--- /dev/null Thu Jan 01 00:00:00 1970 +0000
+++ b/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,229 @@
+/*
+ * Copyright 2001-2006 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ *
+ */
+
+class ConcurrentMarkSweepGeneration;
+class CMSCollector;
+
+// The Concurrent Mark Sweep GC Thread (could be several in the future).
+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;
+
+ ConcurrentMarkSweepThread* _next;
+
+ 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 bool _icms_enabled; // iCMS enabled?
+ 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.
+ void wait_on_cms_lock(long t); // milliseconds
+
+ // The CMS thread will yield during the work portion of it's cycle
+ // only when requested to. Both synchronous and asychronous requests
+ // are provided. A synchronous request is used for young gen
+ // collections and direct allocations. The requesting thread increments
+ // pending_yields at the beginning of an operation, and decrements it when
+ // the operation is completed. The CMS thread yields when pending_yields
+ // is positive. An asynchronous request is used by iCMS in the stop_icms()
+ // operation. A single yield satisfies the outstanding asynch yield requests.
+ // The requesting thread increments both pending_yields and pending_decrements.
+ // After yielding, the CMS thread decrements both by the amount in
+ // pending_decrements.
+ // 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() 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() {
+ 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) {
+ // 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.
+ static inline void enable_icms() { _icms_enabled = true; }
+ static inline void disable_icms() { _icms_enabled = false; }
+ static inline void set_icms_enabled(bool val) { _icms_enabled = val; }
+ static inline bool icms_enabled() { return _icms_enabled; }
+};
+
+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 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);
+ }
+ }
+};