Locking pending_transfers_ when canceling transfers.

Author: larshg

examples/protonect/src/transfer_pool.cpp

@@ -115,6 +115,8 @@ void TransferPool::submit(size_t num_parallel_transfers)
 
 void TransferPool::cancel()
 {
+  pending_transfers_lock_.lock();
+  
   for(TransferQueue::iterator it = pending_transfers_.begin(); it != pending_transfers_.end(); ++it)
   {
     int r = libusb_cancel_transfer(*it);
@@ -125,6 +127,8 @@ void TransferPool::cancel()
     }
   }
 
+  pending_transfers_lock_.unlock();
+
   //idle_transfers_.insert(idle_transfers_.end(), pending_transfers_.begin(), pending_transfers_.end());
 }