aoqi@0: /*
aoqi@0:  * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
aoqi@0:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
aoqi@0:  *
aoqi@0:  * This code is free software; you can redistribute it and/or modify it
aoqi@0:  * under the terms of the GNU General Public License version 2 only, as
aoqi@0:  * published by the Free Software Foundation.
aoqi@0:  *
aoqi@0:  * This code is distributed in the hope that it will be useful, but WITHOUT
aoqi@0:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
aoqi@0:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
aoqi@0:  * version 2 for more details (a copy is included in the LICENSE file that
aoqi@0:  * accompanied this code).
aoqi@0:  *
aoqi@0:  * You should have received a copy of the GNU General Public License version
aoqi@0:  * 2 along with this work; if not, write to the Free Software Foundation,
aoqi@0:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
aoqi@0:  *
aoqi@0:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
aoqi@0:  * or visit www.oracle.com if you need additional information or have any
aoqi@0:  * questions.
aoqi@0:  *
aoqi@0:  */
aoqi@0: 
aoqi@0: #ifndef SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
aoqi@0: #define SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP
aoqi@0: 
aoqi@0: #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
aoqi@0: #include "gc_implementation/shared/concurrentGCThread.hpp"
aoqi@0: #include "runtime/thread.inline.hpp"
aoqi@0: 
aoqi@0: class ConcurrentMarkSweepGeneration;
aoqi@0: class CMSCollector;
aoqi@0: 
aoqi@0: // The Concurrent Mark Sweep GC Thread
aoqi@0: class ConcurrentMarkSweepThread: public ConcurrentGCThread {
aoqi@0:   friend class VMStructs;
aoqi@0:   friend class ConcurrentMarkSweepGeneration;   // XXX should remove friendship
aoqi@0:   friend class CMSCollector;
aoqi@0:  public:
aoqi@0:   virtual void run();
aoqi@0: 
aoqi@0:  private:
aoqi@0:   static ConcurrentMarkSweepThread*     _cmst;
aoqi@0:   static CMSCollector*                  _collector;
aoqi@0:   static SurrogateLockerThread*         _slt;
aoqi@0:   static SurrogateLockerThread::SLT_msg_type _sltBuffer;
aoqi@0:   static Monitor*                       _sltMonitor;
aoqi@0: 
aoqi@0:   static bool _should_terminate;
aoqi@0: 
aoqi@0:   enum CMS_flag_type {
aoqi@0:     CMS_nil             = NoBits,
aoqi@0:     CMS_cms_wants_token = nth_bit(0),
aoqi@0:     CMS_cms_has_token   = nth_bit(1),
aoqi@0:     CMS_vm_wants_token  = nth_bit(2),
aoqi@0:     CMS_vm_has_token    = nth_bit(3)
aoqi@0:   };
aoqi@0: 
aoqi@0:   static int _CMS_flag;
aoqi@0: 
aoqi@0:   static bool CMS_flag_is_set(int b)        { return (_CMS_flag & b) != 0;   }
aoqi@0:   static bool set_CMS_flag(int b)           { return (_CMS_flag |= b) != 0;  }
aoqi@0:   static bool clear_CMS_flag(int b)         { return (_CMS_flag &= ~b) != 0; }
aoqi@0:   void sleepBeforeNextCycle();
aoqi@0: 
aoqi@0:   // CMS thread should yield for a young gen collection, direct allocation,
aoqi@0:   // and iCMS activity.
aoqi@0:   static char _pad_1[64 - sizeof(jint)];    // prevent cache-line sharing
aoqi@0:   static volatile jint _pending_yields;
aoqi@0:   static volatile jint _pending_decrements; // decrements to _pending_yields
aoqi@0:   static char _pad_2[64 - sizeof(jint)];    // prevent cache-line sharing
aoqi@0: 
aoqi@0:   // Tracing messages, enabled by CMSTraceThreadState.
