1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp Wed Apr 27 01:25:04 2016 +0800
1.3 @@ -0,0 +1,281 @@
1.4 +/*
1.5 + * Copyright (c) 2001, 2014, 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_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
1.29 +#define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
1.30 +
1.31 +#include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
1.32 +#include "gc_implementation/shared/concurrentGCThread.hpp"
1.33 +#include "runtime/thread.inline.hpp"
1.34 +
1.35 +class ConcurrentMarkSweepGeneration;
1.36 +class CMSCollector;
1.37 +
1.38 +// The Concurrent Mark Sweep GC Thread
1.39 +class ConcurrentMarkSweepThread: public ConcurrentGCThread {
1.40 + friend class VMStructs;
1.41 + friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship
1.42 + friend class CMSCollector;
1.43 + public:
1.44 + virtual void run();
1.45 +
1.46 + private:
1.47 + static ConcurrentMarkSweepThread* _cmst;
1.48 + static CMSCollector* _collector;
1.49 + static SurrogateLockerThread* _slt;
1.50 + static SurrogateLockerThread::SLT_msg_type _sltBuffer;
1.51 + static Monitor* _sltMonitor;
1.52 +
1.53 + static bool _should_terminate;
1.54 +
1.55 + enum CMS_flag_type {
1.56 + CMS_nil = NoBits,
1.57 + CMS_cms_wants_token = nth_bit(0),
1.58 + CMS_cms_has_token = nth_bit(1),
1.59 + CMS_vm_wants_token = nth_bit(2),
1.60 + CMS_vm_has_token = nth_bit(3)
1.61 + };
1.62 +
1.63 + static int _CMS_flag;
1.64 +
1.65 + static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
1.66 + static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
1.67 + static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
1.68 + void sleepBeforeNextCycle();
1.69 +
1.70 + // CMS thread should yield for a young gen collection, direct allocation,
1.71 + // and iCMS activity.
1.72 + static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
1.73 + static volatile jint _pending_yields;
1.74 + static volatile jint _pending_decrements; // decrements to _pending_yields
1.75 + static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
1.76 +
1.77 + // Tracing messages, enabled by CMSTraceThreadState.
1.78 + static inline void trace_state(const char* desc);
1.79 +
1.80 + static volatile int _icms_disabled; // a counter to track #iCMS disable & enable
1.81 + static volatile bool _should_run; // iCMS may run
1.82 + static volatile bool _should_stop; // iCMS should stop
1.83 +
1.84 + // debugging
1.85 + void verify_ok_to_terminate() const PRODUCT_RETURN;
1.86 +
1.87 + public:
1.88 + // Constructor
1.89 + ConcurrentMarkSweepThread(CMSCollector* collector);
1.90 +
1.91 + static void makeSurrogateLockerThread(TRAPS);
1.92 + static SurrogateLockerThread* slt() { return _slt; }
1.93 +
1.94 + // Tester
1.95 + bool is_ConcurrentGC_thread() const { return true; }
1.96 +
1.97 + static void threads_do(ThreadClosure* tc);
1.98 +
1.99 + // Printing
1.100 + void print_on(outputStream* st) const;
1.101 + void print() const { print_on(tty); }
1.102 + static void print_all_on(outputStream* st);
1.103 + static void print_all() { print_all_on(tty); }
1.104 +
1.105 + // Returns the CMS Thread
1.106 + static ConcurrentMarkSweepThread* cmst() { return _cmst; }
1.107 + static CMSCollector* collector() { return _collector; }
1.108 +
1.109 + // Create and start the CMS Thread, or stop it on shutdown
1.110 + static ConcurrentMarkSweepThread* start(CMSCollector* collector);
1.111 + static void stop();
1.112 + static bool should_terminate() { return _should_terminate; }
1.113 +
1.114 + // Synchronization using CMS token
1.115 + static void synchronize(bool is_cms_thread);
1.116 + static void desynchronize(bool is_cms_thread);
1.117 + static bool vm_thread_has_cms_token() {
1.118 + return CMS_flag_is_set(CMS_vm_has_token);
1.119 + }
1.120 + static bool cms_thread_has_cms_token() {
1.121 + return CMS_flag_is_set(CMS_cms_has_token);
1.122 + }
1.123 + static bool vm_thread_wants_cms_token() {
1.124 + return CMS_flag_is_set(CMS_vm_wants_token);
1.125 + }
1.126 + static bool cms_thread_wants_cms_token() {
1.127 + return CMS_flag_is_set(CMS_cms_wants_token);
1.128 + }
1.129 +
1.130 + // Wait on CMS lock until the next synchronous GC
1.131 + // or given timeout, whichever is earlier. A timeout value
1.132 + // of 0 indicates that there is no upper bound on the wait time.
