/*

 * Copyright 1997-2008 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),

    _activated(activated) {

    _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

};