1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/memory/gcLocker.hpp Wed Apr 27 01:25:04 2016 +0800
1.3 @@ -0,0 +1,352 @@
1.4 +/*
1.5 + * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
1.6 + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
1.7 + *
1.8 + * This code is free software; you can redistribute it and/or modify it
1.9 + * under the terms of the GNU General Public License version 2 only, as
1.10 + * published by the Free Software Foundation.
1.11 + *
1.12 + * This code is distributed in the hope that it will be useful, but WITHOUT
1.13 + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
1.14 + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
1.15 + * version 2 for more details (a copy is included in the LICENSE file that
1.16 + * accompanied this code).
1.17 + *
1.18 + * You should have received a copy of the GNU General Public License version
1.19 + * 2 along with this work; if not, write to the Free Software Foundation,
1.20 + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
1.21 + *
1.22 + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
1.23 + * or visit www.oracle.com if you need additional information or have any
1.24 + * questions.
1.25 + *
1.26 + */
1.27 +
1.28 +#ifndef SHARE_VM_MEMORY_GCLOCKER_HPP
1.29 +#define SHARE_VM_MEMORY_GCLOCKER_HPP
1.30 +
1.31 +#include "gc_interface/collectedHeap.hpp"
1.32 +#include "memory/genCollectedHeap.hpp"
1.33 +#include "memory/universe.hpp"
1.34 +#include "oops/oop.hpp"
1.35 +#include "runtime/thread.inline.hpp"
1.36 +#ifdef TARGET_OS_FAMILY_linux
1.37 +# include "os_linux.inline.hpp"
1.38 +#endif
1.39 +#ifdef TARGET_OS_FAMILY_solaris
1.40 +# include "os_solaris.inline.hpp"
1.41 +#endif
1.42 +#ifdef TARGET_OS_FAMILY_windows
1.43 +# include "os_windows.inline.hpp"
1.44 +#endif
1.45 +#ifdef TARGET_OS_FAMILY_bsd
1.46 +# include "os_bsd.inline.hpp"
1.47 +#endif
1.48 +
1.49 +// The direct lock/unlock calls do not force a collection if an unlock
1.50 +// decrements the count to zero. Avoid calling these if at all possible.
1.51 +
1.52 +class GC_locker: public AllStatic {
1.53 + private:
1.54 + // The _jni_lock_count keeps track of the number of threads that are
1.55 + // currently in a critical region. It's only kept up to date when
1.56 + // _needs_gc is true. The current value is computed during
1.57 + // safepointing and decremented during the slow path of GC_locker
1.58 + // unlocking.
1.59 + static volatile jint _jni_lock_count; // number of jni active instances.
1.60 + static volatile bool _needs_gc; // heap is filling, we need a GC
1.61 + // note: bool is typedef'd as jint
1.62 + static volatile bool _doing_gc; // unlock_critical() is doing a GC
1.63 +
1.64 +#ifdef ASSERT
1.65 + // This lock count is updated for all operations and is used to
1.66 + // validate the jni_lock_count that is computed during safepoints.
1.67 + static volatile jint _debug_jni_lock_count;
1.68 +#endif
1.69 +
1.70 + // At a safepoint, visit all threads and count the number of active
1.71 + // critical sections. This is used to ensure that all active
1.72 + // critical sections are exited before a new one is started.
1.73 + static void verify_critical_count() NOT_DEBUG_RETURN;
1.74 +
1.75 + static void jni_lock(JavaThread* thread);
1.76 + static void jni_unlock(JavaThread* thread);
1.77 +
1.78 + static bool is_active_internal() {
1.79 + verify_critical_count();
1.80 + return _jni_lock_count > 0;
1.81 + }
1.82 +
1.83 + public:
1.84 + // Accessors
1.85 + static bool is_active() {
1.86 + assert(SafepointSynchronize::is_at_safepoint(), "only read at safepoint");
1.87 + return is_active_internal();
1.88 + }
1.89 + static bool needs_gc() { return _needs_gc; }
1.90 +
1.91 + // Shorthand
1.92 + static bool is_active_and_needs_gc() {
1.93 + // Use is_active_internal since _needs_gc can change from true to
1.94 + // false outside of a safepoint, triggering the assert in
1.95 + // is_active.
