src/share/vm/code/nmethod.hpp
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rev 6728 : 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
@@ -67,11 +67,16 @@
// cache pc descs found in earlier inquiries
class PcDescCache VALUE_OBJ_CLASS_SPEC {
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);
PcDesc* find_pc_desc(int pc_offset, bool approximate);
void add_pc_desc(PcDesc* pc_desc);