duke@435: /*
xdono@1279:  * Copyright 1997-2009 Sun Microsystems, Inc.  All Rights Reserved.
duke@435:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
duke@435:  *
duke@435:  * This code is free software; you can redistribute it and/or modify it
duke@435:  * under the terms of the GNU General Public License version 2 only, as
duke@435:  * published by the Free Software Foundation.
duke@435:  *
duke@435:  * This code is distributed in the hope that it will be useful, but WITHOUT
duke@435:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
duke@435:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
duke@435:  * version 2 for more details (a copy is included in the LICENSE file that
duke@435:  * accompanied this code).
duke@435:  *
duke@435:  * You should have received a copy of the GNU General Public License version
duke@435:  * 2 along with this work; if not, write to the Free Software Foundation,
duke@435:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
duke@435:  *
duke@435:  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
duke@435:  * CA 95054 USA or visit www.sun.com if you need additional information or
duke@435:  * have any questions.
duke@435:  *
duke@435:  */
duke@435: 
duke@435: // The direct lock/unlock calls do not force a collection if an unlock
duke@435: // decrements the count to zero. Avoid calling these if at all possible.
duke@435: 
duke@435: class GC_locker: public AllStatic {
duke@435:  private:
duke@435:   static volatile jint _jni_lock_count;  // number of jni active instances
duke@435:   static volatile jint _lock_count;      // number of other active instances
duke@435:   static volatile bool _needs_gc;        // heap is filling, we need a GC
duke@435:                                          // note: bool is typedef'd as jint
duke@435:   static volatile bool _doing_gc;        // unlock_critical() is doing a GC
duke@435: 
duke@435:   // Accessors
duke@435:   static bool is_jni_active() {
duke@435:     return _jni_lock_count > 0;
duke@435:   }
duke@435: 
duke@435:   static void set_needs_gc() {
duke@435:     assert(SafepointSynchronize::is_at_safepoint(),
duke@435:       "needs_gc is only set at a safepoint");
duke@435:     _needs_gc = true;
duke@435:   }
duke@435: 
duke@435:   static void clear_needs_gc() {
duke@435:     assert_lock_strong(JNICritical_lock);
duke@435:     _needs_gc = false;
duke@435:   }
duke@435: 
duke@435:   static void jni_lock() {
duke@435:     Atomic::inc(&_jni_lock_count);
duke@435:     CHECK_UNHANDLED_OOPS_ONLY(
duke@435:       if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count++; })
duke@435:     assert(Universe::heap() == NULL || !Universe::heap()->is_gc_active(),
duke@435:            "locking failed");
duke@435:   }
duke@435: 
duke@435:   static void jni_unlock() {
duke@435:     Atomic::dec(&_jni_lock_count);
duke@435:     CHECK_UNHANDLED_OOPS_ONLY(
duke@435:       if (CheckUnhandledOops) { Thread::current()->_gc_locked_out_count--; })
duke@435:   }
duke@435: 
duke@435:   static void jni_lock_slow();
duke@435:   static void jni_unlock_slow();
duke@435: 
duke@435:  public:
duke@435:   // Accessors
duke@435:   static bool is_active();
duke@435:   static bool needs_gc()       { return _needs_gc;                        }
duke@435:   // Shorthand
duke@435:   static bool is_active_and_needs_gc() { return is_active() && needs_gc();}
duke@435: 
duke@435:   // Calls set_needs_gc() if is_active() is true. Returns is_active().
duke@435:   static bool check_active_before_gc();
duke@435: 
duke@435:   // Stalls the caller (who should not be in a jni critical section)
duke@435:   // until needs_gc() clears. Note however that needs_gc() may be
duke@435:   // set at a subsequent safepoint and/or cleared under the
duke@435:   // JNICritical_lock, so the caller may not safely assert upon
duke@435:   // return from this method that "!needs_gc()" since that is
duke@435:   // not a stable predicate.
duke@435:   static void stall_until_clear();
duke@435: 
duke@435:   // Non-structured GC locking: currently needed for JNI. Use with care!
duke@435:   static void lock();
duke@435:   static void unlock();
duke@435: 
duke@435:   // The following two methods are used for JNI critical regions.
duke@435:   // If we find that we failed to perform a GC because the GC_locker
duke@435:   // was active, arrange for one as soon as possible by allowing
duke@435:   // all threads in critical regions to complete, but not allowing
duke@435:   // other critical regions to be entered. The reasons for that are:
duke@435:   // 1) a GC request won't be starved by overlapping JNI critical
duke@435:   //    region activities, which can cause unnecessary OutOfMemory errors.
