Add a new tool Lock to lock a mutex.

And automaticlly unlock it when the `Lock` got out of scope.

include/tools/lock.h

@@ -0,0 +1,46 @@
+
+
+#ifndef KIWIXLIB_TOOL_LOCK_H
+#define KIWIXLIB_TOOL_LOCK_H
+
+#include <pthread.h>
+
+namespace kiwix {
+
+class Lock
+{
+  public:
+    explicit Lock(pthread_mutex_t* mutex) :
+      mp_mutex(mutex)
+    {
+      pthread_mutex_lock(mp_mutex);
+    }
+    ~Lock() {
+      if (mp_mutex != nullptr) {
+        pthread_mutex_unlock(mp_mutex);
+      }
+    }
+    Lock(Lock && other) :
+      mp_mutex(other.mp_mutex)
+    {
+      other.mp_mutex = nullptr;
+    }
+    Lock & operator=(Lock && other)
+    {
+      mp_mutex = other.mp_mutex;
+      other.mp_mutex = nullptr;
+      return *this;
+    }
+
+
+  private:
+    pthread_mutex_t* mp_mutex;
+
+    Lock(Lock const &) = delete;
+    Lock & operator=(Lock const &) = delete;
+};
+
+
+}
+
+#endif //KIWIXLIB_TOOL_LOCK_H