aoqi@0:   static inline void trace_state(const char* desc);
aoqi@0: 
aoqi@0:   static volatile int _icms_disabled;   // a counter to track #iCMS disable & enable
aoqi@0:   static volatile bool _should_run;     // iCMS may run
aoqi@0:   static volatile bool _should_stop;    // iCMS should stop
aoqi@0: 
aoqi@0:   // debugging
aoqi@0:   void verify_ok_to_terminate() const PRODUCT_RETURN;
aoqi@0: 
aoqi@0:  public:
aoqi@0:   // Constructor
aoqi@0:   ConcurrentMarkSweepThread(CMSCollector* collector);
aoqi@0: 
aoqi@0:   static void makeSurrogateLockerThread(TRAPS);
aoqi@0:   static SurrogateLockerThread* slt() { return _slt; }
aoqi@0: 
aoqi@0:   // Tester
aoqi@0:   bool is_ConcurrentGC_thread() const { return true;       }
aoqi@0: 
aoqi@0:   static void threads_do(ThreadClosure* tc);
aoqi@0: 
aoqi@0:   // Printing
aoqi@0:   void print_on(outputStream* st) const;
aoqi@0:   void print() const                                  { print_on(tty); }
aoqi@0:   static void print_all_on(outputStream* st);
aoqi@0:   static void print_all()                             { print_all_on(tty); }
aoqi@0: 
aoqi@0:   // Returns the CMS Thread
aoqi@0:   static ConcurrentMarkSweepThread* cmst()    { return _cmst; }
aoqi@0:   static CMSCollector*         collector()    { return _collector;  }
aoqi@0: 
aoqi@0:   // Create and start the CMS Thread, or stop it on shutdown
aoqi@0:   static ConcurrentMarkSweepThread* start(CMSCollector* collector);
aoqi@0:   static void stop();
aoqi@0:   static bool should_terminate() { return _should_terminate; }
aoqi@0: 
aoqi@0:   // Synchronization using CMS token
aoqi@0:   static void synchronize(bool is_cms_thread);
aoqi@0:   static void desynchronize(bool is_cms_thread);
aoqi@0:   static bool vm_thread_has_cms_token() {
aoqi@0:     return CMS_flag_is_set(CMS_vm_has_token);
aoqi@0:   }
aoqi@0:   static bool cms_thread_has_cms_token() {
aoqi@0:     return CMS_flag_is_set(CMS_cms_has_token);
aoqi@0:   }
aoqi@0:   static bool vm_thread_wants_cms_token() {
aoqi@0:     return CMS_flag_is_set(CMS_vm_wants_token);
aoqi@0:   }
aoqi@0:   static bool cms_thread_wants_cms_token() {
aoqi@0:     return CMS_flag_is_set(CMS_cms_wants_token);
aoqi@0:   }
aoqi@0: 
aoqi@0:   // Wait on CMS lock until the next synchronous GC
aoqi@0:   // or given timeout, whichever is earlier. A timeout value
aoqi@0:   // of 0 indicates that there is no upper bound on the wait time.
aoqi@0:   // A concurrent full gc request terminates the wait.
aoqi@0:   void wait_on_cms_lock(long t_millis);
aoqi@0: 
aoqi@0:   // Wait on CMS lock until the next synchronous GC
aoqi@0:   // or given timeout, whichever is earlier. A timeout value
aoqi@0:   // of 0 indicates that there is no upper bound on the wait time.
aoqi@0:   // A concurrent full gc request terminates the wait.
aoqi@0:   void wait_on_cms_lock_for_scavenge(long t_millis);
aoqi@0: 
aoqi@0:   // The CMS thread will yield during the work portion of its cycle
aoqi@0:   // only when requested to.  Both synchronous and asychronous requests
aoqi@0:   // are provided:
aoqi@0:   // (1) A synchronous request is used for young gen collections and
aoqi@0:   //     for direct allocations.  The requesting thread increments
aoqi@0:   //     _pending_yields at the beginning of an operation, and decrements
aoqi@0:   //     _pending_yields when that operation is completed.