1.133 + // A concurrent full gc request terminates the wait.
1.134 + void wait_on_cms_lock(long t_millis);
1.135 +
1.136 + // Wait on CMS lock until the next synchronous GC
1.137 + // or given timeout, whichever is earlier. A timeout value
1.138 + // of 0 indicates that there is no upper bound on the wait time.
1.139 + // A concurrent full gc request terminates the wait.
1.140 + void wait_on_cms_lock_for_scavenge(long t_millis);
1.141 +
1.142 + // The CMS thread will yield during the work portion of its cycle
1.143 + // only when requested to. Both synchronous and asychronous requests
1.144 + // are provided:
1.145 + // (1) A synchronous request is used for young gen collections and
1.146 + // for direct allocations. The requesting thread increments
1.147 + // _pending_yields at the beginning of an operation, and decrements
1.148 + // _pending_yields when that operation is completed.
1.149 + // In turn, the CMS thread yields when _pending_yields is positive,
1.150 + // and continues to yield until the value reverts to 0.
1.151 + // (2) An asynchronous request, on the other hand, is used by iCMS
1.152 + // for the stop_icms() operation. A single yield satisfies all of
1.153 + // the outstanding asynch yield requests, of which there may
1.154 + // occasionally be several in close succession. To accomplish
1.155 + // this, an asynch-requesting thread atomically increments both
1.156 + // _pending_yields and _pending_decrements. An asynchr requesting
1.157 + // thread does not wait and "acknowledge" completion of an operation
1.158 + // and deregister the request, like the synchronous version described
1.159 + // above does. In turn, after yielding, the CMS thread decrements both
1.160 + // _pending_yields and _pending_decrements by the value seen in
1.161 + // _pending_decrements before the decrement.
1.162 + // NOTE: The above scheme is isomorphic to having two request counters,
1.163 + // one for async requests and one for sync requests, and for the CMS thread
1.164 + // to check the sum of the two counters to decide whether it should yield
1.165 + // and to clear only the async counter when it yields. However, it turns out
1.166 + // to be more efficient for CMS code to just check a single counter
1.167 + // _pending_yields that holds the sum (of both sync and async requests), and
1.168 + // a second counter _pending_decrements that only holds the async requests,
1.169 + // for greater efficiency, since in a typical CMS run, there are many more
1.170 + // pontential (i.e. static) yield points than there are actual
1.171 + // (i.e. dynamic) yields because of requests, which are few and far between.
1.172 + //
1.173 + // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
1.174 + // we cannot easily test that invariant, since the counters are manipulated via
1.175 + // atomic instructions without explicit locking and we cannot read
1.176 + // the two counters atomically together: one suggestion is to
1.177 + // use (for example) 16-bit counters so as to be able to read the
1.178 + // two counters atomically even on 32-bit platforms. Notice that
1.179 + // the second assert in acknowledge_yield_request() below does indeed
1.180 + // check a form of the above invariant, albeit indirectly.
