Added option.maxTries

Setting this option stops trying to create resource after specified
consequent failures. Prevents pool going into infinite loop if resource
can not be created.

README.md

@@ -137,6 +137,7 @@ An optional object/dictionary with the any of the following properties:
 - `numTestsPerRun`: Number of resources to check each eviction run.  Default: 3.
 - `softIdleTimeoutMillis`: amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any), with the extra condition that at least "min idle" object instances remain in the pool. Default -1 (nothing can get evicted)
 - `idleTimeoutMillis`: the minimum amount of time that an object may sit idle in the pool before it is eligible for eviction due to idle time. Supercedes `softIdleTimeoutMillis` Default: 30000
+- `maxTries`: maximum number of consequent failures before pool stops trying to create resource and rejects resource request. Default: 0 (tries forever until resource is created).
 - `Promise`: Promise lib, a Promises/A+ implementation that the pool should use. Defaults to whatever `global.Promise` is (usually native promises).
 
 ### pool.acquire

lib/Pool.js

@@ -3,6 +3,7 @@
 const EventEmitter = require("events").EventEmitter;
 
 const factoryValidator = require("./factoryValidator");
+const errors = require('./errors')
 const PoolOptions = require("./PoolOptions");
 const ResourceRequest = require("./ResourceRequest");
 const ResourceLoan = require("./ResourceLoan");
@@ -123,6 +124,12 @@ class Pool extends EventEmitter {
      */
     this._scheduledEviction = null;
 
+    /**
+     * counter of consequent failures to create resource
+     * @type {Number}
+     */
+    this._failedTries = 0
+
     // create initial resources (if factory.min > 0)
     if (this._config.autostart === true) {
       this.start();
@@ -215,6 +222,15 @@ class Pool extends EventEmitter {
       return;
     }
 
+    // Try counter exceeded - reject resource request to next waiting client
+    if (
+      this._config.maxTries > 0 &&
+      this._failedTries >= this._config.maxTries
+    ) {
+      this._dispatchPooledResourceToNextWaitingClient()
+      return
+    }
+
     const resourceShortfall =
       numWaitingClients - this._potentiallyAllocableResourceCount;
 
@@ -267,15 +283,27 @@ class Pool extends EventEmitter {
     ) {
       // While we were away either all the waiting clients timed out
       // or were somehow fulfilled. put our pooledResource back.
-      this._addPooledResourceToAvailableObjects(pooledResource);
+      if (pooledResource) {
+        // While we were away either all the waiting clients timed out
+        // or were somehow fulfilled. put our pooledResource back.
+        this._addPooledResourceToAvailableObjects(pooledResource)
+      }
       // TODO: do need to trigger anything before we leave?
       return false;
     }
-    const loan = new ResourceLoan(pooledResource, this._Promise);
-    this._resourceLoans.set(pooledResource.obj, loan);
-    pooledResource.allocate();
-    clientResourceRequest.resolve(pooledResource.obj);
-    return true;
+    if (pooledResource) {
+      const loan = new ResourceLoan(pooledResource, this._Promise)
+      this._resourceLoans.set(pooledResource.obj, loan)
+      pooledResource.allocate()
+      clientResourceRequest.resolve(pooledResource.obj)
+    } else {
+      let errorMessage = 'Failed to create resource'
+      if (this._config.maxTries > 0 && this._failedTries >= this._config.maxTries) {
+        errorMessage = 'Failed to create resource ' + this._failedTries + ' times in a row'
+      }
+      clientResourceRequest.reject(new errors.ResourceCreationError(errorMessage))
+    }
+    return true
   }
 
   /**
@@ -304,12 +332,21 @@ class Pool extends EventEmitter {
    * @private
    */
   _createResource() {
+    // Do not attempt to create resource if reached maximum number of consequent failures
+    if (
+      this._config.maxTries > 0 &&
+      this._failedTries >= this._config.maxTries
+    ) {
+      return
+    }
     // An attempt to create a resource
     const factoryPromise = this._factory.create();
     const wrappedFactoryPromise = this._Promise.resolve(factoryPromise);
 
     this._trackOperation(wrappedFactoryPromise, this._factoryCreateOperations)
       .then(resource => {
+        // Resource created successfully - reset fail counter
+        this._failedTries = 0
         this._handleNewResource(resource);
         return null;
       })
@@ -435,6 +472,10 @@ class Pool extends EventEmitter {
       );
     }
 
+    // Reset fail counter - maybe resource will be created this time
+    // (for example network is restored and connection can be made)
+    this._failedTries = 0
+
     // TODO: should we defer this check till after this event loop incase "the situation" changes in the meantime
     if (
       this._config.maxWaitingClients !== undefined &&

lib/PoolOptions.js

@@ -42,6 +42,9 @@ class PoolOptions {
    * @param {Number} [opts.idleTimeoutMillis=30000]
    *   the minimum amount of time that an object may sit idle in the pool before it is eligible for eviction
    *   due to idle time. Supercedes "softIdleTimeoutMillis" Default: 30000
+   * @param {Number} opts.maxTries
+   *   maximum number of consequent failures before pool stops trying to create resource
+   *   and rejects resource request. Default: 0 (tries forever until resource is created).
    * @param {typeof Promise} [opts.Promise=Promise]
    *   What promise implementation should the pool use, defaults to native promises.
    */
@@ -81,9 +84,11 @@ class PoolOptions {
     this.max = parseInt(opts.max, 10);
     // @ts-ignore
     this.min = parseInt(opts.min, 10);
+    this.maxTries = parseInt(opts.maxTries, 10)
 
     this.max = Math.max(isNaN(this.max) ? 1 : this.max, 1);
     this.min = Math.min(isNaN(this.min) ? 0 : this.min, this.max);
+    this.maxTries = (isNaN(this.maxTries) ? 0 : this.maxTries)
 
     this.evictionRunIntervalMillis =
       opts.evictionRunIntervalMillis || poolDefaults.evictionRunIntervalMillis;

lib/errors.js

@@ -20,8 +20,15 @@ class TimeoutError extends ExtendableError {
     super(m);
   }
 }
+
+class ResourceCreationError extends ExtendableError {
+  constructor (m) {
+    super(m)
+  }
+}
 /* eslint-enable no-useless-constructor */
 
 module.exports = {
-  TimeoutError: TimeoutError
+  TimeoutError: TimeoutError,
+  ResourceCreationError: ResourceCreationError
 };