allow concurrency for getpage()

Author: sy-c

src/MemoryPagesPool.cxx

@@ -149,13 +149,22 @@ MemoryPagesPool::~MemoryPagesPool()
 
 void* MemoryPagesPool::getPage()
 {
+  // disable concurrent execution of this function
+  std::unique_lock<std::mutex> lock(pagesAvailableMutexPop);
+
   // update statistics
   poolStats.set((CounterValue)getNumberOfPagesAvailable());
 
   // get a page from fifo, if available
   void* ptr = nullptr;
   pagesAvailable->pop(ptr);
 
+  // udpate buffer state
+  updateBufferState();
+
+  // the following does not need exclusive access, release lock
+  lock.unlock();
+  
   // stats
   if (MemoryPagesPoolStatsEnabled) {
     if (ptr != nullptr) {
@@ -172,9 +181,6 @@ void* MemoryPagesPool::getPage()
     }
   }
 
-  // udpate buffer state
-  updateBufferState();
-
   return ptr;
 }
 

src/MemoryPagesPool.h

@@ -97,6 +97,7 @@ class MemoryPagesPool
 
   std::unique_ptr<AliceO2::Common::Fifo<void*>> pagesAvailable; // a buffer to keep track of individual pages
   std::mutex pagesAvailableMutexPush; // a lock to avoid concurrent push-back of free pages to fifo
+  std::mutex pagesAvailableMutexPop; // a lock to avoid concurrent get free pages from fifo
 
   size_t numberOfPages;                           // number of pages
   size_t pageSize;                                // size of each page, in bytes