aoqi@0:   //     In turn, the CMS thread yields when _pending_yields is positive,
aoqi@0:   //     and continues to yield until the value reverts to 0.
aoqi@0:   // (2) An asynchronous request, on the other hand, is used by iCMS
aoqi@0:   //     for the stop_icms() operation. A single yield satisfies all of
aoqi@0:   //     the outstanding asynch yield requests, of which there may
aoqi@0:   //     occasionally be several in close succession. To accomplish
aoqi@0:   //     this, an asynch-requesting thread atomically increments both
aoqi@0:   //     _pending_yields and _pending_decrements. An asynchr requesting
aoqi@0:   //     thread does not wait and "acknowledge" completion of an operation
aoqi@0:   //     and deregister the request, like the synchronous version described
aoqi@0:   //     above does. In turn, after yielding, the CMS thread decrements both
aoqi@0:   //     _pending_yields and _pending_decrements by the value seen in
aoqi@0:   //     _pending_decrements before the decrement.
aoqi@0:   //  NOTE: The above scheme is isomorphic to having two request counters,
aoqi@0:   //  one for async requests and one for sync requests, and for the CMS thread
aoqi@0:   //  to check the sum of the two counters to decide whether it should yield
aoqi@0:   //  and to clear only the async counter when it yields. However, it turns out
aoqi@0:   //  to be more efficient for CMS code to just check a single counter
aoqi@0:   //  _pending_yields that holds the sum (of both sync and async requests), and
aoqi@0:   //  a second counter _pending_decrements that only holds the async requests,
aoqi@0:   //  for greater efficiency, since in a typical CMS run, there are many more
aoqi@0:   //  pontential (i.e. static) yield points than there are actual
aoqi@0:   //  (i.e. dynamic) yields because of requests, which are few and far between.
aoqi@0:   //
aoqi@0:   // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
aoqi@0:   // we cannot easily test that invariant, since the counters are manipulated via
aoqi@0:   // atomic instructions without explicit locking and we cannot read
aoqi@0:   // the two counters atomically together: one suggestion is to
aoqi@0:   // use (for example) 16-bit counters so as to be able to read the
aoqi@0:   // two counters atomically even on 32-bit platforms. Notice that
aoqi@0:   // the second assert in acknowledge_yield_request() below does indeed
aoqi@0:   // check a form of the above invariant, albeit indirectly.
aoqi@0: 
aoqi@0:   static void increment_pending_yields()   {
aoqi@0:     Atomic::inc(&_pending_yields);
aoqi@0:     assert(_pending_yields >= 0, "can't be negative");
aoqi@0:   }
aoqi@0:   static void decrement_pending_yields()   {
aoqi@0:     Atomic::dec(&_pending_yields);
aoqi@0:     assert(_pending_yields >= 0, "can't be negative");
aoqi@0:   }
aoqi@0:   static void asynchronous_yield_request() {
aoqi@0:     assert(CMSIncrementalMode, "Currently only used w/iCMS");
aoqi@0:     increment_pending_yields();
aoqi@0:     Atomic::inc(&_pending_decrements);
aoqi@0:     assert(_pending_decrements >= 0, "can't be negative");
aoqi@0:   }
aoqi@0:   static void acknowledge_yield_request() {
aoqi@0:     jint decrement = _pending_decrements;
aoqi@0:     if (decrement > 0) {
aoqi@0:       assert(CMSIncrementalMode, "Currently only used w/iCMS");
aoqi@0:       // Order important to preserve: _pending_yields >= _pending_decrements
aoqi@0:       Atomic::add(-decrement, &_pending_decrements);
aoqi@0:       Atomic::add(-decrement, &_pending_yields);
aoqi@0:       assert(_pending_decrements >= 0, "can't be negative");
aoqi@0:       assert(_pending_yields >= 0, "can't be negative");
aoqi@0:     }
aoqi@0:   }
aoqi@0:   static bool should_yield()   { return _pending_yields > 0; }
aoqi@0: 
aoqi@0:   // CMS incremental mode.
