Generic resource pool. Can be used to reuse or throttle expensive resources such as database connections. The e2e-transaction-logger can be used as the transaction object is propagated from the pool calls to the resource factory.
$ npm install e2e-generic-pool
// Create a MySQL connection pool with
// a max of 10 connections, a min of 2, and a 30 second max idle time
var poolModule = require('generic-pool');
var pool = poolModule.Pool({
name : 'mysql',
create : function(callback, trx) {
var io;
var Client = require('mysql').Client;
var c = new Client();
c.user = 'scott';
c.password = 'tiger';
c.database = 'mydb';
if(trx){ io = trx.startIO('CONNECT', 'MYSQL', d.database); } // use trx inside factory to log IOs
c.connect(function(err){
if(io){ io.end( (err) ? false : true); }
// parameter order: err, resource
callback(err, c);
});
},
destroy : function(client, trx) {
var io;
if(trx){ io = trx.startIO('DISCONNECT', 'MYSQL', c.database); }
client.end();
if(io){ io.end(); }
},
max : 10,
// optional. if you set this, make sure to drain() (see step 3)
min : 2,
// specifies how long a resource can stay idle in pool before being removed
idleTimeoutMillis : 30000,
// if true, logs via console.log - can also be a function
log : true
});// acquire connection - callback function is called
// once a resource becomes available
pool.acquire(trx, function(err, client) {
if (err) {
// handle error - this is generally the err from your
// factory.create function
}
else {
if(trx){ io = trx.startIO('SELECT', 'MYSQL', client.database); }
client.query("select * from foo", [], function(err, data) {
if(io){ io.end( (err) ? false : true); }
// return object back to pool
pool.release(client);
});
}
});If you are shutting down a long-lived process, you may notice that node fails to exit for 30 seconds or so. This is a side effect of the idleTimeoutMillis behavior -- the pool has a setTimeout() call registered that is in the event loop queue, so node won't terminate until all resources have timed out, and the pool stops trying to manage them.
This behavior will be more problematic when you set factory.min > 0, as the pool will never become empty, and the setTimeout calls will never end.
In these cases, use the pool.drain() function. This sets the pool into a "draining" state which will gracefully wait until all idle resources have timed out. For example, you can call:
// Only call this once in your application -- at the point you want
// to shutdown and stop using this pool.
pool.drain(function() {
pool.destroyAllNow(trx);
});If you do this, your node process will exit gracefully.
Pool() accepts an object with these slots:
name : name of pool (string, optional)
create : function that returns a new resource
should call callback() with the created resource
destroy : function that accepts a resource and destroys it
max : maximum number of resources to create at any given time
optional (default=1)
min : minimum number of resources to keep in pool at any given time
if this is set > max, the pool will silently set the min
to factory.max - 1
optional (default=0)
refreshIdle : boolean that specifies whether idle resources at or below the min threshold
should be destroyed/re-created. optional (default=true)
idleTimeoutMillis : max milliseconds a resource can go unused before it should be destroyed
(default 30000)
reapIntervalMillis : frequency to check for idle resources (default 1000),
priorityRange : int between 1 and x - if set, borrowers can specify their
relative priority in the queue if no resources are available.
see example. (default 1)
validate : function that accepts a pooled resource and returns true if the resource
is OK to use, or false if the object is invalid. Invalid objects will be destroyed.
This function is called in acquire() before returning a resource from the pool.
Optional. Default function always returns true.
log : true/false or function -
If a log is a function, it will be called with two parameters:
- log string
- log level ('verbose', 'info', 'warn', 'error')
Else if log is true, verbose log info will be sent to console.log()
Else internal log messages be ignored (this is the default)
The pool now supports optional priority queueing. This becomes relevant when no resources
are available and the caller has to wait. acquire() accepts an optional priority int which
specifies the caller's relative position in the queue.
// create pool with priorityRange of 3
// borrowers can specify a priority 0 to 2
var pool = poolModule.Pool({
name : 'mysql',
create : function(callback, trx) {
// do something
},
destroy : function(client, trx) {
// cleanup. omitted for this example
},
max : 10,
idleTimeoutMillis : 30000,
priorityRange : 3
});
// acquire connection - no priority - will go at end of line
pool.acquire(trx, function(err, client) {
pool.release(client);
});
// acquire connection - high priority - will go into front slot
pool.acquire(trx, function(err, client) {
pool.release(client);
}, 0);
// acquire connection - medium priority - will go into middle slot
pool.acquire(trx, function(err, client) {
pool.release(client);
}, 1);
// etc..If you know would like to terminate all the resources in your pool before
their timeouts have been reached, you can use destroyAllNow() in conjunction
with drain():
pool.drain(function() {
pool.destroyAllNow(trx);
});One side-effect of calling drain() is that subsequent calls to acquire()
will throw an Error.
To transparently handle object acquisition for a function,
one can use pooled():
var privateFn, publicFn;
publicFn = pool.pooled(privateFn = function(client, arg, cb) {
// Do something with the client and arg. Client is auto-released when cb is called
cb(null, arg);
});Keeping both private and public versions of each function allows for pooled functions to call other pooled functions with the same member. This is a handy pattern for database transactions:
var privateTop, privateBottom, publicTop, publicBottom;
publicBottom = pool.pooled(privateBottom = function(client, arg, cb) {
//Use client, assumed auto-release
});
publicTop = pool.pooled(privateTop = function(client, cb) {
// e.g., open a database transaction
privateBottom(client, "arg", function(err, retVal) {
if(err) { return cb(err); }
// e.g., close a transaction
cb();
});
});The following functions will let you get information about the pool:
// returns factory.name for this pool
pool.getName()
// returns number of resources in the pool regardless of
// whether they are free or in use
pool.getPoolSize()
// returns number of unused resources in the pool
pool.availableObjectsCount()
// returns number of callers waiting to acquire a resource
pool.waitingClientsCount()$ npm install expresso
$ expresso -I lib test/*.js
(The MIT License)
Copyright (c) 2010-2013 James Cooper <james@bitmechanic.com> Copyright (c) 2014 E2E Technologies Ltd
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