</b>
  });
  session = 'spanish';
  gettplcache(session, cfg, 'bathroom.mustache', (err, tplcache) => {
    console.log(tplcache); // <b>i need the bathroom</b>
  });
  gettplcache.clear();
  gettplcache(session, cfg, 'bathroom.mustache', (err, tpl) => {
    console.log(tpl);      // <b>puedo ir al bano</b>
  });
  session = 'english';
  gettplcache(session, cfg, 'bathroom.mustache', (err, tpl) => {
    console.log(tpl);      // <b>puedo ir al bano</b>
  });

• lockfn.expiring Auto-call a function after given period of time has passed. If a function waits on a response from a server -auto-call that function after a few seconds (and do not allow future calls to the function).

  lockfn.expiring(function callmeafter5sec () {
    console.log('called in 5 seconds or less');
  }, 5000);

• lockfn.queuing Avoid stack overflow. Control caller access to a function that adds numerous frames to the stack by queuing calls so each completes before next begins:

getdecryptedblobqueue = lockfn.queuing((cipher, fn) => {
  fn(null, busydecryption(cipher)); // busydecryption adds numerous frames
});
getdecryptedblobqueue(cipher, (plain) => {
  console.log(plain); // long string
});
getdecryptedblobqueue(cipher, (plain) => {
  console.log(plain); // long string
}); 

Like lockfn.caching, a callback is required as the last parameter. Other params given in calls to the lock are passed to the function the lock was constructed around.

getdecryptedblobqueue = lockfn.queuing((cipher, key, type, fn) => {
  fn(null, busydecryption(cipher, key, type));
});
getdecryptedblobqueue(cipher, key, type, (plain) => {
  console.log(plain); // long string
});

• lockfn.rebounding A returned function handles one call, ignoring other calls until the first returns. Useful for handling form submit events, where a form should be submitted once only amid multiple submit events.

  Like lockfn.caching, a callback is given as the last parameter but is not required.

// the following would print 'submit one' only
rebound = lockrebound((arg1, arg2, exitfn) => {
  setTimeout(function () { 
    console.log('submit one');  // submit one
    exitfn(1, 2) 
  }, 200);
});
rebound('a', 'b', (num1, num2) => {
  console.log(num1, num2); // 1 2
});
rebound('a', 'b', (num1, num2) => {
  console.log(num1, num2); // not called
});
rebound('a', 'b'); // not called
setTimeout(() => { rebound('a', 'b'); }, 220); // is called

• lockfn.throttling A returned function handles first and last calls made within a specified amount of time. Other calls during that time are ignored. Limit calls which may be triggered rapidly many times. For example ,

  The following would print 'rain', 'spain', then 'plain':

  lockthrottle = lockfn.throttling({ ms : 500 });
  lockthrottle(() => { console.log('rain') });  // rain
  lockthrottle(() => { console.log('in') });
  lockthrottle(() => { console.log('spain') }); // spain
  lockthrottle(() => {
    setTimeout(() => {
      console.log('plain') };                         // plain
    }, 600)
  });

How:

Locks here are simple but effective due to the execution model found in various ECMAScript environments. Messages are handled in a queue sequentially, protecting the space in one lock call from calls made before or afterward.

(The MIT License)

Copyright (c) Bumblehead [email protected]

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