| /* |
| * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| * |
| */ |
| |
| #ifndef SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP |
| #define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP |
| |
| #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp" |
| #include "gc_implementation/shared/concurrentGCThread.hpp" |
| #include "runtime/thread.inline.hpp" |
| |
| class ConcurrentMarkSweepGeneration; |
| class CMSCollector; |
| |
| // The Concurrent Mark Sweep GC Thread |
| class ConcurrentMarkSweepThread: public ConcurrentGCThread { |
| friend class VMStructs; |
| friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship |
| friend class CMSCollector; |
| public: |
| virtual void run(); |
| |
| private: |
| static ConcurrentMarkSweepThread* _cmst; |
| static CMSCollector* _collector; |
| static SurrogateLockerThread* _slt; |
| static SurrogateLockerThread::SLT_msg_type _sltBuffer; |
| static Monitor* _sltMonitor; |
| |
| static bool _should_terminate; |
| |
| enum CMS_flag_type { |
| CMS_nil = NoBits, |
| CMS_cms_wants_token = nth_bit(0), |
| CMS_cms_has_token = nth_bit(1), |
| CMS_vm_wants_token = nth_bit(2), |
| CMS_vm_has_token = nth_bit(3) |
| }; |
| |
| static int _CMS_flag; |
| |
| static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; } |
| static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; } |
| static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; } |
| void sleepBeforeNextCycle(); |
| |
| // CMS thread should yield for a young gen collection, direct allocation, |
| // and iCMS activity. |
| static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing |
| static volatile jint _pending_yields; |
| static volatile jint _pending_decrements; // decrements to _pending_yields |
| static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing |
| |
| // Tracing messages, enabled by CMSTraceThreadState. |
| static inline void trace_state(const char* desc); |
| |
| static volatile int _icms_disabled; // a counter to track #iCMS disable & enable |
| static volatile bool _should_run; // iCMS may run |
| static volatile bool _should_stop; // iCMS should stop |
| |
| // debugging |
| void verify_ok_to_terminate() const PRODUCT_RETURN; |
| |
| public: |
| // Constructor |
| ConcurrentMarkSweepThread(CMSCollector* collector); |
| |
| static void makeSurrogateLockerThread(TRAPS); |
| static SurrogateLockerThread* slt() { return _slt; } |
| |
| // Tester |
| bool is_ConcurrentGC_thread() const { return true; } |
| |
| static void threads_do(ThreadClosure* tc); |
| |
| // Printing |
| void print_on(outputStream* st) const; |
| void print() const { print_on(tty); } |
| static void print_all_on(outputStream* st); |
| static void print_all() { print_all_on(tty); } |
| |
| // Returns the CMS Thread |
| static ConcurrentMarkSweepThread* cmst() { return _cmst; } |
| static CMSCollector* collector() { return _collector; } |
| |
| // Create and start the CMS Thread, or stop it on shutdown |
| static ConcurrentMarkSweepThread* start(CMSCollector* collector); |
| static void stop(); |
| static bool should_terminate() { return _should_terminate; } |
| |
| // Synchronization using CMS token |
| static void synchronize(bool is_cms_thread); |
| static void desynchronize(bool is_cms_thread); |
| static bool vm_thread_has_cms_token() { |
| return CMS_flag_is_set(CMS_vm_has_token); |
| } |
| static bool cms_thread_has_cms_token() { |
| return CMS_flag_is_set(CMS_cms_has_token); |
| } |
| static bool vm_thread_wants_cms_token() { |
| return CMS_flag_is_set(CMS_vm_wants_token); |
| } |
| static bool cms_thread_wants_cms_token() { |
| return CMS_flag_is_set(CMS_cms_wants_token); |
| } |
| |
| // Wait on CMS lock until the next synchronous GC |
| // or given timeout, whichever is earlier. A timeout value |
| // of 0 indicates that there is no upper bound on the wait time. |
| // A concurrent full gc request terminates the wait. |
| void wait_on_cms_lock(long t_millis); |
| |
| // Wait on CMS lock until the next synchronous GC |
| // or given timeout, whichever is earlier. A timeout value |
| // of 0 indicates that there is no upper bound on the wait time. |
| // A concurrent full gc request terminates the wait. |
| void wait_on_cms_lock_for_scavenge(long t_millis); |
| |
| // The CMS thread will yield during the work portion of its cycle |
| // only when requested to. Both synchronous and asychronous requests |
| // are provided: |
| // (1) A synchronous request is used for young gen collections and |
| // for direct allocations. The requesting thread increments |
| // _pending_yields at the beginning of an operation, and decrements |
| // _pending_yields when that operation is completed. |
| // In turn, the CMS thread yields when _pending_yields is positive, |
| // and continues to yield until the value reverts to 0. |
| // (2) An asynchronous request, on the other hand, is used by iCMS |
| // for the stop_icms() operation. A single yield satisfies all of |
| // the outstanding asynch yield requests, of which there may |
| // occasionally be several in close succession. To accomplish |
| // this, an asynch-requesting thread atomically increments both |
