Patch: FYI: Fix PR 7587 - interpreter thread safety

[Bryce McKinlay <mckinlay at redhat dot com>]

Currently the interpreter can crash if a method is "compiled" 
simultaniously by two different threads. This was occuring quite 
frequently running GCTest on my machine. This patch fixes it by 
introducing a global lock around _Jv_InterpMethod::compile(). Ideally 
we'd have a more fine-grained lock, however I don't think its safe to 
use the class lock because user code might hold it and there would be a 
potential for deadlock.

I'm checking this in.

Regards

Bryce

2004-07-13  Bryce McKinlay  <mckinlay@redhat.com>

	PR libgcj/7587
	* interpret.cc (compile_mutex): New.
	(_Jv_InitInterpreter): New. Initialize compile_mutex.
	(run): Lock compile_mutex before calling compile() if compilation is
	required.
	* prims.cc (_Jv_CreateJavaVM): Call _Jv_InitInterpreter().
	* include/java-interp.h (_Jv_InitInterpreter): Declare.

Index: prims.cc
===================================================================
RCS file: /cvs/gcc/gcc/libjava/prims.cc,v
retrieving revision 1.91
diff -u -r1.91 prims.cc
--- prims.cc	11 Jul 2004 21:19:46 -0000	1.91
+++ prims.cc	13 Jul 2004 21:01:47 -0000
@@ -25,6 +25,7 @@
 #include <jvm.h>
 #include <java-signal.h>
 #include <java-threads.h>
+#include <java-interp.h>
 
 #ifdef ENABLE_JVMPI
 #include <jvmpi.h>
@@ -953,6 +954,10 @@
   _Jv_InitThreads ();
   _Jv_InitGC ();
   _Jv_InitializeSyncMutex ();
+  
+#ifdef INTERPRETER
+  _Jv_InitInterpreter ();
+#endif  
 
 #ifdef HANDLE_SEGV
   INIT_SEGV;
Index: interpret.cc
===================================================================
RCS file: /cvs/gcc/gcc/libjava/interpret.cc,v
retrieving revision 1.43
diff -u -r1.43 interpret.cc
--- interpret.cc	13 Jul 2004 01:04:46 -0000	1.43
+++ interpret.cc	13 Jul 2004 21:01:48 -0000
@@ -54,6 +54,21 @@
   __attribute__ ((__noreturn__));
 #endif
 
+#ifdef DIRECT_THREADED
+// Lock to ensure that methods are not compiled concurrently.
+// We could use a finer-grained lock here, however it is not safe to use
+// the Class monitor as user code in another thread could hold it.
+static _Jv_Mutex_t compile_mutex;
+
+void
+_Jv_InitInterpreter()
+{
+  _Jv_MutexInit (&compile_mutex);
+}
+#else
+void _Jv_InitInterpreter() {}
+#endif
+
 extern "C" double __ieee754_fmod (double,double);
 
 // This represents a single slot in the "compiled" form of the
@@ -1032,9 +1047,14 @@
 #define PCVAL(unionval) unionval.p
 #define AMPAMP(label) &&label
 
-  // Compile if we must.
+  // Compile if we must. NOTE: Double-check locking.
   if (prepared == NULL)
-    compile (insn_target);
+    {
+      _Jv_MutexLock (&compile_mutex);
+      if (prepared == NULL)
+	compile (insn_target);
+      _Jv_MutexUnlock (&compile_mutex);
+    }
   pc = (insn_slot *) prepared;
 
 #else
Index: include/java-interp.h
===================================================================
RCS file: /cvs/gcc/gcc/libjava/include/java-interp.h,v
retrieving revision 1.24
diff -u -r1.24 java-interp.h
--- include/java-interp.h	20 Apr 2004 01:38:45 -0000	1.24
+++ include/java-interp.h	13 Jul 2004 21:01:48 -0000
@@ -35,6 +35,7 @@
 
 struct _Jv_ResolvedMethod;
 
+void _Jv_InitInterpreter ();
 void _Jv_DefineClass (jclass, jbyteArray, jint, jint);
 
 void _Jv_InitField (jobject, jclass, int);