--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/share/vm/memory/gcLocker.hpp	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,285 @@
+/*
+ * Copyright 1997-2007 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+// The direct lock/unlock calls do not force a collection if an unlock
+// decrements the count to zero. Avoid calling these if at all possible.
+
+class GC_locker: public AllStatic {
+ private:
+  static volatile jint _jni_lock_count;  // number of jni active instances
+  static volatile jint _lock_count;      // number of other active instances
+  static volatile bool _needs_gc;        // heap is filling, we need a GC
+                                         // note: bool is typedef'd as jint
+  static volatile bool _doing_gc;        // unlock_critical() is doing a GC
+
+  // Accessors
+  static bool is_jni_active() {
+    return _jni_lock_count > 0;
+  }
+
+  static void set_needs_gc() {
+    assert(SafepointSynchronize::is_at_safepoint(),
+      "needs_gc is only set at a safepoint");
+    _needs_gc = true;
+  }
+
+  static void clear_needs_gc() {
+    assert_lock_strong(JNICritical_lock);
+    _needs_gc = false;
+  }
+
+  static void jni_lock() {
+    Atomic::inc(&_jni_lock_count);
+    CHECK_UNHANDLED_OOPS_ONLY(
+      if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count++; })
+    assert(Universe::heap() == NULL || !Universe::heap()->is_gc_active(),
+           "locking failed");
+  }
+
+  static void jni_unlock() {
+    Atomic::dec(&_jni_lock_count);
+    CHECK_UNHANDLED_OOPS_ONLY(
+      if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count--; })
+  }
+
+  static void jni_lock_slow();
+  static void jni_unlock_slow();
+
+ public:
+  // Accessors
+  static bool is_active();
+  static bool needs_gc()       { return _needs_gc;                        }
+  // Shorthand
+  static bool is_active_and_needs_gc() { return is_active() && needs_gc();}
+
+  // Calls set_needs_gc() if is_active() is true. Returns is_active().
+  static bool check_active_before_gc();
+
+  // Stalls the caller (who should not be in a jni critical section)
+  // until needs_gc() clears. Note however that needs_gc() may be
+  // set at a subsequent safepoint and/or cleared under the
+  // JNICritical_lock, so the caller may not safely assert upon
+  // return from this method that "!needs_gc()" since that is
+  // not a stable predicate.
+  static void stall_until_clear();
+
+  // Non-structured GC locking: currently needed for JNI. Use with care!
+  static void lock();
+  static void unlock();
+
+  // The following two methods are used for JNI critical regions.
+  // If we find that we failed to perform a GC because the GC_locker
+  // was active, arrange for one as soon as possible by allowing
+  // all threads in critical regions to complete, but not allowing
+  // other critical regions to be entered. The reasons for that are:
+  // 1) a GC request won't be starved by overlapping JNI critical
+  //    region activities, which can cause unnecessary OutOfMemory errors.
+  // 2) even if allocation requests can still be satisfied before GC locker
+  //    becomes inactive, for example, in tenured generation possibly with
+  //    heap expansion, those allocations can trigger lots of safepointing
+  //    attempts (ineffective GC attempts) and require Heap_lock which
+  //    slow down allocations tremendously.
+  //
+  // Note that critical regions can be nested in a single thread, so
+  // we must allow threads already in critical regions to continue.
+  //
+  // JNI critical regions are the only participants in this scheme
+  // because they are, by spec, well bounded while in a critical region.
+  //
+  // Each of the following two method is split into a fast path and a slow
+  // path. JNICritical_lock is only grabbed in the slow path.
+  // _needs_gc is initially false and every java thread will go
+  // through the fast path (which does the same thing as the slow path
+  // when _needs_gc is false). When GC happens at a safepoint,
+  // GC_locker::is_active() is checked. Since there is no safepoint in the
+  // fast path of lock_critical() and unlock_critical(), there is no race
+  // condition between the fast path and GC. After _needs_gc is set at a
+  // safepoint, every thread will go through the slow path after the safepoint.
+  // Since after a safepoint, each of the following two methods is either
+  // entered from the method entry and falls into the slow path, or is
+  // resumed from the safepoints in the method, which only exist in the slow
+  // path. So when _needs_gc is set, the slow path is always taken, till
+  // _needs_gc is cleared.
+  static void lock_critical(JavaThread* thread);
+  static void unlock_critical(JavaThread* thread);
+};
+
+
+// A No_GC_Verifier object can be placed in methods where one assumes that
+// no garbage collection will occur. The destructor will verify this property
+// unless the constructor is called with argument false (not verifygc).
+//
+// The check will only be done in debug mode and if verifygc true.
