2008-09-17 Andrew Haley <aph@redhat.com>

        PR libgcj/8995:

        * defineclass.cc (_Jv_ClassReader::handleCodeAttribute):
        Initialize thread_count.
        * include/java-interp.h (_Jv_InterpMethod::thread_count): New
        field.
         (_Jv_InterpMethod::rewrite_insn_mutex): New mutex.
        (_Jv_InterpFrame:: _Jv_InterpFrame): Pass frame_type.
        * interpret.cc
        (ThreadCountAdjuster): New class.
        (_Jv_InterpMethod::thread_count): New field.
        (_Jv_InitInterpreter): Initialize rewrite_insn_mutex.
        Increment and decrement thread_count field in methods.
        * interpret-run.cc (REWRITE_INSN): Check thread_count <= 1.
        (REWRITE_INSN): Likewise.
        Declare a ThreadCountAdjuster.
        * java/lang/reflect/natVMProxy.cc (run_proxy): Initialize frame
        type as frame_proxy.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@140593 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 40 insertions, 27 deletions

diff --git a/libjava/interpret-run.cc b/libjava/interpret-run.cc
index 2934b9b8956..059195360ed 100644
--- a/libjava/interpret-run.cc
+++ b/libjava/interpret-run.cc
@@ -29,6 +29,10 @@ details.  */
   _Jv_InterpFrame frame_desc (meth, thread);
 #endif
 
+#ifdef DIRECT_THREADED
+  ThreadCountAdjuster adj (meth, &frame_desc);
+#endif // DIRECT_THREADED
+
   _Jv_word stack[meth->max_stack];
   _Jv_word *sp = stack;
 
@@ -361,20 +365,29 @@ details.  */
     }									\
   while (0)
 
+// We fail to rewrite a breakpoint if there is another thread
+// currently executing this method.  This is a bug, but there's
+// nothing else we can do that doesn't cause a data race.
 #undef REWRITE_INSN
 #define REWRITE_INSN(INSN,SLOT,VALUE)					\
-  do {									\
-    if (pc[-2].insn == breakpoint_insn->insn)				\
-      {									\
-	using namespace ::gnu::gcj::jvmti;				\
-	jlocation location = meth->insn_index (pc - 2);			\
-	_Jv_RewriteBreakpointInsn (meth->self, location, (pc_t) INSN);	\
-      }									\
-    else								\
-      pc[-2].insn = INSN;						\
+  do									\
+    {									\
+      _Jv_MutexLock (&rewrite_insn_mutex);				\
+      if (meth->thread_count <= 1)					\
+	{								\
+	  if (pc[-2].insn == breakpoint_insn->insn)			\
+	    {								\
+	      using namespace ::gnu::gcj::jvmti;			\
+	      jlocation location = meth->insn_index (pc - 2);		\
+	      _Jv_RewriteBreakpointInsn (meth->self, location, (pc_t) INSN); \
+	    }								\
+	  else								\
+	    pc[-2].insn = INSN;						\
 									\
-    pc[-1].SLOT = VALUE;						\
-  }									\
+	  pc[-1].SLOT = VALUE;						\
+	}								\
+      _Jv_MutexUnlock (&rewrite_insn_mutex);				\
+    }									\
   while (0)
 
 #undef INTERP_REPORT_EXCEPTION
@@ -383,23 +396,23 @@ details.  */
 #undef NEXT_INSN
 #define NEXT_INSN goto *((pc++)->insn)
 
-// REWRITE_INSN does nothing.
-//
 // Rewriting a multi-word instruction in the presence of multiple
-// threads leads to a data race if a thread reads part of an
-// instruction while some other thread is rewriting that instruction.
-// For example, an invokespecial instruction may be rewritten to
-// invokespecial_resolved and its operand changed from an index to a
-// pointer while another thread is executing invokespecial.  This
-// other thread then reads the pointer that is now the operand of
-// invokespecial_resolved and tries to use it as an index.
-//
-// Fixing this requires either spinlocks, a more elaborate data
-// structure, or even per-thread allocated pages.  It's clear from the
-// locking in meth->compile below that the presence of multiple
-// threads was contemplated when this code was written, but the full
-// consequences were not fully appreciated.
-#define REWRITE_INSN(INSN,SLOT,VALUE)
+// threads is a data race if a thread reads part of an instruction
+// while some other thread is rewriting that instruction.  We detect
+// more than one thread executing a method and don't rewrite the
+// instruction.  A thread entering a method blocks on
+// rewrite_insn_mutex until the write is complete.
+#define REWRITE_INSN(INSN,SLOT,VALUE)		\
+  do {						\
+    _Jv_MutexLock (&rewrite_insn_mutex);	\
+    if (meth->thread_count <= 1)		\
+      {						\
+	pc[-2].insn = INSN;			\
+	pc[-1].SLOT = VALUE;			\
+      }						\
+    _Jv_MutexUnlock (&rewrite_insn_mutex);	\
+  }						\
+  while (0)
 
 #undef INTERP_REPORT_EXCEPTION
 #define INTERP_REPORT_EXCEPTION(Jthrowable) /* not needed when not debugging */