1 files changed, 107 insertions, 0 deletions
diff --git a/xbmc/threads/Lockables.h b/xbmc/threads/Lockables.h
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+/*
+ *  Copyright (C) 2005-2018 Team Kodi
+ *  This file is part of Kodi - https://kodi.tv
+ *
+ *  SPDX-License-Identifier: GPL-2.0-or-later
+ *  See LICENSES/README.md for more information.
+ */
+
+#pragma once
+
+namespace XbmcThreads
+{
+
+  /**
+   * This template will take any implementation of the "Lockable" concept
+   * and allow it to be used as an "Exitable Lockable."
+   *
+   * Something that implements the "Lockable concept" simply means that
+   * it has the three methods:
+   *
+   *   lock();
+   *   try_lock();
+   *   unlock();
+   *   IsLocked();
+   *
+   * "Exitable" specifically means that, no matter how deep the recursion
+   * on the mutex/critical section, we can exit from it and then restore
+   * the state.
+   *
+   * This requires us to extend the Lockable so that we can keep track of the
+   * number of locks that have been recursively acquired so that we can
+   * undo it, and then restore that (See class CSingleExit).
+   *
+   * All xbmc code expects Lockables to be recursive.
+   */
+  template<class L> class CountingLockable
+  {
+    friend class ConditionVariable;
+
+    CountingLockable(const CountingLockable&) = delete;
+    CountingLockable& operator=(const CountingLockable&) = delete;
+  protected:
+    L mutex;
+    unsigned int count = 0;
+
+  public:
+    inline CountingLockable() = default;
+
+    // STL Lockable concept
+    inline void lock() { mutex.lock(); count++; }
+    inline bool try_lock() { return mutex.try_lock() ? count++, true : false; }
+    inline void unlock() { count--; mutex.unlock(); }
+
+    /*!
+     * \brief Check if have a lock owned
+     * \return True if have a lock, otherwise false
+     */
+    inline bool IsLocked() const { return count > 0; }
+
+    /**
+     * This implements the "exitable" behavior mentioned above.
+     */
+    inline unsigned int exit(unsigned int leave = 0)
+    {
+      // it's possible we don't actually own the lock
+      // so we will try it.
+      unsigned int ret = 0;
+      if (try_lock())
+      {
+        if (leave < (count - 1))
+        {
+          ret = count - 1 - leave;  // The -1 is because we don't want
+                                    //  to count the try_lock increment.
+          // We must NOT compare "count" in this loop since
+          // as soon as the last unlock is called another thread
+          // can modify it.
+          for (unsigned int i = 0; i < ret; i++)
+            unlock();
+        }
+        unlock(); // undo the try_lock before returning
+      }
+
+      return ret;
+    }
+
+    /**
+     * Restore a previous exit to the provided level.
+     */
+    inline void restore(unsigned int restoreCount)
+    {
+      for (unsigned int i = 0; i < restoreCount; i++)
+        lock();
+    }
+
+    /**
+     * Some implementations (see pthreads) require access to the underlying
+     *  CCriticalSection, which is also implementation specific. This
+     *  provides access to it through the same method on the guard classes
+     *  UniqueLock, and SharedLock.
+     *
+     * There really should be no need for the users of the threading library
+     *  to call this method.
+     */
+    inline L& get_underlying() { return mutex; }
+  };
+
+}