aoqi@0: /*
aoqi@0:  * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
aoqi@0:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
aoqi@0:  *
aoqi@0:  * This code is free software; you can redistribute it and/or modify it
aoqi@0:  * under the terms of the GNU General Public License version 2 only, as
aoqi@0:  * published by the Free Software Foundation.
aoqi@0:  *
aoqi@0:  * This code is distributed in the hope that it will be useful, but WITHOUT
aoqi@0:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
aoqi@0:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
aoqi@0:  * version 2 for more details (a copy is included in the LICENSE file that
aoqi@0:  * accompanied this code).
aoqi@0:  *
aoqi@0:  * You should have received a copy of the GNU General Public License version
aoqi@0:  * 2 along with this work; if not, write to the Free Software Foundation,
aoqi@0:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
aoqi@0:  *
aoqi@0:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
aoqi@0:  * or visit www.oracle.com if you need additional information or have any
aoqi@0:  * questions.
aoqi@0:  *
aoqi@0:  */
aoqi@0: 
aoqi@0: #ifndef SHARE_VM_MEMORY_GCLOCKER_HPP
aoqi@0: #define SHARE_VM_MEMORY_GCLOCKER_HPP
aoqi@0: 
aoqi@0: #include "gc_interface/collectedHeap.hpp"
aoqi@0: #include "memory/genCollectedHeap.hpp"
aoqi@0: #include "memory/universe.hpp"
aoqi@0: #include "oops/oop.hpp"
aoqi@0: #include "runtime/thread.inline.hpp"
aoqi@0: #ifdef TARGET_OS_FAMILY_linux
aoqi@0: # include "os_linux.inline.hpp"
aoqi@0: #endif
aoqi@0: #ifdef TARGET_OS_FAMILY_solaris
aoqi@0: # include "os_solaris.inline.hpp"
aoqi@0: #endif
aoqi@0: #ifdef TARGET_OS_FAMILY_windows
aoqi@0: # include "os_windows.inline.hpp"
aoqi@0: #endif
aoqi@0: #ifdef TARGET_OS_FAMILY_bsd
aoqi@0: # include "os_bsd.inline.hpp"
aoqi@0: #endif
aoqi@0: 
aoqi@0: // The direct lock/unlock calls do not force a collection if an unlock
aoqi@0: // decrements the count to zero. Avoid calling these if at all possible.
aoqi@0: 
aoqi@0: class GC_locker: public AllStatic {
aoqi@0:  private:
aoqi@0:   // The _jni_lock_count keeps track of the number of threads that are
aoqi@0:   // currently in a critical region.  It's only kept up to date when
aoqi@0:   // _needs_gc is true.  The current value is computed during
aoqi@0:   // safepointing and decremented during the slow path of GC_locker
aoqi@0:   // unlocking.
aoqi@0:   static volatile jint _jni_lock_count;  // number of jni active instances.
aoqi@0:   static volatile bool _needs_gc;        // heap is filling, we need a GC
aoqi@0:                                          // note: bool is typedef'd as jint
aoqi@0:   static volatile bool _doing_gc;        // unlock_critical() is doing a GC
aoqi@0: 
aoqi@0: #ifdef ASSERT
aoqi@0:   // This lock count is updated for all operations and is used to
aoqi@0:   // validate the jni_lock_count that is computed during safepoints.
aoqi@0:   static volatile jint _debug_jni_lock_count;
aoqi@0: #endif
aoqi@0: 
aoqi@0:   // At a safepoint, visit all threads and count the number of active
aoqi@0:   // critical sections.  This is used to ensure that all active
aoqi@0:   // critical sections are exited before a new one is started.
aoqi@0:   static void verify_critical_count() NOT_DEBUG_RETURN;
aoqi@0: 
aoqi@0:   static void jni_lock(JavaThread* thread);
aoqi@0:   static void jni_unlock(JavaThread* thread);
aoqi@0: 
aoqi@0:   static bool is_active_internal() {
aoqi@0:     verify_critical_count();
aoqi@0:     return _jni_lock_count > 0;
aoqi@0:   }
aoqi@0: 
aoqi@0:  public:
aoqi@0:   // Accessors
aoqi@0:   static bool is_active() {
aoqi@0:     assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
aoqi@0:     return is_active_internal();
aoqi@0:   }
aoqi@0:   static bool needs_gc()       { return _needs_gc;                        }
aoqi@0: 
aoqi@0:   // Shorthand
aoqi@0:   static bool is_active_and_needs_gc() {
aoqi@0:     // Use is_active_internal since _needs_gc can change from true to
aoqi@0:     // false outside of a safepoint, triggering the assert in
aoqi@0:     // is_active.
