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index.js
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index.js
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'use strict';
var Promise = require('bluebird');
var PriorityQueue = require('js-priority-queue');
var cp = require('child_process');
var uuid = require('uuid');
var _ = require('lodash');
var Tadpole = (function () {
//Private Variables
var _initialized = false, _options, _addsPending = 0, _toRemove = 0, _addResolver;
/*
numChildren: In a single core environment, we'll still use one process and let the OS manage
resources. In a multicore environment, we'll leave one core for Node and use the rest for child processes.
*/
var _defaultOptions = {
numChildren: require('os').cpus().length -1 || 1,
priority: true,
addTimout: 30000,
env: process.env,
respawn: true
};
var _functionDefaults = {
priority: 100,
};
/*
A container for our child processes.
*/
var _children = {};
/*
This object is mainly for holding the resolver functions, but also keeps a record of each payload.
*/
var _inProcess = {};
var _functions = {};
var _queue = new PriorityQueue({comparator: function(a,b){ return a.priority - b.priority;}});
return {
spawn: function(userOptions){
if (_initialized) throw new Error('Cannot re-initialize Tadpole.');
userOptions = userOptions || {};
_.defaults(userOptions, _defaultOptions);
_options = userOptions;
for (var i = 0; i < userOptions.numChildren; i++){
addChild();
}
_initialized = true;
},
/*
Adds a function to the child processes.
@param {object} functionObject - An object literal with keys 'name' and 'func' representing
the function name and the function to be added.
*/
addFunction: function(functionObject) {
if (_addsPending > 0) throw new Error('Cannot add another function until previous add has completed.');
if (_functions[functionObject.name]) throw new Error('Already added a function with that name.');
if (functionObject.priority < 1) throw new Error('Priority less than 1 reserved for module use.');
if (!functionObject.func || !functionObject.name) throw new Error('Function object must contain both function and name.');
_.defaults(functionObject, _functionDefaults);
functionObject.func = stringifyFunction(functionObject.func); //dehydrate the function
functionObject.action = 'ADDFUNC';
_functions[functionObject.name] = functionObject;
_.each(_children, function(child){
injectFunction(functionObject, child);
});
return new Promise(function(resolve, reject){
_addResolver = resolve;
//TODO: reject if timeout elapses
});
},
/*
Runs a function with the supplied arguments.
@param {string} name - The name of the previously added function to run.
@param Optional - additional arguments to pass to the function.
*/
run: function(name){
var priority = _options.priority ? _functions[name].priority : 2;
var args = Array.prototype.slice.call(arguments, 1);
return new Promise(function(resolve, reject){
request({action: name,
priority: priority,
args: args,
resolver: resolve,
rejecter: reject
});
});
},
/*
Removes the specified number of child processes.
@param {number} num - The number of processes to remove, default 1.
*/
remove: function(num){
if (num < 1) throw new Error('Must provide value greater than 0 to remove.');
num = num || 1;
if (num > this.size()) num = this.size();
while(num){
_toRemove++;
if(!_queue.length) killChild();
num--;
}
},
/*
Adds the specified number of child processes.
@param {number} num - The number of processes to add, default 1.
*/
add: function(num){
num = num || 1;
while(num){
injectAllFunctions(addChild());
num--;
}
},
/*
Returns the current number of child processes.
*/
size: function(){
return Object.keys(_children).length;
},
/*
Kills all remaining child processes.
*/
killAll: function(){
if (_initialized){
this.remove(this.size());
_functions = {};
_initialized = false;
}
}
};
//Private functions
function stringifyFunction (func) {
return '(' + func + ')';
}
/*
This function is used by the module methods to process the result of each child process action,
and then get the next action from the queue.
*/
function next (childId, payload) {
//use the IDs to retrieve the payload from our storage in this process
var sentPayload = _inProcess[payload.id];
if (payload.error){
sentPayload.rejecter(payload.error);
return;
}
if (sentPayload.action === 'ADDFUNC') {
_addsPending--;
if (_addsPending === 0) _addResolver(true);
} else {
sentPayload.resolver(payload.result); //resolve those promises!
}
delete _inProcess[payload.id]; //no memory leaks please
//take this child out of service if we want to decrement running processes
if (_toRemove) {
killChild(childId);
return;
}
try{
var nextPayload = _queue.dequeue();
_inProcess[nextPayload.id] = nextPayload;
_children[childId].child.send(nextPayload);
} catch(err){
//empty queue throws error
_children[childId].active = false; //if the queue is empty, this child can rest
}
}
function setId(payload){
payload.id = uuid.v4();
}
function request (payload){
setId(payload);
if (_queue.length){ // if the queue is full, just enqueue the payload
_queue.queue(payload);
} else { //otherwise, let's find this payload a home!
var slotted = false;
_.each(_children, function(child, key){
if (!child.active){
_inProcess[payload.id] = payload;
child.active = true;
child.process.send(payload);
slotted = true;
return false; //if we've found a home, we stop the each loop
}
});
if (!slotted) _queue.queue(payload); //in case the queue was empty, but all the processes were working
}
}
function addChild(id){
id = id || uuid.v4();
var child = cp.fork(__dirname + '/child.js', {env: _options.env, execArgv: []});
child.on('error', function(error){
console.error('Error in child process: ' + error);
});
//when we get the result of reach transaction, this function is called to get the next operation in the queue
child.on('message', function(payload){
next(id, payload);
});
if (_options.respawn) {
child.on('exit', function(code, signal){
if (signal !== 'SIGTERM'){
addChild(id);
injectAllFunctions(child);
}
});
}
var container = {process: child, id: id, active: false};
_children[id] = container;
return id;
}
function injectFunction(functionObject, child){
// console.log('child', child);
_addsPending++;
setId(functionObject);
new Promise(function(resolve, reject) {
functionObject.resolver = resolve;
functionObject.rejecter = reject;
_inProcess[functionObject.id] = functionObject;
child.process.send(functionObject);
});
}
function injectAllFunctions(childId){
if (!_addsPending){
_.each(_functions, function(functionObject){
injectFunction(functionObject, _children[childId]);
});
} else setTimeout(function(){
injectAllFunctions(childId);
}, 500);
}
function killChild(childId){
if (childId){
_children[childId].process.kill();
delete _children[childId];
_toRemove--;
} else {
_.each(_children, function(child){
if (!child.active){
killChild(child.id);
return false; //we can stop once we get one
}
});
// we haven't killed the child, but there is still a value in _toRemove, so it should be killed when it finishes what it's working on
}
}
})();
module.exports = Tadpole;