1.96 + return needs_gc() && is_active_internal();
1.97 + }
1.98 +
1.99 + // In debug mode track the locking state at all times
1.100 + static void increment_debug_jni_lock_count() {
1.101 +#ifdef ASSERT
1.102 + assert(_debug_jni_lock_count >= 0, "bad value");
1.103 + Atomic::inc(&_debug_jni_lock_count);
1.104 +#endif
1.105 + }
1.106 + static void decrement_debug_jni_lock_count() {
1.107 +#ifdef ASSERT
1.108 + assert(_debug_jni_lock_count > 0, "bad value");
1.109 + Atomic::dec(&_debug_jni_lock_count);
1.110 +#endif
1.111 + }
1.112 +
1.113 + // Set the current lock count
1.114 + static void set_jni_lock_count(int count) {
1.115 + _jni_lock_count = count;
1.116 + verify_critical_count();
1.117 + }
1.118 +
1.119 + // Sets _needs_gc if is_active() is true. Returns is_active().
1.120 + static bool check_active_before_gc();
1.121 +
1.122 + // Stalls the caller (who should not be in a jni critical section)
1.123 + // until needs_gc() clears. Note however that needs_gc() may be
1.124 + // set at a subsequent safepoint and/or cleared under the
1.125 + // JNICritical_lock, so the caller may not safely assert upon
1.126 + // return from this method that "!needs_gc()" since that is
1.127 + // not a stable predicate.
1.128 + static void stall_until_clear();
1.129 +
1.130 + // The following two methods are used for JNI critical regions.
1.131 + // If we find that we failed to perform a GC because the GC_locker
1.132 + // was active, arrange for one as soon as possible by allowing
1.133 + // all threads in critical regions to complete, but not allowing
1.134 + // other critical regions to be entered. The reasons for that are:
1.135 + // 1) a GC request won't be starved by overlapping JNI critical
1.136 + // region activities, which can cause unnecessary OutOfMemory errors.
1.137 + // 2) even if allocation requests can still be satisfied before GC locker
1.138 + // becomes inactive, for example, in tenured generation possibly with
1.139 + // heap expansion, those allocations can trigger lots of safepointing
1.140 + // attempts (ineffective GC attempts) and require Heap_lock which
1.141 + // slow down allocations tremendously.
1.142 + //
1.143 + // Note that critical regions can be nested in a single thread, so
1.144 + // we must allow threads already in critical regions to continue.
1.145 + //
1.146 + // JNI critical regions are the only participants in this scheme
1.147 + // because they are, by spec, well bounded while in a critical region.
1.148 + //
1.149 + // Each of the following two method is split into a fast path and a
1.150 + // slow path. JNICritical_lock is only grabbed in the slow path.
1.151 + // _needs_gc is initially false and every java thread will go
1.152 + // through the fast path, which simply increments or decrements the
1.153 + // current thread's critical count. When GC happens at a safepoint,
1.154 + // GC_locker::is_active() is checked. Since there is no safepoint in
1.155 + // the fast path of lock_critical() and unlock_critical(), there is
1.156 + // no race condition between the fast path and GC. After _needs_gc
1.157 + // is set at a safepoint, every thread will go through the slow path
1.158 + // after the safepoint. Since after a safepoint, each of the
1.159 + // following two methods is either entered from the method entry and
1.160 + // falls into the slow path, or is resumed from the safepoints in
1.161 + // the method, which only exist in the slow path. So when _needs_gc
1.162 + // is set, the slow path is always taken, till _needs_gc is cleared.
1.163 + static void lock_critical(JavaThread* thread);
1.164 + static void unlock_critical(JavaThread* thread);
1.165 +
1.166 + static address needs_gc_address() { return (address) &_needs_gc; }
1.167 +};
1.168 +
1.169 +
1.170 +// A No_GC_Verifier object can be placed in methods where one assumes that
1.171 +// no garbage collection will occur. The destructor will verify this property
1.172 +// unless the constructor is called with argument false (not verifygc).