aoqi@0:     return needs_gc() && is_active_internal();
aoqi@0:   }
aoqi@0: 
aoqi@0:   // In debug mode track the locking state at all times
aoqi@0:   static void increment_debug_jni_lock_count() {
aoqi@0: #ifdef ASSERT
aoqi@0:     assert(_debug_jni_lock_count >= 0, "bad value");
aoqi@0:     Atomic::inc(&_debug_jni_lock_count);
aoqi@0: #endif
aoqi@0:   }
aoqi@0:   static void decrement_debug_jni_lock_count() {
aoqi@0: #ifdef ASSERT
aoqi@0:     assert(_debug_jni_lock_count > 0, "bad value");
aoqi@0:     Atomic::dec(&_debug_jni_lock_count);
aoqi@0: #endif
aoqi@0:   }
aoqi@0: 
aoqi@0:   // Set the current lock count
aoqi@0:   static void set_jni_lock_count(int count) {
aoqi@0:     _jni_lock_count = count;
aoqi@0:     verify_critical_count();
aoqi@0:   }
aoqi@0: 
aoqi@0:   // Sets _needs_gc if is_active() is true. Returns is_active().
aoqi@0:   static bool check_active_before_gc();
aoqi@0: 
aoqi@0:   // Stalls the caller (who should not be in a jni critical section)
aoqi@0:   // until needs_gc() clears. Note however that needs_gc() may be
aoqi@0:   // set at a subsequent safepoint and/or cleared under the
aoqi@0:   // JNICritical_lock, so the caller may not safely assert upon
aoqi@0:   // return from this method that "!needs_gc()" since that is
aoqi@0:   // not a stable predicate.
aoqi@0:   static void stall_until_clear();
aoqi@0: 
aoqi@0:   // The following two methods are used for JNI critical regions.
aoqi@0:   // If we find that we failed to perform a GC because the GC_locker
aoqi@0:   // was active, arrange for one as soon as possible by allowing
aoqi@0:   // all threads in critical regions to complete, but not allowing
aoqi@0:   // other critical regions to be entered. The reasons for that are:
aoqi@0:   // 1) a GC request won't be starved by overlapping JNI critical
aoqi@0:   //    region activities, which can cause unnecessary OutOfMemory errors.
aoqi@0:   // 2) even if allocation requests can still be satisfied before GC locker
aoqi@0:   //    becomes inactive, for example, in tenured generation possibly with
aoqi@0:   //    heap expansion, those allocations can trigger lots of safepointing
aoqi@0:   //    attempts (ineffective GC attempts) and require Heap_lock which
aoqi@0:   //    slow down allocations tremendously.
aoqi@0:   //
aoqi@0:   // Note that critical regions can be nested in a single thread, so
aoqi@0:   // we must allow threads already in critical regions to continue.
aoqi@0:   //
aoqi@0:   // JNI critical regions are the only participants in this scheme
aoqi@0:   // because they are, by spec, well bounded while in a critical region.
aoqi@0:   //
aoqi@0:   // Each of the following two method is split into a fast path and a
aoqi@0:   // slow path. JNICritical_lock is only grabbed in the slow path.
aoqi@0:   // _needs_gc is initially false and every java thread will go
aoqi@0:   // through the fast path, which simply increments or decrements the
aoqi@0:   // current thread's critical count.  When GC happens at a safepoint,
aoqi@0:   // GC_locker::is_active() is checked. Since there is no safepoint in
aoqi@0:   // the fast path of lock_critical() and unlock_critical(), there is
aoqi@0:   // no race condition between the fast path and GC. After _needs_gc
aoqi@0:   // is set at a safepoint, every thread will go through the slow path
aoqi@0:   // after the safepoint.  Since after a safepoint, each of the
aoqi@0:   // following two methods is either entered from the method entry and
aoqi@0:   // falls into the slow path, or is resumed from the safepoints in
aoqi@0:   // the method, which only exist in the slow path. So when _needs_gc
aoqi@0:   // is set, the slow path is always taken, till _needs_gc is cleared.
