[XrdEc] Ensure parallel execution of Reader::Read is thread-safe.

src/XrdCl/XrdClParallelOperation.hh

@@ -346,6 +346,7 @@ namespace XrdCl
 
         void lift()
         {
+          std::unique_lock<std::mutex> lck( mtx );
           on = false;
           cv.notify_all();
         }

src/XrdEc/XrdEcReader.cc

@@ -506,12 +506,14 @@ namespace XrdEc
       //-------------------------------------------------------------------
       // Make sure we operate on a valid block
       //-------------------------------------------------------------------
+      std::unique_lock<std::mutex> lck( blkmtx );
       if( !block || block->blkid != blkid )
         block = std::make_shared<block_t>( blkid, *this, objcfg );
       //-------------------------------------------------------------------
       // Prepare the callback for reading from single stripe
       //-------------------------------------------------------------------
       auto blk = block;
+      lck.unlock();
       auto callback = [blk, rdctx, rdsize, rdmtx]( const XrdCl::XRootDStatus &st, uint32_t nbrd )
       {
         std::unique_lock<std::mutex> lck( *rdmtx );
@@ -549,7 +551,7 @@ namespace XrdEc
       //-------------------------------------------------------------------
       // Read data from a stripe
       //-------------------------------------------------------------------
-      block_t::read( block, strpid, rdoff, rdsize, usrbuff, callback, timeout );
+      block_t::read( blk, strpid, rdoff, rdsize, usrbuff, callback, timeout );
       //-------------------------------------------------------------------
       // Update absolute offset, read length, and user buffer
       //-------------------------------------------------------------------

src/XrdEc/XrdEcReader.hh

@@ -166,6 +166,7 @@ namespace XrdEc
       urlmap_t                  urlmap;    //> map blknb/strpnb (data chunk) to URL
       missing_t                 missing;   //> set of missing stripes
       std::shared_ptr<block_t>  block;     //> cache for the block we are reading from
+      std::mutex                blkmtx;    //> mutex guarding the block from parallel access
       size_t                    lstblk;    //> last block number
       uint64_t                  filesize;  //> file size (obtained from xattr)
   };