1 /*

     2  * Copyright (c) 1997, 2015, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  *

    23  */

    24 

    25 #ifndef SHARE_VM_RUNTIME_TASK_HPP

    26 #define SHARE_VM_RUNTIME_TASK_HPP

    27 

    28 #include "memory/allocation.hpp"

    29 #include "runtime/timer.hpp"

    30 

    31 // A PeriodicTask has the sole purpose of executing its task

    32 // function with regular intervals.

    33 // Usage:

    34 //   PeriodicTask pf(10);

    35 //   pf.enroll();

    36 //   ...

    37 //   pf.disenroll();

    38 

    39 class PeriodicTask: public CHeapObj<mtInternal> {

    40  public:

    41   // Useful constants.

    42   // The interval constants are used to ensure the declared interval

    43   // is appropriate;  it must be between min_interval and max_interval,

    44   // and have a granularity of interval_gran (all in millis).

    45   enum { max_tasks     = 10,       // Max number of periodic tasks in system

    46          interval_gran = 10,

    47          min_interval  = 10,

    48          max_interval  = 10000 };

    49 

    50   static int num_tasks()   { return _num_tasks; }

    51 

    52  private:

    53   int _counter;

    54   const int _interval;

    55 

    56   static int _num_tasks;

    57   static PeriodicTask* _tasks[PeriodicTask::max_tasks];

    58   // Can only be called by the WatcherThread

    59   static void real_time_tick(int delay_time);

    60 

    61 #ifndef PRODUCT

    62   static elapsedTimer _timer;                      // measures time between ticks

    63   static int _ticks;                               // total number of ticks

    64   static int _intervalHistogram[max_interval];     // to check spacing of timer interrupts

    65  public:

    66   static void print_intervals();

    67 #endif

    68   // Only the WatcherThread can cause us to execute PeriodicTasks

    69   friend class WatcherThread;

    70  public:

    71   PeriodicTask(size_t interval_time); // interval is in milliseconds of elapsed time

    72   ~PeriodicTask();

    73 

    74   // Make the task active

    75   // For dynamic enrollment at the time T, the task will execute somewhere

    76   // between T and T + interval_time.

    77   void enroll();

    78 

    79   // Make the task deactive

    80   void disenroll();

    81 

    82   void execute_if_pending(int delay_time) {

    83     // make sure we don't overflow

    84     jlong tmp = (jlong) _counter + (jlong) delay_time;

    85 

    86     if (tmp >= (jlong) _interval) {

    87       _counter = 0;

    88       task();

    89     } else {

    90       _counter += delay_time;

    91     }

    92   }

    93 

    94   // Returns how long (time in milliseconds) before the next time we should

    95   // execute this task.

    96   int time_to_next_interval() const {

    97     assert(_interval > _counter,  "task counter greater than interval?");

    98     return _interval - _counter;

    99   }

   100 

   101   // Calculate when the next periodic task will fire.

   102   // Called by the WatcherThread's run method.

   103   // Requires the PeriodicTask_lock.

   104   static int time_to_wait();

   105 

   106   // The task to perform at each period

   107   virtual void task() = 0;

   108 };

   109 

   110 #endif // SHARE_VM_RUNTIME_TASK_HPP