aoqi@0:   static void lock_critical(JavaThread* thread);
aoqi@0:   static void unlock_critical(JavaThread* thread);
aoqi@0: 
aoqi@0:   static address needs_gc_address() { return (address) &_needs_gc; }
aoqi@0: };
aoqi@0: 
aoqi@0: 
aoqi@0: // A No_GC_Verifier object can be placed in methods where one assumes that
aoqi@0: // no garbage collection will occur. The destructor will verify this property
aoqi@0: // unless the constructor is called with argument false (not verifygc).
aoqi@0: //
aoqi@0: // The check will only be done in debug mode and if verifygc true.
aoqi@0: 
aoqi@0: class No_GC_Verifier: public StackObj {
aoqi@0:  friend class Pause_No_GC_Verifier;
aoqi@0: 
aoqi@0:  protected:
aoqi@0:   bool _verifygc;
aoqi@0:   unsigned int _old_invocations;
aoqi@0: 
aoqi@0:  public:
aoqi@0: #ifdef ASSERT
aoqi@0:   No_GC_Verifier(bool verifygc = true);
aoqi@0:   ~No_GC_Verifier();
aoqi@0: #else
aoqi@0:   No_GC_Verifier(bool verifygc = true) {}
aoqi@0:   ~No_GC_Verifier() {}
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: // A Pause_No_GC_Verifier is used to temporarily pause the behavior
aoqi@0: // of a No_GC_Verifier object. If we are not in debug mode or if the
aoqi@0: // No_GC_Verifier object has a _verifygc value of false, then there
aoqi@0: // is nothing to do.
aoqi@0: 
aoqi@0: class Pause_No_GC_Verifier: public StackObj {
aoqi@0:  private:
aoqi@0:   No_GC_Verifier * _ngcv;
aoqi@0: 
aoqi@0:  public:
aoqi@0: #ifdef ASSERT
aoqi@0:   Pause_No_GC_Verifier(No_GC_Verifier * ngcv);
aoqi@0:   ~Pause_No_GC_Verifier();
aoqi@0: #else
aoqi@0:   Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {}
aoqi@0:   ~Pause_No_GC_Verifier() {}
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: 
aoqi@0: // A No_Safepoint_Verifier object will throw an assertion failure if
aoqi@0: // the current thread passes a possible safepoint while this object is
aoqi@0: // instantiated. A safepoint, will either be: an oop allocation, blocking
aoqi@0: // on a Mutex or JavaLock, or executing a VM operation.
aoqi@0: //
aoqi@0: // If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
aoqi@0: //
aoqi@0: class No_Safepoint_Verifier : public No_GC_Verifier {
aoqi@0:  friend class Pause_No_Safepoint_Verifier;
aoqi@0: 
aoqi@0:  private:
aoqi@0:   bool _activated;
aoqi@0:   Thread *_thread;
aoqi@0:  public:
aoqi@0: #ifdef ASSERT
aoqi@0:   No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) :
aoqi@0:     No_GC_Verifier(verifygc),
aoqi@0:     _activated(activated) {
aoqi@0:     _thread = Thread::current();
aoqi@0:     if (_activated) {
aoqi@0:       _thread->_allow_allocation_count++;
aoqi@0:       _thread->_allow_safepoint_count++;
aoqi@0:     }
aoqi@0:   }
aoqi@0: 
aoqi@0:   ~No_Safepoint_Verifier() {
aoqi@0:     if (_activated) {
aoqi@0:       _thread->_allow_allocation_count--;
aoqi@0:       _thread->_allow_safepoint_count--;
aoqi@0:     }
aoqi@0:   }
aoqi@0: #else
aoqi@0:   No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){}
aoqi@0:   ~No_Safepoint_Verifier() {}
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: // A Pause_No_Safepoint_Verifier is used to temporarily pause the
aoqi@0: // behavior of a No_Safepoint_Verifier object. If we are not in debug
aoqi@0: // mode then there is nothing to do. If the No_Safepoint_Verifier
aoqi@0: // object has an _activated value of false, then there is nothing to
aoqi@0: // do for safepoint and allocation checking, but there may still be
aoqi@0: // something to do for the underlying No_GC_Verifier object.
