Generic resource pooling for Node.JS
Generic resource pool. Can be used to reuse or throttle expensive resources such as database connections.
$ npm install generic-pool
The history has been moved to the CHANGELOG
// Create a MySQL connection pool with// a max of 10 connections, a min of 2, and a 30 second max idle timevar Pool = require'generic-pool'Pool;var mysql = require'mysql'; // v2.10.xvar pool =name : 'mysql'var c = mysqlcreateConnectionuser: 'scott'password: 'tiger'database:'mydb'// parameter order: err, resourcecallbacknull c;clientend;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 removedidleTimeoutMillis : 30000// if true, logs via console.log - can also be a functionlog : true;
// acquire connection - callback function is called// once a resource becomes availablepoolacquireif err// handle error - this is generally the err from your// factory.create functionelseclientquery"select * from foo"// return object back to poolpoolreleaseclient;;;
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.pooldrainpooldestroyAllNow;;
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 (Note: min==max case is expected to change in v3 release) 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), returnToHead : boolean, if true the most recently released resources will be the first to be allocated. This in effect turns the pool's behaviour from a queue into a stack. optional (default false) 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. validateAsync : Asynchronous validate function. Receives a callback function as its second argument, which should be called with a single boolean argument being true if the item is still valid and false if it should be removed from the pool. Called before item is acquired from pool. Default is undefined. Only one of validate/validateAsync may be specified 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 2var pool =name : 'mysql'// do something// cleanup. omitted for this examplemax : 10idleTimeoutMillis : 30000priorityRange : 3;// acquire connection - no priority - will go at front of line (same as high priority)poolacquirepoolreleaseclient;;// acquire connection - high priority - will go into front slotpoolacquirepoolreleaseclient;0;// acquire connection - medium priority - will go into middle slotpoolacquirepoolreleaseclient;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
One side-effect of calling
drain() is that subsequent calls to
will throw an Error.
To transparently handle object acquisition for a function,
one can use
var privateFn publicFn;publicFn = poolpooled// Do something with the client and arg. Client is auto-released when cb is calledcbnull 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 = poolpooled//Use client, assumed auto-release;publicTop = poolpooled// e.g., open a database transactionprivateBottomclient "arg"iferr return cberr;// e.g., close a transactioncb;;;
The following functions will let you get information about the pool:
// returns factory.name for this poolpoolgetName// returns number of resources in the pool regardless of// whether they are free or in usepoolgetPoolSize// returns number of unused resources in the poolpoolavailableObjectsCount// returns number of callers waiting to acquire a resourcepoolwaitingClientsCount// returns number of maxixmum number of resources allowed by ppolpoolgetMaxPoolSize// returns number of minimum number of resources allowed by ppolpoolgetMinPoolSize
$ npm install expresso $ npm test
The test runner runs every test in parallel, so tests cannot safely share resources. If a test fails, its thrown assertion error may bubble up and halt execution/cause failures in other running tests; these are spurious. If you have a failing test, try running it in isolation until you get it to pass.
The individual tests "wait" by repeatedly checking the condition in the
beforeExit callback. The test is marked as "passed" if the
callback runs successfully. Generally, this is accomplished by counting the
number of assertions and checking that all of the test's assertions have been
We use eslint and the
standard ruleset. At the moment linting is not done as part of the test suite but this will probably change in the future. You should ideally lint your code before making any PR's patches etc.
Becuase the linting tools require nodejs >=
0.10 but we test against
0.6 installation of the tools is done via
npm run lint-install. Some kind of optionalDevDependencies would be great!
$ npm run lint-install $ npm run lint
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