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 /*

  * Copyright (c) 1997, 2014, 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.

  *

  */

 #include "precompiled.hpp"

 #include "memory/gcLocker.inline.hpp"

 #include "memory/resourceArea.hpp"

 #include "memory/sharedHeap.hpp"

 #include "runtime/thread.inline.hpp"

 volatile jint GC_locker::_jni_lock_count = 0;

 volatile bool GC_locker::_needs_gc       = false;

 volatile bool GC_locker::_doing_gc       = false;

 unsigned int  GC_locker::_total_collections = 0;

 #ifdef ASSERT

 volatile jint GC_locker::_debug_jni_lock_count = 0;

 #endif

 #ifdef ASSERT

 void GC_locker::verify_critical_count() {

   if (SafepointSynchronize::is_at_safepoint()) {

     assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree");

     int count = 0;

     // Count the number of threads with critical operations in progress

     for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {

       if (thr->in_critical()) {

         count++;

       }

     }

     if (_jni_lock_count != count) {

       tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count);

       for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) {

         if (thr->in_critical()) {

           tty->print_cr(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical());

         }

       }

     }

     assert(_jni_lock_count == count, "must be equal");

   }

 }

 #endif

 bool GC_locker::check_active_before_gc() {

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

   if (is_active() && !_needs_gc) {

     verify_critical_count();

     _needs_gc = true;

     if (PrintJNIGCStalls && PrintGCDetails) {

       ResourceMark rm; // JavaThread::name() allocates to convert to UTF8

       gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.",

                              gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);

     }

   }

   return is_active();

 }

 void GC_locker::stall_until_clear() {

   assert(!JavaThread::current()->in_critical(), "Would deadlock");

   MutexLocker   ml(JNICritical_lock);

   if (needs_gc()) {

     if (PrintJNIGCStalls && PrintGCDetails) {

       ResourceMark rm; // JavaThread::name() allocates to convert to UTF8

       gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.",

                              gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);

     }

   }

   // Wait for _needs_gc  to be cleared

   while (needs_gc()) {

     JNICritical_lock->wait();

   }

 }

 bool GC_locker::should_discard(GCCause::Cause cause, uint total_collections) {

   return (cause == GCCause::_gc_locker) &&

          (_total_collections != total_collections);

 }

 void GC_locker::jni_lock(JavaThread* thread) {

   assert(!thread->in_critical(), "shouldn't currently be in a critical region");

   MutexLocker mu(JNICritical_lock);

   // Block entering threads if we know at least one thread is in a

   // JNI critical region and we need a GC.

   // We check that at least one thread is in a critical region before

   // blocking because blocked threads are woken up by a thread exiting

   // a JNI critical region.

   while (is_active_and_needs_gc() || _doing_gc) {

     JNICritical_lock->wait();

   }

   thread->enter_critical();

   _jni_lock_count++;

   increment_debug_jni_lock_count();

 }

 void GC_locker::jni_unlock(JavaThread* thread) {

   assert(thread->in_last_critical(), "should be exiting critical region");

   MutexLocker mu(JNICritical_lock);

   _jni_lock_count--;

   decrement_debug_jni_lock_count();

   thread->exit_critical();

   if (needs_gc() && !is_active_internal()) {

     // We're the last thread out. Request a GC.

     // Capture the current total collections, to allow detection of

     // other collections that make this one unnecessary.  The value of

     // total_collections() is only changed at a safepoint, so there

     // must not be a safepoint between the lock becoming inactive and

     // getting the count, else there may be unnecessary GCLocker GCs.

     _total_collections = Universe::heap()->total_collections();

     _doing_gc = true;

     {

       // Must give up the lock while at a safepoint

       MutexUnlocker munlock(JNICritical_lock);

       if (PrintJNIGCStalls && PrintGCDetails) {

         ResourceMark rm; // JavaThread::name() allocates to convert to UTF8

         gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked",

             gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count);

       }

       Universe::heap()->collect(GCCause::_gc_locker);

     }

     _doing_gc = false;

     _needs_gc = false;

     JNICritical_lock->notify_all();

   }

 }

 // Implementation of No_GC_Verifier

 #ifdef ASSERT

 No_GC_Verifier::No_GC_Verifier(bool verifygc) {

   _verifygc = verifygc;

   if (_verifygc) {

     CollectedHeap* h = Universe::heap();

     assert(!h->is_gc_active(), "GC active during No_GC_Verifier");

     _old_invocations = h->total_collections();

   }

 }

 No_GC_Verifier::~No_GC_Verifier() {

   if (_verifygc) {

     CollectedHeap* h = Universe::heap();

     assert(!h->is_gc_active(), "GC active during No_GC_Verifier");

     if (_old_invocations != h->total_collections()) {

       fatal("collection in a No_GC_Verifier secured function");

     }

   }

 }

 Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {

   _ngcv = ngcv;

   if (_ngcv->_verifygc) {

     // if we were verifying, then make sure that nothing is

     // wrong before we "pause" verification

     CollectedHeap* h = Universe::heap();

     assert(!h->is_gc_active(), "GC active during No_GC_Verifier");

     if (_ngcv->_old_invocations != h->total_collections()) {

       fatal("collection in a No_GC_Verifier secured function");

     }

   }

 }

 Pause_No_GC_Verifier::~Pause_No_GC_Verifier() {

   if (_ngcv->_verifygc) {

     // if we were verifying before, then reenable verification

     CollectedHeap* h = Universe::heap();

     assert(!h->is_gc_active(), "GC active during No_GC_Verifier");

     _ngcv->_old_invocations = h->total_collections();

   }

 }

 // JRT_LEAF rules:

 // A JRT_LEAF method may not interfere with safepointing by

 //   1) acquiring or blocking on a Mutex or JavaLock - checked

 //   2) allocating heap memory - checked

 //   3) executing a VM operation - checked

 //   4) executing a system call (including malloc) that could block or grab a lock

 //   5) invoking GC

 //   6) reaching a safepoint

 //   7) running too long

 // Nor may any method it calls.

 JRT_Leaf_Verifier::JRT_Leaf_Verifier()

   : No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC())

 {

 }

 JRT_Leaf_Verifier::~JRT_Leaf_Verifier()

 {

 }

 bool JRT_Leaf_Verifier::should_verify_GC() {

   switch (JavaThread::current()->thread_state()) {

   case _thread_in_Java:

     // is in a leaf routine, there must be no safepoint.

     return true;

   case _thread_in_native:

     // A native thread is not subject to safepoints.

     // Even while it is in a leaf routine, GC is ok

     return false;

   default:

     // Leaf routines cannot be called from other contexts.

     ShouldNotReachHere();

     return false;

   }

 }

 #endif