Refactored project structure.

src/ProcessControl/Factory.php

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+<?php
+
+namespace PHPCensor\ProcessControl;
+
+/**
+ * Construct an appropriate ProcessControl instance.
+ *
+ * @author Adirelle <adirelle@gmail.com>
+ */
+class Factory
+{
+    /**
+     * ProcessControl singleton.
+     *
+     * @var ProcessControlInterface
+     */
+    protected static $instance = null;
+
+    /**
+     * Returns the ProcessControl singleton.
+     *
+     * @return ProcessControlInterface
+     */
+    public static function getInstance()
+    {
+        if (static::$instance === null) {
+            static::$instance = static::createProcessControl();
+        }
+        return static::$instance;
+    }
+
+    /**
+     * Create a ProcessControl depending on available extensions and the underlying OS.
+     *
+     * Check PosixProcessControl, WindowsProcessControl and UnixProcessControl, in that order.
+     *
+     * @return ProcessControlInterface
+     *
+     * @throws \Exception
+     */
+    public static function createProcessControl()
+    {
+        switch (true) {
+            case PosixProcessControl::isAvailable():
+                return new PosixProcessControl();
+            case UnixProcessControl::isAvailable():
+                return new UnixProcessControl();
+        }
+
+        throw new \Exception("No ProcessControl implementation available.");
+    }
+}

src/ProcessControl/PosixProcessControl.php

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+<?php
+
+namespace PHPCensor\ProcessControl;
+
+/**
+ * Control process using the POSIX extension.
+ *
+ * @author Adirelle <adirelle@gmail.com>
+ */
+class PosixProcessControl implements ProcessControlInterface
+{
+    /**
+     * @param integer $pid
+     *
+     * @return bool
+     */
+    public function isRunning($pid)
+    {
+        // Signal "0" is not sent to the process, but posix_kill checks the process anyway;
+        return posix_kill($pid, 0);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function kill($pid, $forcefully = false)
+    {
+        return posix_kill($pid, $forcefully ? 9 : 15);
+    }
+
+    /**
+     * Check whether this posix_kill is available.
+     *
+     * @return bool
+     *
+     * @internal
+     */
+    public static function isAvailable()
+    {
+        return function_exists('posix_kill');
+    }
+}

src/ProcessControl/ProcessControlInterface.php

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+<?php
+
+namespace PHPCensor\ProcessControl;
+
+/**
+ * A stateless service to check and kill system processes.
+ *
+ * @author Adirelle <adirelle@gmail.com>
+ */
+interface ProcessControlInterface
+{
+    /**
+     * Checks if a process exists.
+     *
+     * @param int $pid The process identifier.
+     *
+     * @return boolean true is the process is running, else false.
+     */
+    public function isRunning($pid);
+
+    /**
+     * Terminate a running process.
+     *
+     * @param int $pid The process identifier.
+     * @param bool $forcefully Whether to gently (false) or forcefully (true) terminate the process.
+     *
+     * @return boolean
+     */
+    public function kill($pid, $forcefully = false);
+}

src/ProcessControl/UnixProcessControl.php

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+<?php
+
+namespace PHPCensor\ProcessControl;
+
+/**
+ * Control processes using the "ps" and "kill" commands.
+ *
+ * @author Adirelle <adirelle@gmail.com>
+ */
+class UnixProcessControl implements ProcessControlInterface
+{
+    /**
+     * Check process using the "ps" command.
+     *
+     * @param int $pid
+     *
+     * @return boolean
+     */
+    public function isRunning($pid)
+    {
+        $output = $exitCode = null;
+        exec(sprintf("ps %d", $pid), $output, $exitCode);
+        return $exitCode === 0;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function kill($pid, $forcefully = false)
+    {
+        $output = [];
+        $result = 1;
+        
+        exec(sprintf("kill -%d %d", $forcefully ? 9 : 15, $pid), $output, $result);
+        
+        return !$result;
+    }
+
+    /**
+     * Check whether the commands "ps" and "kill" are available.
+     *
+     * @return bool
+     *
+     * @internal
+     */
+    public static function isAvailable()
+    {
+        return DIRECTORY_SEPARATOR === '/' && exec("which ps") && exec("which kill");
+    }
+}