aoqi@0: 
aoqi@0: class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier {
aoqi@0:  private:
aoqi@0:   No_Safepoint_Verifier * _nsv;
aoqi@0: 
aoqi@0:  public:
aoqi@0: #ifdef ASSERT
aoqi@0:   Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
aoqi@0:     : Pause_No_GC_Verifier(nsv) {
aoqi@0: 
aoqi@0:     _nsv = nsv;
aoqi@0:     if (_nsv->_activated) {
aoqi@0:       _nsv->_thread->_allow_allocation_count--;
aoqi@0:       _nsv->_thread->_allow_safepoint_count--;
aoqi@0:     }
aoqi@0:   }
aoqi@0: 
aoqi@0:   ~Pause_No_Safepoint_Verifier() {
aoqi@0:     if (_nsv->_activated) {
aoqi@0:       _nsv->_thread->_allow_allocation_count++;
aoqi@0:       _nsv->_thread->_allow_safepoint_count++;
aoqi@0:     }
aoqi@0:   }
aoqi@0: #else
aoqi@0:   Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
aoqi@0:     : Pause_No_GC_Verifier(nsv) {}
aoqi@0:   ~Pause_No_Safepoint_Verifier() {}
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: // A SkipGCALot object is used to elide the usual effect of gc-a-lot
aoqi@0: // over a section of execution by a thread. Currently, it's used only to
aoqi@0: // prevent re-entrant calls to GC.
aoqi@0: class SkipGCALot : public StackObj {
aoqi@0:   private:
aoqi@0:    bool _saved;
aoqi@0:    Thread* _t;
aoqi@0: 
aoqi@0:   public:
aoqi@0: #ifdef ASSERT
aoqi@0:     SkipGCALot(Thread* t) : _t(t) {
aoqi@0:       _saved = _t->skip_gcalot();
aoqi@0:       _t->set_skip_gcalot(true);
aoqi@0:     }
aoqi@0: 
aoqi@0:     ~SkipGCALot() {
aoqi@0:       assert(_t->skip_gcalot(), "Save-restore protocol invariant");
aoqi@0:       _t->set_skip_gcalot(_saved);
aoqi@0:     }
aoqi@0: #else
aoqi@0:     SkipGCALot(Thread* t) { }
aoqi@0:     ~SkipGCALot() { }
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: // JRT_LEAF currently can be called from either _thread_in_Java or
aoqi@0: // _thread_in_native mode. In _thread_in_native, it is ok
aoqi@0: // for another thread to trigger GC. The rest of the JRT_LEAF
aoqi@0: // rules apply.
aoqi@0: class JRT_Leaf_Verifier : public No_Safepoint_Verifier {
aoqi@0:   static bool should_verify_GC();
aoqi@0:  public:
aoqi@0: #ifdef ASSERT
aoqi@0:   JRT_Leaf_Verifier();
aoqi@0:   ~JRT_Leaf_Verifier();
aoqi@0: #else
aoqi@0:   JRT_Leaf_Verifier() {}
aoqi@0:   ~JRT_Leaf_Verifier() {}
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: // A No_Alloc_Verifier object can be placed in methods where one assumes that
aoqi@0: // no allocation will occur. The destructor will verify this property
aoqi@0: // unless the constructor is called with argument false (not activated).
aoqi@0: //
aoqi@0: // The check will only be done in debug mode and if activated.
aoqi@0: // Note: this only makes sense at safepoints (otherwise, other threads may
aoqi@0: // allocate concurrently.)
aoqi@0: 
aoqi@0: class No_Alloc_Verifier : public StackObj {
aoqi@0:  private:
aoqi@0:   bool  _activated;
aoqi@0: 
aoqi@0:  public:
aoqi@0: #ifdef ASSERT
aoqi@0:   No_Alloc_Verifier(bool activated = true) {
aoqi@0:     _activated = activated;
aoqi@0:     if (_activated) Thread::current()->_allow_allocation_count++;
aoqi@0:   }
aoqi@0: 
aoqi@0:   ~No_Alloc_Verifier() {
aoqi@0:     if (_activated) Thread::current()->_allow_allocation_count--;
aoqi@0:   }
aoqi@0: #else
aoqi@0:   No_Alloc_Verifier(bool activated = true) {}
aoqi@0:   ~No_Alloc_Verifier() {}
aoqi@0: #endif
aoqi@0: };
aoqi@0: 
aoqi@0: #endif // SHARE_VM_MEMORY_GCLOCKER_HPP