1.173 +//
1.174 +// The check will only be done in debug mode and if verifygc true.
1.175 +
1.176 +class No_GC_Verifier: public StackObj {
1.177 + friend class Pause_No_GC_Verifier;
1.178 +
1.179 + protected:
1.180 + bool _verifygc;
1.181 + unsigned int _old_invocations;
1.182 +
1.183 + public:
1.184 +#ifdef ASSERT
1.185 + No_GC_Verifier(bool verifygc = true);
1.186 + ~No_GC_Verifier();
1.187 +#else
1.188 + No_GC_Verifier(bool verifygc = true) {}
1.189 + ~No_GC_Verifier() {}
1.190 +#endif
1.191 +};
1.192 +
1.193 +// A Pause_No_GC_Verifier is used to temporarily pause the behavior
1.194 +// of a No_GC_Verifier object. If we are not in debug mode or if the
1.195 +// No_GC_Verifier object has a _verifygc value of false, then there
1.196 +// is nothing to do.
1.197 +
1.198 +class Pause_No_GC_Verifier: public StackObj {
1.199 + private:
1.200 + No_GC_Verifier * _ngcv;
1.201 +
1.202 + public:
1.203 +#ifdef ASSERT
1.204 + Pause_No_GC_Verifier(No_GC_Verifier * ngcv);
1.205 + ~Pause_No_GC_Verifier();
1.206 +#else
1.207 + Pause_No_GC_Verifier(No_GC_Verifier * ngcv) {}
1.208 + ~Pause_No_GC_Verifier() {}
1.209 +#endif
1.210 +};
1.211 +
1.212 +
1.213 +// A No_Safepoint_Verifier object will throw an assertion failure if
1.214 +// the current thread passes a possible safepoint while this object is
1.215 +// instantiated. A safepoint, will either be: an oop allocation, blocking
1.216 +// on a Mutex or JavaLock, or executing a VM operation.
1.217 +//
1.218 +// If StrictSafepointChecks is turned off, it degrades into a No_GC_Verifier
1.219 +//
1.220 +class No_Safepoint_Verifier : public No_GC_Verifier {
1.221 + friend class Pause_No_Safepoint_Verifier;
1.222 +
1.223 + private:
1.224 + bool _activated;
1.225 + Thread *_thread;
1.226 + public:
1.227 +#ifdef ASSERT
1.228 + No_Safepoint_Verifier(bool activated = true, bool verifygc = true ) :
1.229 + No_GC_Verifier(verifygc),
1.230 + _activated(activated) {
1.231 + _thread = Thread::current();
1.232 + if (_activated) {
1.233 + _thread->_allow_allocation_count++;
1.234 + _thread->_allow_safepoint_count++;
1.235 + }
1.236 + }
1.237 +
1.238 + ~No_Safepoint_Verifier() {
1.239 + if (_activated) {
1.240 + _thread->_allow_allocation_count--;
1.241 + _thread->_allow_safepoint_count--;
1.242 + }
1.243 + }
1.244 +#else
1.245 + No_Safepoint_Verifier(bool activated = true, bool verifygc = true) : No_GC_Verifier(verifygc){}
1.246 + ~No_Safepoint_Verifier() {}
1.247 +#endif
1.248 +};
1.249 +
1.250 +// A Pause_No_Safepoint_Verifier is used to temporarily pause the
1.251 +// behavior of a No_Safepoint_Verifier object. If we are not in debug
1.252 +// mode then there is nothing to do. If the No_Safepoint_Verifier
1.253 +// object has an _activated value of false, then there is nothing to
1.254 +// do for safepoint and allocation checking, but there may still be
1.255 +// something to do for the underlying No_GC_Verifier object.