| // _pending_yields and _pending_decrements. An asynchr requesting |
| // thread does not wait and "acknowledge" completion of an operation |
| // and deregister the request, like the synchronous version described |
| // above does. In turn, after yielding, the CMS thread decrements both |
| // _pending_yields and _pending_decrements by the value seen in |
| // _pending_decrements before the decrement. |
| // NOTE: The above scheme is isomorphic to having two request counters, |
| // one for async requests and one for sync requests, and for the CMS thread |
| // to check the sum of the two counters to decide whether it should yield |
| // and to clear only the async counter when it yields. However, it turns out |
| // to be more efficient for CMS code to just check a single counter |
| // _pending_yields that holds the sum (of both sync and async requests), and |
| // a second counter _pending_decrements that only holds the async requests, |
| // for greater efficiency, since in a typical CMS run, there are many more |
| // potential (i.e. static) yield points than there are actual |
| // (i.e. dynamic) yields because of requests, which are few and far between. |
| // |
| // Note that, while "_pending_yields >= _pending_decrements" is an invariant, |
| // we cannot easily test that invariant, since the counters are manipulated via |
| // atomic instructions without explicit locking and we cannot read |
| // the two counters atomically together: one suggestion is to |
| // use (for example) 16-bit counters so as to be able to read the |
| // two counters atomically even on 32-bit platforms. Notice that |
| // the second assert in acknowledge_yield_request() below does indeed |
| // check a form of the above invariant, albeit indirectly. |
| |
| static void increment_pending_yields() { |
| Atomic::inc(&_pending_yields); |
| assert(_pending_yields >= 0, "can't be negative"); |
| } |
| static void decrement_pending_yields() { |
| Atomic::dec(&_pending_yields); |
| assert(_pending_yields >= 0, "can't be negative"); |
| } |
| static void asynchronous_yield_request() { |
| assert(CMSIncrementalMode, "Currently only used w/iCMS"); |
| increment_pending_yields(); |
| Atomic::inc(&_pending_decrements); |
| assert(_pending_decrements >= 0, "can't be negative"); |
| } |
| static void acknowledge_yield_request() { |
| jint decrement = _pending_decrements; |
| if (decrement > 0) { |
| assert(CMSIncrementalMode, "Currently only used w/iCMS"); |
| // Order important to preserve: _pending_yields >= _pending_decrements |
| Atomic::add(-decrement, &_pending_decrements); |
| Atomic::add(-decrement, &_pending_yields); |
| assert(_pending_decrements >= 0, "can't be negative"); |
| assert(_pending_yields >= 0, "can't be negative"); |
| } |
| } |
| static bool should_yield() { return _pending_yields > 0; } |
| |
| // CMS incremental mode. |
| static void start_icms(); // notify thread to start a quantum of work |
| static void stop_icms(); // request thread to stop working |
| void icms_wait(); // if asked to stop, wait until notified to start |
| |
| // Incremental mode is enabled globally by the flag CMSIncrementalMode. It |
| // must also be enabled/disabled dynamically to allow foreground collections. |
| #define ICMS_ENABLING_ASSERT \ |
| assert((CMSIncrementalMode && _icms_disabled >= 0) || \ |
| (!CMSIncrementalMode && _icms_disabled <= 0), "Error") |
| |
| static inline void enable_icms() { |
| ICMS_ENABLING_ASSERT; |
| Atomic::dec(&_icms_disabled); |
| } |
| static inline void disable_icms() { |
| ICMS_ENABLING_ASSERT; |
| Atomic::inc(&_icms_disabled); |
| } |
| static inline bool icms_is_disabled() { |
| ICMS_ENABLING_ASSERT; |
| return _icms_disabled > 0; |
| } |
| static inline bool icms_is_enabled() { |
| return !icms_is_disabled(); |
| } |
| }; |
| |
| inline void ConcurrentMarkSweepThread::trace_state(const char* desc) { |
| if (CMSTraceThreadState) { |
| char buf[128]; |
| TimeStamp& ts = gclog_or_tty->time_stamp(); |
| if (!ts.is_updated()) { |
| ts.update(); |
| } |
| jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ", |
| ts.seconds(), desc); |
| buf[sizeof(buf) - 1] = '\0'; |
| gclog_or_tty->print(buf); |
| } |
| } |
| |
| // For scoped increment/decrement of (synchronous) yield requests |
| class CMSSynchronousYieldRequest: public StackObj { |
| public: |
| CMSSynchronousYieldRequest() { |
| ConcurrentMarkSweepThread::increment_pending_yields(); |
| } |
| ~CMSSynchronousYieldRequest() { |
| ConcurrentMarkSweepThread::decrement_pending_yields(); |
| } |
| }; |
| |
| // Used to emit a warning in case of unexpectedly excessive |
| // looping (in "apparently endless loops") in CMS code. |
| class CMSLoopCountWarn: public StackObj { |
| private: |
| const char* _src; |
| const char* _msg; |
| const intx _threshold; |
| intx _ticks; |
| |
| public: |
| inline CMSLoopCountWarn(const char* src, const char* msg, |
| const intx threshold) : |
| _src(src), _msg(msg), _threshold(threshold), _ticks(0) { } |
| |
| inline void tick() { |
| _ticks++; |
| if (CMSLoopWarn && _ticks % _threshold == 0) { |
| warning("%s has looped %d times %s", _src, _ticks, _msg); |
| } |
| } |
| }; |
| |
| #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP |