[core] Introduced the CSharedResource

srtcore/sync.cpp

@@ -353,3 +353,38 @@ int srt::sync::genRandomInt(int minVal, int maxVal)
 #endif // HAVE_CXX11
 }
 
+////////////////////////////////////////////////////////////////////////////////
+//
+// CSharedResource class
+//
+////////////////////////////////////////////////////////////////////////////////
+
+void srt::sync::CSharedResource::release()
+{
+    ScopedLock lock(m_lock);
+    SRT_ASSERT(m_iResourceTaken > 0);
+    --m_iResourceTaken;
+    if (m_iResourceTaken == 0)
+        m_cond.notify_one();
+}
+
+void srt::sync::CSharedResource::acquire()
+{
+    UniqueLock lock(m_lock);
+
+    // Allow reacquiring the resource from the same thread
+    if (m_iResourceTaken > 0 && this_thread::get_id() == m_thid)
+    {
+        ++m_iResourceTaken;
+        return;
+    }
+
+    while (m_iResourceTaken > 0)
+    {
+        m_cond.wait(lock);
+    }
+
+    SRT_ASSERT(m_iResourceTaken == 0);
+    ++m_iResourceTaken;
+    m_thid = this_thread::get_id();
+}

srtcore/sync.h

@@ -871,6 +871,56 @@ CUDTException& GetThreadLocalError();
 /// @param[in] minVal minimum allowed value of the resulting random number.
 /// @param[in] maxVal maximum allowed value of the resulting random number.
 int genRandomInt(int minVal, int maxVal);
+
+////////////////////////////////////////////////////////////////////////////////
+//
+// CSharedResource class
+//
+////////////////////////////////////////////////////////////////////////////////
+
+/// The class to synchronize acces to a shared resource.
+/// Can be acquired multiple times by the same thread.
+class CSharedResource
+{
+public:
+    CSharedResource()
+        : m_iResourceTaken(0)
+    {
+    }
+
+    /// Releases the shared resource. Can taken several times by the same thread,
+    /// therefore notifies another thread once finally release by this thread.
+    void release();
+
+    /// Acquires the shared resource. Can be acquired multiple times from the same thread,
+    /// would just increase the reference count. It the resource is taken, waits on a CV for a notification.
+    void acquire();
+
+private:
+    Mutex       m_lock;
+    Condition   m_cond;
+    int         m_iResourceTaken;
+    CThread::id m_thid;
+};
+
+/// Acquired the shared resource on creation, releases upon destruction.
+class CScopedResourceLock
+{
+public:
+    CScopedResourceLock(CSharedResource& resource)
+        : m_rsrc(resource)
+    {
+        m_rsrc.acquire();
+    }
+
+    ~CScopedResourceLock()
+    {
+        m_rsrc.release();
+    }
+
+private:
+    CSharedResource& m_rsrc;
+};
 
 } // namespace sync
 } // namespace srt