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 /*

  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.

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

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  * 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

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  */

 #include "precompiled.hpp"

 #ifndef SERIALGC

 #include "utilities/yieldingWorkgroup.hpp"

 #endif

 // Forward declaration of classes declared here.

 class GangWorker;

 class WorkData;

 YieldingFlexibleWorkGang::YieldingFlexibleWorkGang(

   const char* name, uint workers, bool are_GC_task_threads) :

   FlexibleWorkGang(name, workers, are_GC_task_threads, false),

     _yielded_workers(0) {}

 GangWorker* YieldingFlexibleWorkGang::allocate_worker(uint which) {

   YieldingFlexibleGangWorker* new_member =

       new YieldingFlexibleGangWorker(this, which);

   return (YieldingFlexibleGangWorker*) new_member;

 }

 // Run a task; returns when the task is done, or the workers yield,

 // or the task is aborted, or the work gang is terminated via stop().

 // A task that has been yielded can be continued via this interface

 // by using the same task repeatedly as the argument to the call.

 // It is expected that the YieldingFlexibleGangTask carries the appropriate

 // continuation information used by workers to continue the task

 // from its last yield point. Thus, a completed task will return

 // immediately with no actual work having been done by the workers.

 /////////////////////

 // Implementatiuon notes: remove before checking XXX

 /*

 Each gang is working on a task at a certain time.

 Some subset of workers may have yielded and some may

 have finished their quota of work. Until this task has

 been completed, the workers are bound to that task.

 Once the task has been completed, the gang unbounds

 itself from the task.

 The yielding work gang thus exports two invokation

 interfaces: run_task() and continue_task(). The

 first is used to initiate a new task and bind it

 to the workers; the second is used to continue an

 already bound task that has yielded. Upon completion

 the binding is released and a new binding may be

 created.

 The shape of a yielding work gang is as follows:

 Overseer invokes run_task(*task).

    Lock gang monitor

    Check that there is no existing binding for the gang

    If so, abort with an error

    Else, create a new binding of this gang to the given task

    Set number of active workers (as asked)

    Notify workers that work is ready to be done

      [the requisite # workers would then start up

       and do the task]

    Wait on the monitor until either

      all work is completed or the task has yielded

      -- this is normally done through

         yielded + completed == active

         [completed workers are rest to idle state by overseer?]

    return appropriate status to caller

 Overseer invokes continue_task(*task),

    Lock gang monitor

    Check that task is the same as current binding

    If not, abort with an error

    Else, set the number of active workers as requested?

    Notify workers that they can continue from yield points

     New workers can also start up as required

       while satisfying the constraint that

          active + yielded does not exceed required number

    Wait (as above).

 NOTE: In the above, for simplicity in a first iteration

   our gangs will be of fixed population and will not

   therefore be flexible work gangs, just yielding work

   gangs. Once this works well, we will in a second

   iteration.refinement introduce flexibility into

   the work gang.

 NOTE: we can always create a new gang per each iteration

   in order to get the flexibility, but we will for now

   desist that simplified route.

  */

 /////////////////////

 void YieldingFlexibleWorkGang::start_task(YieldingFlexibleGangTask* new_task) {

   MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);

   assert(task() == NULL, "Gang currently tied to a task");

   assert(new_task != NULL, "Null task");

   // Bind task to gang

   _task = new_task;

   new_task->set_gang(this);  // Establish 2-way binding to support yielding

   _sequence_number++;

   uint requested_size = new_task->requested_size();

   assert(requested_size >= 0, "Should be non-negative");

   if (requested_size != 0) {

     _active_workers = MIN2(requested_size, total_workers());

   } else {

     _active_workers = active_workers();

   }

   new_task->set_actual_size(_active_workers);

   new_task->set_for_termination(_active_workers);

   assert(_started_workers == 0, "Tabula rasa non");

   assert(_finished_workers == 0, "Tabula rasa non");

   assert(_yielded_workers == 0, "Tabula rasa non");

   yielding_task()->set_status(ACTIVE);

