Implement 'release' event and 'activeCount' property.

index.js

@@ -44,8 +44,9 @@ function release (client, err) {
       this._remove(client)
     }, this.options.idleTimeoutMillis)
   }
-
   this._idle.push(new IdleItem(client, tid))
+  this._active.splice(this._active.indexOf(client), 1)
+  this.emit('release', client)
   this._pulseQueue()
 }
 
@@ -94,6 +95,7 @@ class Pool extends EventEmitter {
 
     this._clients = []
     this._idle = []
+    this._active = []
     this._pendingQueue = []
     this._endCallback = undefined
     this.ending = false
@@ -250,6 +252,7 @@ class Pool extends EventEmitter {
       } else {
         this.log('new client connected')
         client.release = release.bind(this, client)
+        this._active.push(client)
         this.emit('connect', client)
         this.emit('acquire', client)
         if (!pendingItem.timedOut) {
@@ -328,5 +331,9 @@ class Pool extends EventEmitter {
   get totalCount () {
     return this._clients.length
   }
+
+  get activeCount () {
+    return this._active.length
+  }
 }
 module.exports = Pool

test/events.js

@@ -60,6 +60,30 @@ describe('events', function () {
     }, 100)
   })
 
+  it('emits release every time a client is released', function (done) {
+    const pool = new Pool()
+    let releaseCount = 0
+    pool.on('release', function (client) {
+      expect(client).to.be.ok()
+      releaseCount++
+    })
+    for (let releases = [], i = 0; i < 10; i++) {
+      pool.connect(function (err, client, release) {
+        if (err) return done(err)
+        releases.push(release)
+        expect(pool.activeCount).to.be(releases.length)
+        if (releases.length === 10) {
+          while (releases.length > 0) releases.pop()()
+        }
+      })
+    }
+    setTimeout(function () {
+      expect(releaseCount).to.be(10)
+      expect(pool.activeCount).to.be(0)
+      pool.end(done)
+    }, 100)
+  })
+
   it('emits error and client if an idle client in the pool hits an error', function (done) {
     const pool = new Pool()
     pool.connect(function (err, client) {