1.256 +
1.257 +class Pause_No_Safepoint_Verifier : public Pause_No_GC_Verifier {
1.258 + private:
1.259 + No_Safepoint_Verifier * _nsv;
1.260 +
1.261 + public:
1.262 +#ifdef ASSERT
1.263 + Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
1.264 + : Pause_No_GC_Verifier(nsv) {
1.265 +
1.266 + _nsv = nsv;
1.267 + if (_nsv->_activated) {
1.268 + _nsv->_thread->_allow_allocation_count--;
1.269 + _nsv->_thread->_allow_safepoint_count--;
1.270 + }
1.271 + }
1.272 +
1.273 + ~Pause_No_Safepoint_Verifier() {
1.274 + if (_nsv->_activated) {
1.275 + _nsv->_thread->_allow_allocation_count++;
1.276 + _nsv->_thread->_allow_safepoint_count++;
1.277 + }
1.278 + }
1.279 +#else
1.280 + Pause_No_Safepoint_Verifier(No_Safepoint_Verifier * nsv)
1.281 + : Pause_No_GC_Verifier(nsv) {}
1.282 + ~Pause_No_Safepoint_Verifier() {}
1.283 +#endif
1.284 +};
1.285 +
1.286 +// A SkipGCALot object is used to elide the usual effect of gc-a-lot
1.287 +// over a section of execution by a thread. Currently, it's used only to
1.288 +// prevent re-entrant calls to GC.
1.289 +class SkipGCALot : public StackObj {
1.290 + private:
1.291 + bool _saved;
1.292 + Thread* _t;
1.293 +
1.294 + public:
1.295 +#ifdef ASSERT
1.296 + SkipGCALot(Thread* t) : _t(t) {
1.297 + _saved = _t->skip_gcalot();
1.298 + _t->set_skip_gcalot(true);
1.299 + }
1.300 +
1.301 + ~SkipGCALot() {
1.302 + assert(_t->skip_gcalot(), "Save-restore protocol invariant");
1.303 + _t->set_skip_gcalot(_saved);
1.304 + }
1.305 +#else
1.306 + SkipGCALot(Thread* t) { }
1.307 + ~SkipGCALot() { }
1.308 +#endif
1.309 +};
1.310 +
1.311 +// JRT_LEAF currently can be called from either _thread_in_Java or
1.312 +// _thread_in_native mode. In _thread_in_native, it is ok
1.313 +// for another thread to trigger GC. The rest of the JRT_LEAF
1.314 +// rules apply.
1.315 +class JRT_Leaf_Verifier : public No_Safepoint_Verifier {
1.316 + static bool should_verify_GC();
1.317 + public:
1.318 +#ifdef ASSERT
1.319 + JRT_Leaf_Verifier();
1.320 + ~JRT_Leaf_Verifier();
1.321 +#else
1.322 + JRT_Leaf_Verifier() {}
1.323 + ~JRT_Leaf_Verifier() {}
1.324 +#endif
1.325 +};
1.326 +
1.327 +// A No_Alloc_Verifier object can be placed in methods where one assumes that
1.328 +// no allocation will occur. The destructor will verify this property
1.329 +// unless the constructor is called with argument false (not activated).
1.330 +//
1.331 +// The check will only be done in debug mode and if activated.
1.332 +// Note: this only makes sense at safepoints (otherwise, other threads may
1.333 +// allocate concurrently.)
1.334 +
1.335 +class No_Alloc_Verifier : public StackObj {
1.336 + private:
1.337 + bool _activated;
1.338 +
1.339 + public:
1.340 +#ifdef ASSERT
1.341 + No_Alloc_Verifier(bool activated = true) {
1.342 + _activated = activated;
1.343 + if (_activated) Thread::current()->_allow_allocation_count++;
1.344 + }
1.345 +
1.346 + ~No_Alloc_Verifier() {
1.347 + if (_activated) Thread::current()->_allow_allocation_count--;
1.348 + }
1.349 +#else
1.350 + No_Alloc_Verifier(bool activated = true) {}
1.351 + ~No_Alloc_Verifier() {}
1.352 +#endif
1.353 +};
1.354 +
1.355 +#endif // SHARE_VM_MEMORY_GCLOCKER_HPP
