jdk8-mips64-public/hotspot: src/share/vm/memory/gcLocker.hpp@2c022e432e10 (annotated)

src/share/vm/memory/gcLocker.hpp@2c022e432e10 (annotated)

src/share/vm/memory/gcLocker.hpp

Fri, 20 Sep 2013 10:53:28 +0200

author: stefank
date: Fri, 20 Sep 2013 10:53:28 +0200
changeset 5769: 2c022e432e10
parent 4299: f34d701e952e
child 6198: 55fb97c4c58d
permissions: -rw-r--r--

8024974: Incorrect use of GC_locker::is_active()
Summary: SymbolTable and StringTable can make calls to GC_locker::is_active() outside a safepoint. This isn't safe because the GC_locker active state (lock count) is only updated at a safepoint and only remains valid as long as _needs_gc is true. However, outside a safepoint_needs_gc can change to false at any time, which makes it impossible to do a correct call to is_active() in that context. In this case these calls can just be removed since the input argument to basic_add() should never be on the heap and so there's no need to check the GC_locker state. This change also adjusts the assert() in is_active() to makes sure all calls to this function are always done under a safepoint.
Reviewed-by: brutisso, dcubed
Contributed-by: per.liden@oracle.com

 /*
  * Copyright (c) 1997, 2012, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */
 #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

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/memory/gcLocker.hpp@2c022e432e10 (annotated)

src/share/vm/memory/gcLocker.hpp