--- a/Core/MultiThreading/Semaphore.cpp	Thu Aug 01 11:46:24 2019 +0200
+++ b/Core/MultiThreading/Semaphore.cpp	Thu Aug 01 18:00:22 2019 +0200
@@ -39,10 +39,10 @@
 
 namespace Orthanc
 {
-  Semaphore::Semaphore(unsigned int count) :
-    count_(count)
+  Semaphore::Semaphore(unsigned int availableResources) :
+    availableResources_(availableResources)
   {
-    if (count_ == 0)
+    if (availableResources_ == 0)
     {
       throw OrthancException(ErrorCode_ParameterOutOfRange);
     }
@@ -52,7 +52,7 @@
   {
     boost::mutex::scoped_lock lock(mutex_);
 
-    count_++;
+    availableResources_++;
     condition_.notify_one(); 
   }
 
@@ -60,11 +60,24 @@
   {
     boost::mutex::scoped_lock lock(mutex_);
 
-    while (count_ == 0)
+    while (availableResources_ == 0)
     {
       condition_.wait(lock);
     }
 
-    count_++;
+    availableResources_--;
+  }
+
+  bool Semaphore::TryAcquire()
+  {
+    boost::mutex::scoped_lock lock(mutex_);
+
+    if (availableResources_ == 0)
+    {
+      return false;
+    }
+
+    availableResources_--;
+    return true;
   }
 }

--- a/Core/MultiThreading/Semaphore.h	Thu Aug 01 11:46:24 2019 +0200
+++ b/Core/MultiThreading/Semaphore.h	Thu Aug 01 18:00:22 2019 +0200
@@ -41,7 +41,7 @@
   class Semaphore : public boost::noncopyable
   {
   private:
-    unsigned int count_;
+    unsigned int availableResources_;
     boost::mutex mutex_;
     boost::condition_variable condition_;
     
@@ -49,8 +49,9 @@
 
     void Acquire();
 
+    bool TryAcquire();
   public:
-    explicit Semaphore(unsigned int count);
+    explicit Semaphore(unsigned int availableResources);
 
     class Locker : public boost::noncopyable
     {
@@ -69,5 +70,33 @@
         that_.Release();
       }
     };
+
+    class TryLocker : public boost::noncopyable
+    {
+    private:
+      Semaphore&  that_;
+      bool        isAcquired_;
+
+    public:
+      explicit TryLocker(Semaphore& that) :
+        that_(that)
+      {
+        isAcquired_ = that_.TryAcquire();
+      }
+
+      ~TryLocker()
+      {
+        if (isAcquired_)
+        {
+          that_.Release();
+        }
+      }
+
+      bool IsAcquired() const
+      {
+        return isAcquired_;
+      }
+    };
+
   };
 }