aoqi@0:   static void start_icms(); // notify thread to start a quantum of work
aoqi@0:   static void stop_icms();  // request thread to stop working
aoqi@0:   void icms_wait();         // if asked to stop, wait until notified to start
aoqi@0: 
aoqi@0:   // Incremental mode is enabled globally by the flag CMSIncrementalMode.  It
aoqi@0:   // must also be enabled/disabled dynamically to allow foreground collections.
aoqi@0: #define ICMS_ENABLING_ASSERT                                                      \
aoqi@0:           assert((CMSIncrementalMode  && _icms_disabled >= 0) ||                  \
aoqi@0:                  (!CMSIncrementalMode && _icms_disabled <= 0), "Error")
aoqi@0: 
aoqi@0:   static inline void enable_icms() {
aoqi@0:     ICMS_ENABLING_ASSERT;
aoqi@0:     Atomic::dec(&_icms_disabled);
aoqi@0:   }
aoqi@0:   static inline void disable_icms() {
aoqi@0:    ICMS_ENABLING_ASSERT;
aoqi@0:    Atomic::inc(&_icms_disabled);
aoqi@0:   }
aoqi@0:   static inline bool icms_is_disabled() {
aoqi@0:    ICMS_ENABLING_ASSERT;
aoqi@0:    return _icms_disabled > 0;
aoqi@0:   }
aoqi@0:   static inline bool icms_is_enabled() {
aoqi@0:    return !icms_is_disabled();
aoqi@0:   }
aoqi@0: };
aoqi@0: 
aoqi@0: inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
aoqi@0:   if (CMSTraceThreadState) {
aoqi@0:     char buf[128];
aoqi@0:     TimeStamp& ts = gclog_or_tty->time_stamp();
aoqi@0:     if (!ts.is_updated()) {
aoqi@0:       ts.update();
aoqi@0:     }
aoqi@0:     jio_snprintf(buf, sizeof(buf), " [%.3f:  CMSThread %s] ",
aoqi@0:                  ts.seconds(), desc);
aoqi@0:     buf[sizeof(buf) - 1] = '\0';
aoqi@0:     gclog_or_tty->print("%s", buf);
aoqi@0:   }
aoqi@0: }
aoqi@0: 
aoqi@0: // For scoped increment/decrement of (synchronous) yield requests
aoqi@0: class CMSSynchronousYieldRequest: public StackObj {
aoqi@0:  public:
aoqi@0:   CMSSynchronousYieldRequest() {
aoqi@0:     ConcurrentMarkSweepThread::increment_pending_yields();
aoqi@0:   }
aoqi@0:   ~CMSSynchronousYieldRequest() {
aoqi@0:     ConcurrentMarkSweepThread::decrement_pending_yields();
aoqi@0:   }
aoqi@0: };
aoqi@0: 
aoqi@0: // Used to emit a warning in case of unexpectedly excessive
aoqi@0: // looping (in "apparently endless loops") in CMS code.
aoqi@0: class CMSLoopCountWarn: public StackObj {
aoqi@0:  private:
aoqi@0:   const char* _src;
aoqi@0:   const char* _msg;
aoqi@0:   const intx  _threshold;
aoqi@0:   intx        _ticks;
aoqi@0: 
aoqi@0:  public:
aoqi@0:   inline CMSLoopCountWarn(const char* src, const char* msg,
aoqi@0:                           const intx threshold) :
aoqi@0:     _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
aoqi@0: 
aoqi@0:   inline void tick() {
aoqi@0:     _ticks++;
aoqi@0:     if (CMSLoopWarn && _ticks % _threshold == 0) {
aoqi@0:       warning("%s has looped " INTX_FORMAT " times %s", _src, _ticks, _msg);
aoqi@0:     }
aoqi@0:   }
aoqi@0: };
aoqi@0: 
aoqi@0: #endif // SHARE_VM_GC_IMPLEMENTATION_CONCURRENTMARKSWEEP_CONCURRENTMARKSWEEPTHREAD_HPP