Fix GC issues with closures for phpiredis reader handlers.

The following code, despite not being something you would do in real
world scenarios, eventually ended up generating an exception for "Too
many open files".

  for ($i = 0; $i < 10000; $i++) {
    $client = new Predis\Client();
    $client->connect();
  }

The reason was that the destructor for the connection was not invoked
by PHP as expected when the client instance went out of scope, so the
underlying stream resource were not being properly released.
Even without an actual "connect()" operation, the memory usage of PHP
kept growing until exhausting the configured value of max memory.

The source of the issue is related to the use of closures as handlers
for the phpiredis reader resource, to be more precise it seems to be
some kind of circular reference memory leak. Apparently PHP does not
like the fact that a closure, automatically bound to "$this" starting
with PHP 5.4, is stored in the reader resource which in turn is kept
referenced by "$this". This ends up the refcount not going down thus
the GC does not collect those connection objects going out of scope.
This is confirmed by the fact that this issue is not triggered when
using PHP 5.3 where the ZE does not automatically bind closures to
"$this", unless you capture "$this" with the "use()" directive (and
the usual "$that = $this" trick).

Using a static assignement instead of simply returning new closures
in "getStatusHandler()" and "getErrorHandler()" is kind of an hack
that seems to be working fine, the added value of this solution is
that we do not have to break the internal API of the three connection
backends based on ext-phpiredis.

This commit fixes #345.

CHANGELOG.md

@@ -9,6 +9,13 @@ v1.1.1 (2016-xx-xx)
   `connect()` on the redis-sentinel connection backend should fall back to the
   master connection instead of failing (ISSUE #342).
 
+- __FIX__: the two connection backends based on ext-phpiredis has some kind of
+  issues with the GC and the internal use of closures as reader callbacks that
+  prevented connections going out of scope from being properly collected and the
+  underlying stream or socket resources from being closed and freed. This should
+  not have had any actual effect in real-world scenarios due to the lifecycle of
+  PHP scripts, but we fixed it anyway (ISSUE #345).
+
 
 v1.1.0 (2016-06-02)
 ================================================================================

src/Connection/PhpiredisSocketConnection.php

@@ -143,11 +143,17 @@ class PhpiredisSocketConnection extends AbstractConnection
      *
      * @return \Closure
      */
-    private function getStatusHandler()
+    protected function getStatusHandler()
     {
-        return function ($payload) {
-            return StatusResponse::get($payload);
-        };
+        static $statusHandler;
+
+        if (!$statusHandler) {
+            $statusHandler = function ($payload) {
+                return StatusResponse::get($payload);
+            };
+        }
+
+        return $statusHandler;
     }
 
     /**
@@ -157,9 +163,15 @@ class PhpiredisSocketConnection extends AbstractConnection
      */
     protected function getErrorHandler()
     {
-        return function ($payload) {
-            return new ErrorResponse($payload);
-        };
+        static $errorHandler;
+
+        if (!$errorHandler) {
+            $errorHandler = function ($errorMessage) {
+                return new ErrorResponse($errorMessage);
+            };
+        }
+
+        return $errorHandler;
     }
 
     /**

src/Connection/PhpiredisStreamConnection.php

@@ -160,9 +160,15 @@ class PhpiredisStreamConnection extends StreamConnection
      */
     protected function getStatusHandler()
     {
-        return function ($payload) {
-            return StatusResponse::get($payload);
-        };
+        static $statusHandler;
+
+        if (!$statusHandler) {
+            $statusHandler = function ($payload) {
+                return StatusResponse::get($payload);
+            };
+        }
+
+        return $statusHandler;
     }
 
     /**
@@ -172,9 +178,15 @@ class PhpiredisStreamConnection extends StreamConnection
      */
     protected function getErrorHandler()
     {
-        return function ($errorMessage) {
-            return new ErrorResponse($errorMessage);
-        };
+        static $errorHandler;
+
+        if (!$errorHandler) {
+            $errorHandler = function ($errorMessage) {
+                return new ErrorResponse($errorMessage);
+            };
+        }
+
+        return $errorHandler;
     }
 
     /**

src/Connection/WebdisConnection.php

@@ -163,9 +163,15 @@ class WebdisConnection implements NodeConnectionInterface
      */
     protected function getStatusHandler()
     {
-        return function ($payload) {
-            return StatusResponse::get($payload);
-        };
+        static $statusHandler;
+
+        if (!$statusHandler) {
+            $statusHandler = function ($payload) {
+                return StatusResponse::get($payload);
+            };
+        }
+
+        return $statusHandler;
     }
 
     /**
@@ -175,9 +181,15 @@ class WebdisConnection implements NodeConnectionInterface
      */
     protected function getErrorHandler()
     {
-        return function ($payload) {
-            return new ErrorResponse($payload);
-        };
+        static $errorHandler;
+
+        if (!$errorHandler) {
+            $errorHandler = function ($errorMessage) {
+                return new ErrorResponse($errorMessage);
+            };
+        }
+
+        return $errorHandler;
     }
 
     /**