changeset 25740:412b76204e48

8050972: Concurrency problem in PcDesc cache Summary: The entries of the PcDesc cache in nmethods are not declared as volatile, but they are accessed and modified by several threads concurrently. Reviewed-by: kvn, dholmes, dcubed
author mdoerr
date Thu, 17 Jul 2014 10:21:31 +0200
parents 0d9a6751cb1d
children aa6844e3ab10
files hotspot/src/share/vm/code/nmethod.hpp
diffstat 1 files changed, 6 insertions(+), 1 deletions(-) [+]
line wrap: on
line diff
--- a/hotspot/src/share/vm/code/nmethod.hpp	Mon Jul 21 10:25:58 2014 +0200
+++ b/hotspot/src/share/vm/code/nmethod.hpp	Thu Jul 17 10:21:31 2014 +0200
@@ -69,7 +69,12 @@
   friend class VMStructs;
  private:
   enum { cache_size = 4 };
-  PcDesc* _pc_descs[cache_size]; // last cache_size pc_descs found
+  // The array elements MUST be volatile! Several threads may modify
+  // and read from the cache concurrently. find_pc_desc_internal has
+  // returned wrong results. C++ compiler (namely xlC12) may duplicate
+  // C++ field accesses if the elements are not volatile.
+  typedef PcDesc* PcDescPtr;
+  volatile PcDescPtr _pc_descs[cache_size]; // last cache_size pc_descs found
  public:
   PcDescCache() { debug_only(_pc_descs[0] = NULL); }
   void    reset_to(PcDesc* initial_pc_desc);