QPP (Promises Augmentation & Patterns)

Class: SemaphoreMultiReservation

SemaphoreMultiReservation

This is a class that provides promises enabled semaphores. It differs from the class Semaphore (@see qpp.Semaphore ) in a way it supports allocation of more than one resource in one wait() call

new SemaphoreMultiReservation(name, resourcesNo, debug, waitForMoreDemandingConsumers, debug)

Constructor function. Creates a new semaphore with optional name and resources number

Parameters:
Name Type Argument Default Description
name string <optional>
 "semaphore"

The name of the created semaphore
resourcesNo number(integer) <optional>
 1

The total numer of resources available
debug boolean <optional>
 false

Defines if debugging messages should be shown during Semaphore operations
waitForMoreDemandingConsumers boolean <optional>
 true

Defines if consumer can allocate resources even if other consumer waits for available resources (but needs more resources than currently available)
debug boolean <optional>
 false

Defines if debugging messages should be shown during Semaphore operations
Source:
Example
// Example of 3 groups
	var QPP = require('qpp');
	var s = new QPP.SemaphoreMultiReservation('Nebojsa tower', 5);
	
	// group 1
	setTimeout(function(){
		s.wait(3) // 3 people
		.then(function(){ // resource is available, consuming resource
			console.log("Group 1: Let's run to the top!");
			setTimeout(function(){
				console.log("Group 1: Great experience, but they ask us to leave!")
				s.signal(3); // releasing resource (toilet)
			}, parseInt(Math.random()*1500)+1);
		});
	}, parseInt(Math.random()*100)+1);
	
	// group 2
	setTimeout(function(){
		s.wait(4) // 4 people
		.then(function(){ // resource is available, consuming resource
			console.log("Group 2: Tower is available for us!");
			setTimeout(function(){
				console.log("Group 2: Let's give the space for others!")
				s.signal(4); // releasing resource (toilet)
			}, parseInt(Math.random()*500)+1);
		});
	}, parseInt(Math.random()*100)+1);
	
	// group 3
	setTimeout(function(){
		s.wait(2) // 2 people
		.then(function(){ // resource is available, consuming resource
			console.log("Group 3: Hey, i have to show you the view!");
			setTimeout(function(){
				console.log("Group 3: Ah, we could stay here forever!")
				s.signal(2); // releasing resource (toilet)
			}, parseInt(Math.random()*100)+1);
		});
	}, parseInt(Math.random()*100)+1);
	
	// This is the most interesting scenario:
	//		Group 2: Tower is available for us
	//		Group 2: Let's give the space for others
	//		Group 3: Hey, i have to show you the view
	//		Group 1: Let's run to the top
	//		Group 3: Ah, we could stay here forever
	//		Group 1: Great experience, but they ask us to leave!
	// Because both group 1 and 3 ended up at the top of the towe simultaneously
	// (there were enough of resources to allocate for both (2+3<=5))
	// 
	// For more examples, please check unit tests for @see qpp.mapBandwidth

Members

#debug :boolean

defines if debugging messages should be shown during Semaphore operations

Type:
  • boolean
Source:

#name :string

name of the semaphore

Type:
  • string
Source:

#resourcesNo :string

currently available number of resources

Type:
  • string
Source:

#waitForMoreDemandingConsumers :boolean

defines if consumer can allocate resources even if other consumer waits for available resources (but needs more resources than currently available)

Type:
  • boolean
Default Value:
  • true
Source:
Example
var s = new Semaphore('s', 3);
		var wP1 = s.wait(1); // fine, 2 resources left available
		var wP2 = s.wait(3); // not fine (consumer 1 has to release)
		// wP3 will be fine and resolved if this.waitForMoreDemandingConsumers === false
		// or not fine and not resolved until consumer 1's resources are released (signaled) 
		// if this.waitForMoreDemandingConsumers === true (default)
		var wP3 = s.wait(2);

Methods

signal(resourcesReleased)

release resources in semaphore

Parameters:
Name Type Argument Default Description
resourcesReleased number <optional>
 "1"

The numer of resources released
Source:

wait(resourcesNoNeeded)

waits on semaphore

Parameters:
Name Type Argument Default Description
resourcesNoNeeded number <optional>
 "1"

The numer of resources needed
Source:
Returns:

promise that will get resolved after the semaphore is available/ The only possibility for promise to get rejected is when semaphore gets destroyed In that case it will get rejected with an @see Error.

Type
external:Promise