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hotspot/src/share/vm/runtime/safepoint.hpp

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+/*
+ * Copyright 1997-2007 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.
+ *
+ */
+
+//
+// Safepoint synchronization
+////
+// The VMThread or CMS_thread uses the SafepointSynchronize::begin/end
+// methods to enter/exit a safepoint region. The begin method will roll
+// all JavaThreads forward to a safepoint.
+//
+// JavaThreads must use the ThreadSafepointState abstraction (defined in
+// thread.hpp) to indicate that that they are at a safepoint.
+//
+// The Mutex/Condition variable and ObjectLocker classes calls the enter/
+// exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/
+// exit points *must* be at a safepoint.
+
+
+class ThreadSafepointState;
+class SnippetCache;
+class nmethod;
+
+//
+// Implements roll-forward to safepoint (safepoint synchronization)
+//
+class SafepointSynchronize : AllStatic {
+ public:
+  enum SynchronizeState {
+      _not_synchronized = 0,                   // Threads not synchronized at a safepoint
+                                               // Keep this value 0. See the coment in do_call_back()
+      _synchronizing    = 1,                   // Synchronizing in progress
+      _synchronized     = 2                    // All Java threads are stopped at a safepoint. Only VM thread is running
+  };
+
+  enum SafepointingThread {
+      _null_thread  = 0,
+      _vm_thread    = 1,
+      _other_thread = 2
+  };
+
+  enum SafepointTimeoutReason {
+    _spinning_timeout = 0,
+    _blocking_timeout = 1
+  };
+
+  typedef struct {
+    int    _vmop_type;                         // type of VM operation triggers the safepoint
+    int    _nof_total_threads;                 // total number of Java threads
+    int    _nof_initial_running_threads;       // total number of initially seen running threads
+    int    _nof_threads_wait_to_block;         // total number of threads waiting for to block
+    bool   _page_armed;                        // true if polling page is armed, false otherwise
+    int    _nof_threads_hit_page_trap;         // total number of threads hitting the page trap
+    jlong  _time_to_spin;                      // total time in millis spent in spinning
+    jlong  _time_to_wait_to_block;             // total time in millis spent in waiting for to block
+    jlong  _time_to_sync;                      // total time in millis spent in getting to _synchronized
+    jlong  _time_to_exec_vmop;                 // total time in millis spent in vm operation itself
+    jlong  _time_elapsed_since_last_safepoint; // time elasped since last safepoint
+  } SafepointStats;
+
+ private:
+  static volatile SynchronizeState _state;     // Threads might read this flag directly, without acquireing the Threads_lock
+  static volatile int _waiting_to_block;       // No. of threads we are waiting for to block.
+
+  // This counter is used for fast versions of jni_Get<Primitive>Field.
+  // An even value means there is no ongoing safepoint operations.
+  // The counter is incremented ONLY at the beginning and end of each
+  // safepoint. The fact that Threads_lock is held throughout each pair of
+  // increments (at the beginning and end of each safepoint) guarantees
+  // race freedom.
+public:
+  static volatile int _safepoint_counter;
+private:
+
+  static jlong   _last_safepoint;      // Time of last safepoint
+
+  // statistics
+  static SafepointStats*  _safepoint_stats;     // array of SafepointStats struct
+  static int              _cur_stat_index;      // current index to the above array
+  static julong           _safepoint_reasons[]; // safepoint count for each VM op
+  static julong           _coalesced_vmop_count;// coalesced vmop count
+  static jlong            _max_sync_time;       // maximum sync time in nanos
+
+  static void begin_statistics(int nof_threads, int nof_running);
+  static void update_statistics_on_spin_end();
+  static void update_statistics_on_sync_end(jlong end_time);
+  static void end_statistics(jlong end_time);
+  static void print_statistics();
+  inline static void inc_page_trap_count() {
+    Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);
+  }
+
+  // For debug long safepoint
+  static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);
+
+public:
+
+  // Main entry points
+
+  // Roll all threads forward to safepoint. Must be called by the
+  // VMThread or CMS_thread.
+  static void begin();
+  static void end();                    // Start all suspended threads again...
+
+  static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
+
+  // Query
+  inline static bool is_at_safepoint()   { return _state == _synchronized;  }
+  inline static bool is_synchronizing()  { return _state == _synchronizing;  }
+
+  inline static bool do_call_back() {
+    return (_state != _not_synchronized);
+  }
+
+  // Called when a thread volantary blocks
+  static void   block(JavaThread *thread);
+  static void   signal_thread_at_safepoint()              { _waiting_to_block--; }
+
+  // Exception handling for page polling
+  static void handle_polling_page_exception(JavaThread *thread);
+
+  // VM Thread interface for determining safepoint rate
+  static long last_non_safepoint_interval()               { return os::javaTimeMillis() - _last_safepoint; }
+  static bool is_cleanup_needed();
+  static void do_cleanup_tasks();
+
+  // debugging
+  static void print_state()                                PRODUCT_RETURN;
+  static void safepoint_msg(const char* format, ...)       PRODUCT_RETURN;
+
+  static void deferred_initialize_stat();
+  static void print_stat_on_exit();
+  inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
+
+  static void set_is_at_safepoint()                        { _state = _synchronized; }
+  static void set_is_not_at_safepoint()                    { _state = _not_synchronized; }
+
+  // assembly support
+  static address address_of_state()                        { return (address)&_state; }
+
+  static address safepoint_counter_addr()                  { return (address)&_safepoint_counter; }
+};
+
+// State class for a thread suspended at a safepoint
+class ThreadSafepointState: public CHeapObj {
+ public:
+  // These states are maintained by VM thread while threads are being brought
+  // to a safepoint.  After SafepointSynchronize::end(), they are reset to
+  // _running.
+  enum suspend_type {
+    _running                =  0, // Thread state not yet determined (i.e., not at a safepoint yet)
+    _at_safepoint           =  1, // Thread at a safepoint (f.ex., when blocked on a lock)
+    _call_back              =  2  // Keep executing and wait for callback (if thread is in interpreted or vm)
+  };
+ private:
+  volatile bool _at_poll_safepoint;  // At polling page safepoint (NOT a poll return safepoint)
+  // Thread has called back the safepoint code (for debugging)
+  bool                           _has_called_back;
+
+  JavaThread *                   _thread;
+  volatile suspend_type          _type;
+
+
+ public:
+  ThreadSafepointState(JavaThread *thread);
+
+  // examine/roll-forward/restart
+  void examine_state_of_thread();
+  void roll_forward(suspend_type type);
+  void restart();
+
+  // Query
+  JavaThread*  thread() const         { return _thread; }
+  suspend_type type() const           { return _type; }
+  bool         is_running() const     { return (_type==_running); }
+
+  // Support for safepoint timeout (debugging)
+  bool has_called_back() const                   { return _has_called_back; }
+  void set_has_called_back(bool val)             { _has_called_back = val; }
+  bool              is_at_poll_safepoint() { return _at_poll_safepoint; }
+  void              set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
+
+  void handle_polling_page_exception();
+
+  // debugging
+  void print_on(outputStream* st) const;
+  void print() const                        { print_on(tty); }
+
+  // Initialize
+  static void create(JavaThread *thread);
+  static void destroy(JavaThread *thread);
+
+  void safepoint_msg(const char* format, ...) {
+    if (ShowSafepointMsgs) {
+      va_list ap;
+      va_start(ap, format);
+      tty->vprint_cr(format, ap);
+      va_end(ap);
+    }
+  }
+};
+
+//
+// CounterDecay
+//
+// Interates through invocation counters and decrements them. This
+// is done at each safepoint.
+//
+class CounterDecay : public AllStatic {
+  static jlong _last_timestamp;
+ public:
+  static  void decay();
+  static  bool is_decay_needed() { return (os::javaTimeMillis() - _last_timestamp) > CounterDecayMinIntervalLength; }
+};