   // Wake up all the workers, the first few will get to work,

   // and the rest will go back to sleep

   monitor()->notify_all();

   wait_for_gang();

 }

 void YieldingFlexibleWorkGang::wait_for_gang() {

   assert(monitor()->owned_by_self(), "Data race");

   // Wait for task to complete or yield

   for (Status status = yielding_task()->status();

        status != COMPLETED && status != YIELDED && status != ABORTED;

        status = yielding_task()->status()) {

     assert(started_workers() <= active_workers(), "invariant");

     assert(finished_workers() <= active_workers(), "invariant");

     assert(yielded_workers() <= active_workers(), "invariant");

     monitor()->wait(Mutex::_no_safepoint_check_flag);

   }

   switch (yielding_task()->status()) {

     case COMPLETED:

     case ABORTED: {

       assert(finished_workers() == active_workers(), "Inconsistent status");

       assert(yielded_workers() == 0, "Invariant");

       reset();   // for next task; gang<->task binding released

       break;

     }

     case YIELDED: {

       assert(yielded_workers() > 0, "Invariant");

       assert(yielded_workers() + finished_workers() == active_workers(),

              "Inconsistent counts");

       break;

     }

     case ACTIVE:

     case INACTIVE:

     case COMPLETING:

     case YIELDING:

     case ABORTING:

     default:

       ShouldNotReachHere();

   }

 }

 void YieldingFlexibleWorkGang::continue_task(

   YieldingFlexibleGangTask* gang_task) {

   MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);

   assert(task() != NULL && task() == gang_task, "Incorrect usage");

   assert(_started_workers == _active_workers, "Precondition");

   assert(_yielded_workers > 0 && yielding_task()->status() == YIELDED,

          "Else why are we calling continue_task()");

   // Restart the yielded gang workers

   yielding_task()->set_status(ACTIVE);

   monitor()->notify_all();

   wait_for_gang();

 }

 void YieldingFlexibleWorkGang::reset() {

   _started_workers  = 0;

   _finished_workers = 0;

   yielding_task()->set_gang(NULL);

   _task = NULL;    // unbind gang from task

 }

 void YieldingFlexibleWorkGang::yield() {

   assert(task() != NULL, "Inconsistency; should have task binding");

   MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);

   assert(yielded_workers() < active_workers(), "Consistency check");

   if (yielding_task()->status() == ABORTING) {

     // Do not yield; we need to abort as soon as possible

     // XXX NOTE: This can cause a performance pathology in the

     // current implementation in Mustang, as of today, and

     // pre-Mustang in that as soon as an overflow occurs,

     // yields will not be honoured. The right way to proceed

     // of course is to fix bug # TBF, so that abort's cause

     // us to return at each potential yield point.

     return;

   }

   if (++_yielded_workers + finished_workers() == active_workers()) {

     yielding_task()->set_status(YIELDED);

     monitor()->notify_all();

   } else {

     yielding_task()->set_status(YIELDING);

   }

   while (true) {

     switch (yielding_task()->status()) {

       case YIELDING:

       case YIELDED: {

         monitor()->wait(Mutex::_no_safepoint_check_flag);

         break;  // from switch

       }

       case ACTIVE:

       case ABORTING:

       case COMPLETING: {

         assert(_yielded_workers > 0, "Else why am i here?");

         _yielded_workers--;

         return;

       }

       case INACTIVE:

       case ABORTED:

       case COMPLETED:

       default: {

         ShouldNotReachHere();

       }

     }

   }

   // Only return is from inside switch statement above

   ShouldNotReachHere();

 }

 void YieldingFlexibleWorkGang::abort() {

   assert(task() != NULL, "Inconsistency; should have task binding");

   MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);

   assert(yielded_workers() < active_workers(), "Consistency check");

   #ifndef PRODUCT

     switch (yielding_task()->status()) {

       // allowed states

       case ACTIVE:

       case ABORTING:

       case COMPLETING:

       case YIELDING:

         break;

