src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp

@@ -38,11 +38,11 @@
 #endif
 
 class ConcurrentMarkSweepGeneration;
 class CMSCollector;
 
-// The Concurrent Mark Sweep GC Thread (could be several in the future).
+// The Concurrent Mark Sweep GC Thread
 class ConcurrentMarkSweepThread: public ConcurrentGCThread {
   friend class VMStructs;
   friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship
   friend class CMSCollector;
  public:

@@ -53,12 +53,10 @@
   static CMSCollector*                  _collector;
   static SurrogateLockerThread*         _slt;
   static SurrogateLockerThread::SLT_msg_type _sltBuffer;
   static Monitor*                       _sltMonitor;
 
-  ConcurrentMarkSweepThread*            _next;
-
   static bool _should_terminate;
 
   enum CMS_flag_type {
     CMS_nil             = NoBits,
     CMS_cms_wants_token = nth_bit(0),

@@ -82,11 +80,11 @@
   static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing
 
   // Tracing messages, enabled by CMSTraceThreadState.
   static inline void trace_state(const char* desc);
 
-  static volatile bool _icms_enabled;   // iCMS enabled?
+  static volatile int _icms_disabled;   // a counter to track #iCMS disable & enable
   static volatile bool _should_run;     // iCMS may run
   static volatile bool _should_stop;    // iCMS should stop
 
   // debugging
   void verify_ok_to_terminate() const PRODUCT_RETURN;

@@ -212,14 +210,29 @@
   static void stop_icms();  // request thread to stop working
   void icms_wait();         // if asked to stop, wait until notified to start
 
   // Incremental mode is enabled globally by the flag CMSIncrementalMode.  It
   // must also be enabled/disabled dynamically to allow foreground collections.
-  static inline void enable_icms()              { _icms_enabled = true; }
-  static inline void disable_icms()             { _icms_enabled = false; }
-  static inline void set_icms_enabled(bool val) { _icms_enabled = val; }
-  static inline bool icms_enabled()             { return _icms_enabled; }
+#define ICMS_ENABLING_ASSERT                                                      \
+          assert((CMSIncrementalMode  && _icms_disabled >= 0) ||                  \
+                 (!CMSIncrementalMode && _icms_disabled <= 0), "Error")
+
+  static inline void enable_icms() {
+    ICMS_ENABLING_ASSERT;
+    Atomic::dec(&_icms_disabled);
+  }
+  static inline void disable_icms() {
+   ICMS_ENABLING_ASSERT;
+   Atomic::inc(&_icms_disabled);
+  }
+  static inline bool icms_is_disabled() {
+   ICMS_ENABLING_ASSERT;
+   return _icms_disabled > 0;
+  }
+  static inline bool icms_is_enabled() {
+   return !icms_is_disabled();
+  }
 };
 
 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
   if (CMSTraceThreadState) {
     char buf[128];