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 "runtime/atomic.inline.hpp" 30 #include "runtime/thread.inline.hpp" 31 32 volatile jint GC_locker::_jni_lock_count = 0; 33 volatile bool GC_locker::_needs_gc = false; 34 volatile bool GC_locker::_doing_gc = false; 35 36 #ifdef ASSERT 37 volatile jint GC_locker::_debug_jni_lock_count = 0; 38 #endif 39 40 41 #ifdef ASSERT 42 void GC_locker::verify_critical_count() { 43 if (SafepointSynchronize::is_at_safepoint()) { 44 assert(!needs_gc() || _debug_jni_lock_count == _jni_lock_count, "must agree"); 45 int count = 0; 46 // Count the number of threads with critical operations in progress 47 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) { 48 if (thr->in_critical()) { 49 count++; 50 } 51 } 52 if (_jni_lock_count != count) { 53 tty->print_cr("critical counts don't match: %d != %d", _jni_lock_count, count); 54 for (JavaThread* thr = Threads::first(); thr; thr = thr->next()) { 55 if (thr->in_critical()) { 56 tty->print_cr(INTPTR_FORMAT " in_critical %d", p2i(thr), thr->in_critical()); 57 } 58 } 59 } 60 assert(_jni_lock_count == count, "must be equal"); 61 } 62 } 63 64 // In debug mode track the locking state at all times 65 void GC_locker::increment_debug_jni_lock_count() { 66 assert(_debug_jni_lock_count >= 0, "bad value"); 67 Atomic::inc(&_debug_jni_lock_count); 68 } 69 70 void GC_locker::decrement_debug_jni_lock_count() { 71 assert(_debug_jni_lock_count > 0, "bad value"); 72 Atomic::dec(&_debug_jni_lock_count); 73 } 74 #endif 75 76 bool GC_locker::check_active_before_gc() { 77 assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint"); 78 if (is_active() && !_needs_gc) { 79 verify_critical_count(); 80 _needs_gc = true; 81 if (PrintJNIGCStalls && PrintGCDetails) { 82 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8 83 gclog_or_tty->print_cr("%.3f: Setting _needs_gc. Thread \"%s\" %d locked.", 84 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count); 85 } 86 87 } 88 return is_active(); 89 } 90 91 void GC_locker::stall_until_clear() { 92 assert(!JavaThread::current()->in_critical(), "Would deadlock"); 93 MutexLocker ml(JNICritical_lock); 94 95 if (needs_gc()) { 96 if (PrintJNIGCStalls && PrintGCDetails) { 97 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8 98 gclog_or_tty->print_cr("%.3f: Allocation failed. Thread \"%s\" is stalled by JNI critical section, %d locked.", 99 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count); 100 } 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 if (PrintJNIGCStalls && PrintGCDetails) { 138 ResourceMark rm; // JavaThread::name() allocates to convert to UTF8 139 gclog_or_tty->print_cr("%.3f: Thread \"%s\" is performing GC after exiting critical section, %d locked", 140 gclog_or_tty->time_stamp().seconds(), Thread::current()->name(), _jni_lock_count); 141 } 142 Universe::heap()->collect(GCCause::_gc_locker); 143 } 144 _doing_gc = false; 145 _needs_gc = false; 146 JNICritical_lock->notify_all(); 147 } 148 } 149 150 // Implementation of No_GC_Verifier 151 152 #ifdef ASSERT 153 154 No_GC_Verifier::No_GC_Verifier(bool verifygc) { 155 _verifygc = verifygc; 156 if (_verifygc) { 157 CollectedHeap* h = Universe::heap(); 158 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 159 _old_invocations = h->total_collections(); 160 } 161 } 162 163 164 No_GC_Verifier::~No_GC_Verifier() { 165 if (_verifygc) { 166 CollectedHeap* h = Universe::heap(); 167 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 168 if (_old_invocations != h->total_collections()) { 169 fatal("collection in a No_GC_Verifier secured function"); 170 } 171 } 172 } 173 174 Pause_No_GC_Verifier::Pause_No_GC_Verifier(No_GC_Verifier * ngcv) { 175 _ngcv = ngcv; 176 if (_ngcv->_verifygc) { 177 // if we were verifying, then make sure that nothing is 178 // wrong before we "pause" verification 179 CollectedHeap* h = Universe::heap(); 180 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 181 if (_ngcv->_old_invocations != h->total_collections()) { 182 fatal("collection in a No_GC_Verifier secured function"); 183 } 184 } 185 } 186 187 188 Pause_No_GC_Verifier::~Pause_No_GC_Verifier() { 189 if (_ngcv->_verifygc) { 190 // if we were verifying before, then reenable verification 191 CollectedHeap* h = Universe::heap(); 192 assert(!h->is_gc_active(), "GC active during No_GC_Verifier"); 193 _ngcv->_old_invocations = h->total_collections(); 194 } 195 } 196 197 198 // JRT_LEAF rules: 199 // A JRT_LEAF method may not interfere with safepointing by 200 // 1) acquiring or blocking on a Mutex or JavaLock - checked 201 // 2) allocating heap memory - checked 202 // 3) executing a VM operation - checked 203 // 4) executing a system call (including malloc) that could block or grab a lock 204 // 5) invoking GC 205 // 6) reaching a safepoint 206 // 7) running too long 207 // Nor may any method it calls. 208 JRT_Leaf_Verifier::JRT_Leaf_Verifier() 209 : No_Safepoint_Verifier(true, JRT_Leaf_Verifier::should_verify_GC()) 210 { 211 } 212 213 JRT_Leaf_Verifier::~JRT_Leaf_Verifier() 214 { 215 } 216 217 bool JRT_Leaf_Verifier::should_verify_GC() { 218 switch (JavaThread::current()->thread_state()) { 219 case _thread_in_Java: 220 // is in a leaf routine, there must be no safepoint. 221 return true; 222 case _thread_in_native: 223 // A native thread is not subject to safepoints. 224 // Even while it is in a leaf routine, GC is ok 225 return false; 226 default: 227 // Leaf routines cannot be called from other contexts. 228 ShouldNotReachHere(); 229 return false; 230 } 231 } 232 #endif