duke@435:   // 2) even if allocation requests can still be satisfied before GC locker
duke@435:   //    becomes inactive, for example, in tenured generation possibly with
duke@435:   //    heap expansion, those allocations can trigger lots of safepointing
duke@435:   //    attempts (ineffective GC attempts) and require Heap_lock which
duke@435:   //    slow down allocations tremendously.
duke@435:   //
duke@435:   // Note that critical regions can be nested in a single thread, so
duke@435:   // we must allow threads already in critical regions to continue.
duke@435:   //
duke@435:   // JNI critical regions are the only participants in this scheme
duke@435:   // because they are, by spec, well bounded while in a critical region.
duke@435:   //
duke@435:   // Each of the following two method is split into a fast path and a slow
duke@435:   // path. JNICritical_lock is only grabbed in the slow path.
duke@435:   // _needs_gc is initially false and every java thread will go
duke@435:   // through the fast path (which does the same thing as the slow path
duke@435:   // when _needs_gc is false). When GC happens at a safepoint,
duke@435:   // GC_locker::is_active() is checked. Since there is no safepoint in the
duke@435:   // fast path of lock_critical() and unlock_critical(), there is no race
duke@435:   // condition between the fast path and GC. After _needs_gc is set at a
duke@435:   // safepoint, every thread will go through the slow path after the safepoint.
duke@435:   // Since after a safepoint, each of the following two methods is either
duke@435:   // entered from the method entry and falls into the slow path, or is
duke@435:   // resumed from the safepoints in the method, which only exist in the slow
duke@435:   // path. So when _needs_gc is set, the slow path is always taken, till
duke@435:   // _needs_gc is cleared.
duke@435:   static void lock_critical(JavaThread* thread);
duke@435:   static void unlock_critical(JavaThread* thread);
duke@435: };
duke@435: 
duke@435: 
duke@435: // A No_GC_Verifier object can be placed in methods where one assumes that
duke@435: // no garbage collection will occur. The destructor will verify this property
duke@435: // unless the constructor is called with argument false (not verifygc).
duke@435: //
duke@435: // The check will only be done in debug mode and if verifygc true.
duke@435: 
duke@435: class No_GC_Verifier: public StackObj {
duke@435:  friend class Pause_No_GC_Verifier;
duke@435: 
duke@435:  protected:
duke@435:   bool _verifygc;
duke@435:   unsigned int _old_invocations;
duke@435: 
duke@435:  public:
duke@435: #ifdef ASSERT
duke@435:   No_GC_Verifier(bool verifygc = true);
duke@435:   ~No_GC_Verifier();
duke@435: #else
duke@435:   No_GC_Verifier(bool verifygc = true) {}
duke@435:   ~No_GC_Verifier() {}
duke@435: #endif
duke@435: };
duke@435: 
duke@435: // A Pause_No_GC_Verifier is used to temporarily pause the behavior
duke@435: // of a No_GC_Verifier object. If we are not in debug mode or if the
duke@435: // No_GC_Verifier object has a _verifygc value of false, then there
duke@435: // is nothing to do.
duke@435: 
duke@435: class Pause_No_GC_Verifier: public StackObj {
duke@435:  private:
duke@435:   No_GC_Verifier * _ngcv;
duke@435: 
duke@435:  public:
duke@435: #ifdef ASSERT
duke@435:   Pause_No_GC_Verifier(No_GC_Verifier * ngcv);
duke@435:   ~Pause_No_GC_Verifier();
duke@435: #else
duke@435:   Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {}
duke@435:   ~Pause_No_GC_Verifier() {}
duke@435: #endif
duke@435: };
duke@435: 
duke@435: 
duke@435: // A No_Safepoint_Verifier object will throw an assertion failure if
duke@435: // the current thread passes a possible safepoint while this object is
duke@435: // instantiated. A safepoint, will either be: an oop allocation, blocking
duke@435: // on a Mutex or JavaLock, or executing a VM operation.
duke@435: //
duke@435: // If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
duke@435: //
duke@435: class No_Safepoint_Verifier : public No_GC_Verifier {
duke@435:  friend class Pause_No_Safepoint_Verifier;
duke@435: 
duke@435:  private:
duke@435:   bool _activated;
duke@435:   Thread *_thread;
duke@435:  public:
duke@435: #ifdef ASSERT
never@533:   No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) :
never@533:     No_GC_Verifier(verifygc),
never@533:     _activated(activated) {
duke@435:     _thread = Thread::current();
duke@435:     if (_activated) {
duke@435:       _thread->_allow_allocation_count++;
duke@435:       _thread->_allow_safepoint_count++;
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   ~No_Safepoint_Verifier() {
duke@435:     if (_activated) {
duke@435:       _thread->_allow_allocation_count--;
duke@435:       _thread->_allow_safepoint_count--;
duke@435:     }
duke@435:   }
duke@435: #else
duke@435:   No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){}
duke@435:   ~No_Safepoint_Verifier() {}
duke@435: #endif
duke@435: };
duke@435: 
duke@435: // A Pause_No_Safepoint_Verifier is used to temporarily pause the
duke@435: // behavior of a No_Safepoint_Verifier object. If we are not in debug
duke@435: // mode then there is nothing to do. If the No_Safepoint_Verifier
duke@435: // object has an _activated value of false, then there is nothing to
duke@435: // do for safepoint and allocation checking, but there may still be
duke@435: // something to do for the underlying No_GC_Verifier object.
