1 /* 2 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 24 25 #include "precompiled.hpp" 26 #include "memory/gcLocker.inline.hpp" 27 #include "memory/resourceArea.hpp" 28 #include "memory/sharedHeap.hpp" 29 30 volatile jint GC_locker::_jni_lock_count = 0; 31 volatile jint GC_locker::_lock_count = 0; 32 volatile bool GC_locker::_needs_gc = false; 33 volatile bool GC_locker::_doing_gc = false; 34 35 #ifdef ASSERT 36 volatile jint GC_locker::_debug_jni_lock_count = 0; 37 #endif 38 39 40 #ifdef ASSERT 41 void GC_locker::verify_critical_count() { 42 if (SafepointSynchronize::is_at_safepoint()) { 43 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree"); 44 int count = 0; 45 // Count the number of threads with critical operations in progress 46 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) { 47 if (thr->in_critical()) { 48 count++; 49 } 50 } 51 if (_jni_lock_count != count) { 52 tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count); 53 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) { 54 if (thr->in_critical()) { 55 tty->print_cr(INTPTR_FORMAT " in_critical %d", thr, thr->in_critical()); 56 } 57 } 58 } 59 assert(_jni_lock_count == count, "must be equal"); 60 } 61 } 62 #endif 63 64 bool GC_locker::check_active_before_gc() { 65 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint"); 66 if (is_active() && !_needs_gc) { 67 verify_critical_count(); 68 _needs_gc = true; 69 if (PrintJNIGCStalls && PrintGCDetails) { 70 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8 71 gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.", 72 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count); 73 } 74 75 } 76 return is_active(); 77 } 78 79 void GC_locker::stall_until_clear() { 80 assert(!JavaThread::current()->in_critical(), "Would deadlock"); 81 MutexLocker ml(JNICritical_lock); 82 83 if (needs_gc()) { 84 if (PrintJNIGCStalls && PrintGCDetails) { 85 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8 86 gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.", 87 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count); 88 } 89 } 90 91 // Wait for _needs_gc to be cleared 92 while (needs_gc()) { 93 JNICritical_lock->wait(); 94 } 95 } 96 97 void GC_locker::jni_lock(JavaThread* thread) { 98 assert(!thread->in_critical(), "shouldn't currently be in a critical region"); 99 MutexLocker mu(JNICritical_lock); 100 // Block entering threads if we know at least one thread is in a 101 // JNI critical region and we need a GC. 102 // We check that at least one thread is in a critical region before 103 // blocking because blocked threads are woken up by a thread exiting 104 // a JNI critical region. 105 while ((needs_gc() && is_jni_active()) || _doing_gc) { 106 JNICritical_lock->wait(); 107 } 108 thread->enter_critical(); 109 _jni_lock_count++; 110 increment_debug_jni_lock_count(); 111 } 112 113 void GC_locker::jni_unlock(JavaThread* thread) { 114 assert(thread->in_last_critical(), "should be exiting critical region"); 115 MutexLocker mu(JNICritical_lock); 116 _jni_lock_count--; 117 decrement_debug_jni_lock_count(); 118 thread->exit_critical(); 119 if (needs_gc() && !is_jni_active()) { 120 // We're the last thread out. Cause a GC to occur. 121 // GC will also check is_active, so this check is not 122 // strictly needed. It's added here to make it clear that 123 // the GC will NOT be performed if any other caller 124 // of GC_locker::lock() still needs GC locked. 125 if (!is_active_internal()) { 126 _doing_gc = true; 127 { 128 // Must give up the lock while at a safepoint 129 MutexUnlocker munlock(JNICritical_lock); 130 if (PrintJNIGCStalls && PrintGCDetails) { 131 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8 132 gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked", 133 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count); 134 } 135 Universe::heap()->collect(GCCause::_gc_locker); 136 } 137 _doing_gc = false; 138 } 139 140 _needs_gc = false; 141 JNICritical_lock->notify_all(); 142 } 143 } 144 145 // Implementation of No_GC_Verifier 146 147 #ifdef ASSERT 148 149 No_GC_Verifier::No_GC_Verifier(bool verifygc) { 150 _verifygc = verifygc; 151 if (_verifygc) { 152 CollectedHeap* h = Universe::heap(); 153 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 154 _old_invocations = h->total_collections(); 155 } 156 } 157 158 159 No_GC_Verifier::~No_GC_Verifier() { 160 if (_verifygc) { 161 CollectedHeap* h = Universe::heap(); 162 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 163 if (_old_invocations != h->total_collections()) { 164 fatal("collection in a No_GC_Verifier secured function"); 165 } 166 } 167 } 168 169 Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) { 170 _ngcv = ngcv; 171 if (_ngcv->_verifygc) { 172 // if we were verifying, then make sure that nothing is 173 // wrong before we "pause" verification 174 CollectedHeap* h = Universe::heap(); 175 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 176 if (_ngcv->_old_invocations != h->total_collections()) { 177 fatal("collection in a No_GC_Verifier secured function"); 178 } 179 } 180 } 181 182 183 Pause_No_GC_Verifier::~Pause_No_GC_Verifier() { 184 if (_ngcv->_verifygc) { 185 // if we were verifying before, then reenable verification 186 CollectedHeap* h = Universe::heap(); 187 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 188 _ngcv->_old_invocations = h->total_collections(); 189 } 190 } 191 192 193 // JRT_LEAF rules: 194 // A JRT_LEAF method may not interfere with safepointing by 195 // 1) acquiring or blocking on a Mutex or JavaLock - checked 196 // 2) allocating heap memory - checked 197 // 3) executing a VM operation - checked 198 // 4) executing a system call (including malloc) that could block or grab a lock 199 // 5) invoking GC 200 // 6) reaching a safepoint 201 // 7) running too long 202 // Nor may any method it calls. 203 JRT_Leaf_Verifier::JRT_Leaf_Verifier() 204 : No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC()) 205 { 206 } 207 208 JRT_Leaf_Verifier::~JRT_Leaf_Verifier() 209 { 210 } 211 212 bool JRT_Leaf_Verifier::should_verify_GC() { 213 switch (JavaThread::current()->thread_state()) { 214 case _thread_in_Java: 215 // is in a leaf routine, there must be no safepoint. 216 return true; 217 case _thread_in_native: 218 // A native thread is not subject to safepoints. 219 // Even while it is in a leaf routine, GC is ok 220 return false; 221 default: 222 // Leaf routines cannot be called from other contexts. 223 ShouldNotReachHere(); 224 return false; 225 } 226 } 227 #endif