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 /*

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  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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  * 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 #ifndef SHARE_VM_MEMORY_GCLOCKER_HPP

 #define SHARE_VM_MEMORY_GCLOCKER_HPP

 #include "gc_interface/collectedHeap.hpp"

 #include "memory/genCollectedHeap.hpp"

 #include "memory/universe.hpp"

 #include "oops/oop.hpp"

 #include "runtime/thread.inline.hpp"

 #ifdef TARGET_OS_FAMILY_linux

 # include "os_linux.inline.hpp"

 #endif

 #ifdef TARGET_OS_FAMILY_solaris

 # include "os_solaris.inline.hpp"

 #endif

 #ifdef TARGET_OS_FAMILY_windows

 # include "os_windows.inline.hpp"

 #endif

 #ifdef TARGET_OS_FAMILY_bsd

 # include "os_bsd.inline.hpp"

 #endif

 // 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:

   // The _jni_lock_count keeps track of the number of threads that are

   // currently in a critical region.  It's only kept up to date when

   // _needs_gc is true.  The current value is computed during

   // safepointing and decremented during the slow path of GC_locker

   // unlocking.

   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

 #ifdef ASSERT

   // This lock count is updated for all operations and is used to

   // validate the jni_lock_count that is computed during safepoints.

   static volatile jint _debug_jni_lock_count;

 #endif

   // Accessors

   static bool is_jni_active() {

     assert(_needs_gc, "only valid when _needs_gc is set");

     return _jni_lock_count > 0;

   }

   // At a safepoint, visit all threads and count the number of active

   // critical sections.  This is used to ensure that all active

   // critical sections are exited before a new one is started.

   static void verify_critical_count() NOT_DEBUG_RETURN;

   static void jni_lock(JavaThread* thread);

   static void jni_unlock(JavaThread* thread);

   static bool is_active_internal() {

     verify_critical_count();

     return _lock_count > 0 || _jni_lock_count > 0;

   }

  public:

   // Accessors

   static bool is_active() {

     assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");

     return is_active_internal();

   }

   static bool needs_gc()       { return _needs_gc;                        }

   // Shorthand

   static bool is_active_and_needs_gc() {

     // Use is_active_internal since _needs_gc can change from true to

     // false outside of a safepoint, triggering the assert in

     // is_active.

     return needs_gc() && is_active_internal();

   }

   // In debug mode track the locking state at all times

   static void increment_debug_jni_lock_count() {

 #ifdef ASSERT

     assert(_debug_jni_lock_count >= 0, "bad value");

     Atomic::inc(&_debug_jni_lock_count);

 #endif

   }

   static void decrement_debug_jni_lock_count() {

 #ifdef ASSERT

     assert(_debug_jni_lock_count > 0, "bad value");

     Atomic::dec(&_debug_jni_lock_count);

 #endif

   }

   // Set the current lock count

   static void set_jni_lock_count(int count) {

     _jni_lock_count = count;

     verify_critical_count();

   }

   // Sets _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 simply increments or decrements the

   // current thread's critical count.  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);

   static address needs_gc_address() { return (address) &_needs_gc; }

 };

 // 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

 };

 // A SkipGCALot object is used to elide the usual effect of gc-a-lot

 // over a section of execution by a thread. Currently, it's used only to

 // prevent re-entrant calls to GC.

 class SkipGCALot : public StackObj {

   private:

    bool _saved;

    Thread* _t;

   public:

 #ifdef ASSERT

     SkipGCALot(Thread* t) : _t(t) {

       _saved = _t->skip_gcalot();

       _t->set_skip_gcalot(true);

     }

     ~SkipGCALot() {

       assert(_t->skip_gcalot(), "Save-restore protocol invariant");

       _t->set_skip_gcalot(_saved);

     }

 #else

     SkipGCALot(Thread* t) { }

     ~SkipGCALot() { }

 #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

 };

 #endif // SHARE_VM_MEMORY_GCLOCKER_HPP