       // not allowed states

       case INACTIVE:

       case ABORTED:

       case COMPLETED:

       case YIELDED:

       default:

         ShouldNotReachHere();

     }

   #endif // !PRODUCT

   Status prev_status = yielding_task()->status();

   yielding_task()->set_status(ABORTING);

   if (prev_status == YIELDING) {

     assert(yielded_workers() > 0, "Inconsistency");

     // At least one thread has yielded, wake it up

     // so it can go back to waiting stations ASAP.

     monitor()->notify_all();

   }

 }

 ///////////////////////////////

 // YieldingFlexibleGangTask

 ///////////////////////////////

 void YieldingFlexibleGangTask::yield() {

   assert(gang() != NULL, "No gang to signal");

   gang()->yield();

 }

 void YieldingFlexibleGangTask::abort() {

   assert(gang() != NULL, "No gang to signal");

   gang()->abort();

 }

 ///////////////////////////////

 // YieldingFlexibleGangWorker

 ///////////////////////////////

 void YieldingFlexibleGangWorker::loop() {

   int previous_sequence_number = 0;

   Monitor* gang_monitor = gang()->monitor();

   MutexLockerEx ml(gang_monitor, Mutex::_no_safepoint_check_flag);

   WorkData data;

   int id;

   while (true) {

     // Check if there is work to do or if we have been asked

     // to terminate

     gang()->internal_worker_poll(&data);

     if (data.terminate()) {

       // We have been asked to terminate.

       assert(gang()->task() == NULL, "No task binding");

       // set_status(TERMINATED);

       return;

     } else if (data.task() != NULL &&

                data.sequence_number() != previous_sequence_number) {

       // There is work to be done.

       // First check if we need to become active or if there

       // are already the requisite number of workers

       if (gang()->started_workers() == yf_gang()->active_workers()) {

         // There are already enough workers, we do not need to

         // to run; fall through and wait on monitor.

       } else {

         // We need to pitch in and do the work.

         assert(gang()->started_workers() < yf_gang()->active_workers(),

                "Unexpected state");

         id = gang()->started_workers();

         gang()->internal_note_start();

         // Now, release the gang mutex and do the work.

         {

           MutexUnlockerEx mul(gang_monitor, Mutex::_no_safepoint_check_flag);

           data.task()->work(id);   // This might include yielding

         }

         // Reacquire monitor and note completion of this worker

         gang()->internal_note_finish();

         // Update status of task based on whether all workers have

         // finished or some have yielded

         assert(data.task() == gang()->task(), "Confused task binding");

         if (gang()->finished_workers() == yf_gang()->active_workers()) {

           switch (data.yf_task()->status()) {

             case ABORTING: {

               data.yf_task()->set_status(ABORTED);

               break;

             }

             case ACTIVE:

             case COMPLETING: {

               data.yf_task()->set_status(COMPLETED);

               break;

             }

             default:

               ShouldNotReachHere();

           }

           gang_monitor->notify_all();  // Notify overseer

         } else { // at least one worker is still working or yielded

           assert(gang()->finished_workers() < yf_gang()->active_workers(),

                  "Counts inconsistent");

           switch (data.yf_task()->status()) {

             case ACTIVE: {

               // first, but not only thread to complete

               data.yf_task()->set_status(COMPLETING);

               break;

             }

             case YIELDING: {

               if (gang()->finished_workers() + yf_gang()->yielded_workers()

                   == yf_gang()->active_workers()) {

                 data.yf_task()->set_status(YIELDED);

                 gang_monitor->notify_all();  // notify overseer

               }

               break;

             }

             case ABORTING:

             case COMPLETING: {

               break; // nothing to do

             }

             default: // everything else: INACTIVE, YIELDED, ABORTED, COMPLETED

               ShouldNotReachHere();

           }

         }

       }

     }

     // Remember the sequence number

     previous_sequence_number = data.sequence_number();

     // Wait for more work

     gang_monitor->wait(Mutex::_no_safepoint_check_flag);

   }

 }