diff data/fft/FFTDataServer.cpp @ 548:1469caaa8e67

* Finer locking in fft caches; fix displayed bin ranges in spectrogram

--- a/data/fft/FFTDataServer.cpp	Wed Feb 04 20:39:11 2009 +0000
+++ b/data/fft/FFTDataServer.cpp	Thu Feb 05 12:05:28 2009 +0000
@@ -738,13 +738,25 @@
 bool
 FFTDataServer::makeCache(int c)
 {
-    QWriteLocker locker(&m_cacheVectorLock);
+    // Creating the cache could take a significant amount of time.  We
+    // don't want to block readers on m_cacheVectorLock while this is
+    // happening, but we do want to block any further calls to
+    // makeCache.  So we use this lock solely to serialise this
+    // particular function -- it isn't used anywhere else.
 
+    QMutexLocker locker(&m_cacheCreationMutex);
+
+    m_cacheVectorLock.lockForRead();
     if (m_caches[c]) {
         // someone else must have created the cache between our
-        // testing for it and taking the write lock
+        // testing for it and taking the mutex
+        m_cacheVectorLock.unlock();
         return true;
     }
+    m_cacheVectorLock.unlock();
+
+    // Now m_cacheCreationMutex is held, but m_cacheVectorLock is not
+    // -- readers can proceed, but callers to this function will block
 
     CacheBlock *cb = new CacheBlock;
 
@@ -811,8 +823,12 @@
         }
     }
 
+    m_cacheVectorLock.lockForWrite();
+
     m_caches[c] = cb;
 
+    m_cacheVectorLock.unlock();
+
     return success;
 }