duke@435: 
duke@435: class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier {
duke@435:  private:
duke@435:   No_Safepoint_Verifier * _nsv;
duke@435: 
duke@435:  public:
duke@435: #ifdef ASSERT
duke@435:   Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
duke@435:     : Pause_No_GC_Verifier(nsv) {
duke@435: 
duke@435:     _nsv = nsv;
duke@435:     if (_nsv->_activated) {
duke@435:       _nsv->_thread->_allow_allocation_count--;
duke@435:       _nsv->_thread->_allow_safepoint_count--;
duke@435:     }
duke@435:   }
duke@435: 
duke@435:   ~Pause_No_Safepoint_Verifier() {
duke@435:     if (_nsv->_activated) {
duke@435:       _nsv->_thread->_allow_allocation_count++;
duke@435:       _nsv->_thread->_allow_safepoint_count++;
duke@435:     }
duke@435:   }
duke@435: #else
duke@435:   Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
duke@435:     : Pause_No_GC_Verifier(nsv) {}
duke@435:   ~Pause_No_Safepoint_Verifier() {}
duke@435: #endif
duke@435: };
duke@435: 
ysr@1241: // A SkipGCALot object is used to elide the usual effect of gc-a-lot
ysr@1241: // over a section of execution by a thread. Currently, it's used only to
ysr@1241: // prevent re-entrant calls to GC.
ysr@1241: class SkipGCALot : public StackObj {
ysr@1241:   private:
ysr@1241:    bool _saved;
ysr@1241:    Thread* _t;
ysr@1241: 
ysr@1241:   public:
ysr@1241: #ifdef ASSERT
ysr@1241:     SkipGCALot(Thread* t) : _t(t) {
ysr@1241:       _saved = _t->skip_gcalot();
ysr@1241:       _t->set_skip_gcalot(true);
ysr@1241:     }
ysr@1241: 
ysr@1241:     ~SkipGCALot() {
ysr@1241:       assert(_t->skip_gcalot(), "Save-restore protocol invariant");
ysr@1241:       _t->set_skip_gcalot(_saved);
ysr@1241:     }
ysr@1241: #else
ysr@1241:     SkipGCALot(Thread* t) { }
ysr@1241:     ~SkipGCALot() { }
ysr@1241: #endif
ysr@1241: };
ysr@1241: 
duke@435: // JRT_LEAF currently can be called from either _thread_in_Java or
duke@435: // _thread_in_native mode. In _thread_in_native, it is ok
duke@435: // for another thread to trigger GC. The rest of the JRT_LEAF
duke@435: // rules apply.
duke@435: class JRT_Leaf_Verifier : public No_Safepoint_Verifier {
duke@435:   static bool should_verify_GC();
duke@435:  public:
duke@435: #ifdef ASSERT
duke@435:   JRT_Leaf_Verifier();
duke@435:   ~JRT_Leaf_Verifier();
duke@435: #else
duke@435:   JRT_Leaf_Verifier() {}
duke@435:   ~JRT_Leaf_Verifier() {}
duke@435: #endif
duke@435: };
duke@435: 
duke@435: // A No_Alloc_Verifier object can be placed in methods where one assumes that
duke@435: // no allocation will occur. The destructor will verify this property
duke@435: // unless the constructor is called with argument false (not activated).
duke@435: //
duke@435: // The check will only be done in debug mode and if activated.
duke@435: // Note: this only makes sense at safepoints (otherwise, other threads may
duke@435: // allocate concurrently.)
duke@435: 
duke@435: class No_Alloc_Verifier : public StackObj {
duke@435:  private:
duke@435:   bool  _activated;
duke@435: 
duke@435:  public:
duke@435: #ifdef ASSERT
duke@435:   No_Alloc_Verifier(bool activated = true) {
duke@435:     _activated = activated;
duke@435:     if (_activated) Thread::current()->_allow_allocation_count++;
duke@435:   }
duke@435: 
duke@435:   ~No_Alloc_Verifier() {
duke@435:     if (_activated) Thread::current()->_allow_allocation_count--;
duke@435:   }
duke@435: #else
duke@435:   No_Alloc_Verifier(bool activated = true) {}
duke@435:   ~No_Alloc_Verifier() {}
duke@435: #endif
duke@435: };