+
+class No_GC_Verifier: public StackObj {
+ friend class Pause_No_GC_Verifier;
+
+ protected:
+  bool _verifygc;
+  unsigned int _old_invocations;
+
+ public:
+#ifdef ASSERT
+  No_GC_Verifier(bool verifygc = true);
+  ~No_GC_Verifier();
+#else
+  No_GC_Verifier(bool verifygc = true) {}
+  ~No_GC_Verifier() {}
+#endif
+};
+
+// A Pause_No_GC_Verifier is used to temporarily pause the behavior
+// of a No_GC_Verifier object. If we are not in debug mode or if the
+// No_GC_Verifier object has a _verifygc value of false, then there
+// is nothing to do.
+
+class Pause_No_GC_Verifier: public StackObj {
+ private:
+  No_GC_Verifier * _ngcv;
+
+ public:
+#ifdef ASSERT
+  Pause_No_GC_Verifier(No_GC_Verifier * ngcv);
+  ~Pause_No_GC_Verifier();
+#else
+  Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {}
+  ~Pause_No_GC_Verifier() {}
+#endif
+};
+
+
+// A No_Safepoint_Verifier object will throw an assertion failure if
+// the current thread passes a possible safepoint while this object is
+// instantiated. A safepoint, will either be: an oop allocation, blocking
+// on a Mutex or JavaLock, or executing a VM operation.
+//
+// If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
+//
+class No_Safepoint_Verifier : public No_GC_Verifier {
+ friend class Pause_No_Safepoint_Verifier;
+
+ private:
+  bool _activated;
+  Thread *_thread;
+ public:
+#ifdef ASSERT
+  No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) : No_GC_Verifier(verifygc) {
+    _thread = Thread::current();
+    if (_activated) {
+      _thread->_allow_allocation_count++;
+      _thread->_allow_safepoint_count++;
+    }
+  }
+
+  ~No_Safepoint_Verifier() {
+    if (_activated) {
+      _thread->_allow_allocation_count--;
+      _thread->_allow_safepoint_count--;
+    }
+  }
+#else
+  No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){}
+  ~No_Safepoint_Verifier() {}
+#endif
+};
+
+// A Pause_No_Safepoint_Verifier is used to temporarily pause the
+// behavior of a No_Safepoint_Verifier object. If we are not in debug
+// mode then there is nothing to do. If the No_Safepoint_Verifier
+// object has an _activated value of false, then there is nothing to
+// do for safepoint and allocation checking, but there may still be
+// something to do for the underlying No_GC_Verifier object.
+
+class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier {
+ private:
+  No_Safepoint_Verifier * _nsv;
+
+ public:
+#ifdef ASSERT
+  Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
+    : Pause_No_GC_Verifier(nsv) {
+
+    _nsv = nsv;
+    if (_nsv->_activated) {
+      _nsv->_thread->_allow_allocation_count--;
+      _nsv->_thread->_allow_safepoint_count--;
+    }
+  }
+
+  ~Pause_No_Safepoint_Verifier() {
+    if (_nsv->_activated) {
+      _nsv->_thread->_allow_allocation_count++;
+      _nsv->_thread->_allow_safepoint_count++;
+    }
+  }
+#else
+  Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
+    : Pause_No_GC_Verifier(nsv) {}
+  ~Pause_No_Safepoint_Verifier() {}
+#endif
+};
+
+// JRT_LEAF currently can be called from either _thread_in_Java or
+// _thread_in_native mode. In _thread_in_native, it is ok
+// for another thread to trigger GC. The rest of the JRT_LEAF
+// rules apply.
+class JRT_Leaf_Verifier : public No_Safepoint_Verifier {
+  static bool should_verify_GC();
+ public:
+#ifdef ASSERT
+  JRT_Leaf_Verifier();
+  ~JRT_Leaf_Verifier();
+#else
+  JRT_Leaf_Verifier() {}
+  ~JRT_Leaf_Verifier() {}
+#endif
+};
+
+// A No_Alloc_Verifier object can be placed in methods where one assumes that
+// no allocation will occur. The destructor will verify this property
+// unless the constructor is called with argument false (not activated).
+//
+// The check will only be done in debug mode and if activated.
+// Note: this only makes sense at safepoints (otherwise, other threads may
+// allocate concurrently.)
+
+class No_Alloc_Verifier : public StackObj {
+ private:
+  bool  _activated;
+
+ public:
+#ifdef ASSERT
+  No_Alloc_Verifier(bool activated = true) {
+    _activated = activated;
+    if (_activated) Thread::current()->_allow_allocation_count++;
+  }
+
+  ~No_Alloc_Verifier() {
+    if (_activated) Thread::current()->_allow_allocation_count--;
+  }
+#else
+  No_Alloc_Verifier(bool activated = true) {}
+  ~No_Alloc_Verifier() {}
+#endif
+};