1.181 +
1.182 + static void increment_pending_yields() {
1.183 + Atomic::inc(&_pending_yields);
1.184 + assert(_pending_yields >= 0, "can't be negative");
1.185 + }
1.186 + static void decrement_pending_yields() {
1.187 + Atomic::dec(&_pending_yields);
1.188 + assert(_pending_yields >= 0, "can't be negative");
1.189 + }
1.190 + static void asynchronous_yield_request() {
1.191 + assert(CMSIncrementalMode, "Currently only used w/iCMS");
1.192 + increment_pending_yields();
1.193 + Atomic::inc(&_pending_decrements);
1.194 + assert(_pending_decrements >= 0, "can't be negative");
1.195 + }
1.196 + static void acknowledge_yield_request() {
1.197 + jint decrement = _pending_decrements;
1.198 + if (decrement > 0) {
1.199 + assert(CMSIncrementalMode, "Currently only used w/iCMS");
1.200 + // Order important to preserve: _pending_yields >= _pending_decrements
1.201 + Atomic::add(-decrement, &_pending_decrements);
1.202 + Atomic::add(-decrement, &_pending_yields);
1.203 + assert(_pending_decrements >= 0, "can't be negative");
1.204 + assert(_pending_yields >= 0, "can't be negative");
1.205 + }
1.206 + }
1.207 + static bool should_yield() { return _pending_yields > 0; }
1.208 +
1.209 + // CMS incremental mode.
1.210 + static void start_icms(); // notify thread to start a quantum of work
1.211 + static void stop_icms(); // request thread to stop working
1.212 + void icms_wait(); // if asked to stop, wait until notified to start
1.213 +
1.214 + // Incremental mode is enabled globally by the flag CMSIncrementalMode. It
1.215 + // must also be enabled/disabled dynamically to allow foreground collections.
1.216 +#define ICMS_ENABLING_ASSERT \
1.217 + assert((CMSIncrementalMode && _icms_disabled >= 0) || \
1.218 + (!CMSIncrementalMode && _icms_disabled <= 0), "Error")
1.219 +
1.220 + static inline void enable_icms() {
1.221 + ICMS_ENABLING_ASSERT;
1.222 + Atomic::dec(&_icms_disabled);
1.223 + }
1.224 + static inline void disable_icms() {
1.225 + ICMS_ENABLING_ASSERT;
1.226 + Atomic::inc(&_icms_disabled);
1.227 + }
1.228 + static inline bool icms_is_disabled() {
1.229 + ICMS_ENABLING_ASSERT;
1.230 + return _icms_disabled > 0;
1.231 + }
1.232 + static inline bool icms_is_enabled() {
1.233 + return !icms_is_disabled();
1.234 + }
1.235 +};
1.236 +
1.237 +inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
1.238 + if (CMSTraceThreadState) {
1.239 + char buf[128];
1.240 + TimeStamp& ts = gclog_or_tty->time_stamp();
1.241 + if (!ts.is_updated()) {
1.242 + ts.update();
1.243 + }
1.244 + jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ",
1.245 + ts.seconds(), desc);
1.246 + buf[sizeof(buf) - 1] = '\0';
1.247 + gclog_or_tty->print("%s", buf);
1.248 + }
1.249 +}
1.250 +
1.251 +// For scoped increment/decrement of (synchronous) yield requests
1.252 +class CMSSynchronousYieldRequest: public StackObj {
1.253 + public:
1.254 + CMSSynchronousYieldRequest() {
1.255 + ConcurrentMarkSweepThread::increment_pending_yields();
1.256 + }
1.257 + ~CMSSynchronousYieldRequest() {
1.258 + ConcurrentMarkSweepThread::decrement_pending_yields();
1.259 + }
1.260 +};
1.261 +
1.262 +// Used to emit a warning in case of unexpectedly excessive
1.263 +// looping (in "apparently endless loops") in CMS code.
1.264 +class CMSLoopCountWarn: public StackObj {
1.265 + private:
1.266 + const char* _src;
1.267 + const char* _msg;
1.268 + const intx _threshold;
1.269 + intx _ticks;
1.270 +
1.271 + public:
1.272 + inline CMSLoopCountWarn(const char* src, const char* msg,
1.273 + const intx threshold) :
1.274 + _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
1.275 +
1.276 + inline void tick() {
1.277 + _ticks++;
1.278 + if (CMSLoopWarn && _ticks % _threshold == 0) {
1.279 + warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
1.280 + }
1.281 + }
1.282 +};
1.283 +
1.284 +#endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
