1 /* 2 * Copyright (c) 1997, 2015, 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 "gc/shared/collectedHeap.hpp" 27 #include "gc/shared/gcLocker.inline.hpp" 28 #include "memory/resourceArea.hpp" 29 #include "logging/log.hpp" 30 #include "runtime/atomic.inline.hpp" 31 #include "runtime/thread.inline.hpp" 32 33 volatile jint GC_locker::_jni_lock_count = 0; 34 volatile bool GC_locker::_needs_gc = false; 35 volatile bool GC_locker::_doing_gc = false; 36 37 #ifdef ASSERT 38 volatile jint GC_locker::_debug_jni_lock_count = 0; 39 #endif 40 41 42 #ifdef ASSERT 43 void GC_locker::verify_critical_count() { 44 if (SafepointSynchronize::is_at_safepoint()) { 45 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree"); 46 int count = 0; 47 // Count the number of threads with critical operations in progress 48 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) { 49 if (thr->in_critical()) { 50 count++; 51 } 52 } 53 if (_jni_lock_count != count) { 54 tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count); 55 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) { 56 if (thr->in_critical()) { 57 tty->print_cr(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical()); 58 } 59 } 60 } 61 assert(_jni_lock_count == count, "must be equal"); 62 } 63 } 64 65 // In debug mode track the locking state at all times 66 void GC_locker::increment_debug_jni_lock_count() { 67 assert(_debug_jni_lock_count >= 0, "bad value"); 68 Atomic::inc(&_debug_jni_lock_count); 69 } 70 71 void GC_locker::decrement_debug_jni_lock_count() { 72 assert(_debug_jni_lock_count > 0, "bad value"); 73 Atomic::dec(&_debug_jni_lock_count); 74 } 75 #endif 76 77 void GC_locker::log_debug_jni(const char* msg) { 78 LogHandle(gc, jni) log; 79 if (log.is_debug()) { 80 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8 81 log.debug("%s Thread \"%s\" %d locked.", msg, Thread::current()->name(), _jni_lock_count); 82 } 83 } 84 85 bool GC_locker::check_active_before_gc() { 86 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint"); 87 if (is_active() && !_needs_gc) { 88 verify_critical_count(); 89 _needs_gc = true; 90 log_debug_jni("Setting _needs_gc."); 91 } 92 return is_active(); 93 } 94 95 void GC_locker::stall_until_clear() { 96 assert(!JavaThread::current()->in_critical(), "Would deadlock"); 97 MutexLocker ml(JNICritical_lock); 98 99 if (needs_gc()) { 100 log_debug_jni("Allocation failed. Thread stalled by JNI critical section."); 101 } 102 103 // Wait for _needs_gc to be cleared 104 while (needs_gc()) { 105 JNICritical_lock->wait(); 106 } 107 } 108 109 void GC_locker::jni_lock(JavaThread* thread) { 110 assert(!thread->in_critical(), "shouldn't currently be in a critical region"); 111 MutexLocker mu(JNICritical_lock); 112 // Block entering threads if we know at least one thread is in a 113 // JNI critical region and we need a GC. 114 // We check that at least one thread is in a critical region before 115 // blocking because blocked threads are woken up by a thread exiting 116 // a JNI critical region. 117 while (is_active_and_needs_gc() || _doing_gc) { 118 JNICritical_lock->wait(); 119 } 120 thread->enter_critical(); 121 _jni_lock_count++; 122 increment_debug_jni_lock_count(); 123 } 124 125 void GC_locker::jni_unlock(JavaThread* thread) { 126 assert(thread->in_last_critical(), "should be exiting critical region"); 127 MutexLocker mu(JNICritical_lock); 128 _jni_lock_count--; 129 decrement_debug_jni_lock_count(); 130 thread->exit_critical(); 131 if (needs_gc() && !is_active_internal()) { 132 // We're the last thread out. Cause a GC to occur. 133 _doing_gc = true; 134 { 135 // Must give up the lock while at a safepoint 136 MutexUnlocker munlock(JNICritical_lock); 137 log_debug_jni("Performing GC after exiting critical section."); 138 Universe::heap()->collect(GCCause::_gc_locker); 139 } 140 _doing_gc = false; 141 _needs_gc = false; 142 JNICritical_lock->notify_all(); 143 } 144 } 145 146 // Implementation of No_GC_Verifier 147 148 #ifdef ASSERT 149 150 No_GC_Verifier::No_GC_Verifier(bool verifygc) { 151 _verifygc = verifygc; 152 if (_verifygc) { 153 CollectedHeap* h = Universe::heap(); 154 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 155 _old_invocations = h->total_collections(); 156 } 157 } 158 159 160 No_GC_Verifier::~No_GC_Verifier() { 161 if (_verifygc) { 162 CollectedHeap* h = Universe::heap(); 163 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 164 if (_old_invocations != h->total_collections()) { 165 fatal("collection in a No_GC_Verifier secured function"); 166 } 167 } 168 } 169 170 Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) { 171 _ngcv = ngcv; 172 if (_ngcv->_verifygc) { 173 // if we were verifying, then make sure that nothing is 174 // wrong before we "pause" verification 175 CollectedHeap* h = Universe::heap(); 176 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 177 if (_ngcv->_old_invocations != h->total_collections()) { 178 fatal("collection in a No_GC_Verifier secured function"); 179 } 180 } 181 } 182 183 184 Pause_No_GC_Verifier::~Pause_No_GC_Verifier() { 185 if (_ngcv->_verifygc) { 186 // if we were verifying before, then reenable verification 187 CollectedHeap* h = Universe::heap(); 188 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 189 _ngcv->_old_invocations = h->total_collections(); 190 } 191 } 192 193 194 // JRT_LEAF rules: 195 // A JRT_LEAF method may not interfere with safepointing by 196 // 1) acquiring or blocking on a Mutex or JavaLock - checked 197 // 2) allocating heap memory - checked 198 // 3) executing a VM operation - checked 199 // 4) executing a system call (including malloc) that could block or grab a lock 200 // 5) invoking GC 201 // 6) reaching a safepoint 202 // 7) running too long 203 // Nor may any method it calls. 204 JRT_Leaf_Verifier::JRT_Leaf_Verifier() 205 : No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC()) 206 { 207 } 208 209 JRT_Leaf_Verifier::~JRT_Leaf_Verifier() 210 { 211 } 212 213 bool JRT_Leaf_Verifier::should_verify_GC() { 214 switch (JavaThread::current()->thread_state()) { 215 case _thread_in_Java: 216 // is in a leaf routine, there must be no safepoint. 217 return true; 218 case _thread_in_native: 219 // A native thread is not subject to safepoints. 220 // Even while it is in a leaf routine, GC is ok 221 return false; 222 default: 223 // Leaf routines cannot be called from other contexts. 224 ShouldNotReachHere(); 225 return false; 226 } 227 } 228 #endif