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 /*
     Copyright (c) 2005-2020 Intel Corporation
 
     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
     You may obtain a copy of the License at
 
         http://www.apache.org/licenses/LICENSE-2.0
 
     Unless required by applicable law or agreed to in writing, software
     distributed under the License is distributed on an "AS IS" BASIS,
     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     See the License for the specific language governing permissions and
     limitations under the License.
 */
 
 #ifndef __TBB_task_scheduler_observer_H
 #define __TBB_task_scheduler_observer_H
 
 #define __TBB_task_scheduler_observer_H_include_area
 #include "internal/_warning_suppress_enable_notice.h"
 
 #include "atomic.h"
 #if __TBB_ARENA_OBSERVER
 #include "task_arena.h"
 #endif
 
 #if __TBB_SCHEDULER_OBSERVER
 
 namespace tbb {
 namespace interface6 {
 class task_scheduler_observer;
 }
 namespace internal {
 
 class observer_proxy;
 class observer_list;
 
 class task_scheduler_observer_v3 {
     friend class observer_proxy;
     friend class observer_list;
     friend class interface6::task_scheduler_observer;
 
     //! Pointer to the proxy holding this observer.
     /** Observers are proxied by the scheduler to maintain persistent lists of them. **/
     observer_proxy* my_proxy;
 
     //! Counter preventing the observer from being destroyed while in use by the scheduler.
     /** Valid only when observation is on. **/
     atomic<intptr_t> my_busy_count;
 
 public:
     //! Enable or disable observation
     /** For local observers the method can be used only when the current thread
         has the task scheduler initialized or is attached to an arena.
 
         Repeated calls with the same state are no-ops. **/
     void __TBB_EXPORTED_METHOD observe( bool state=true );
 
     //! Returns true if observation is enabled, false otherwise.
     bool is_observing() const {return my_proxy!=NULL;}
 
     //! Construct observer with observation disabled.
     task_scheduler_observer_v3() : my_proxy(NULL) { my_busy_count.store<relaxed>(0); }
 
     //! Entry notification
     /** Invoked from inside observe(true) call and whenever a worker enters the arena
         this observer is associated with. If a thread is already in the arena when
         the observer is activated, the entry notification is called before it
         executes the first stolen task.
 
         Obsolete semantics. For global observers it is called by a thread before
         the first steal since observation became enabled. **/
     virtual void on_scheduler_entry( bool /*is_worker*/ ) {}
 
     //! Exit notification
     /** Invoked from inside observe(false) call and whenever a worker leaves the
         arena this observer is associated with.
 
         Obsolete semantics. For global observers it is called by a thread before
         the first steal since observation became enabled. **/
     virtual void on_scheduler_exit( bool /*is_worker*/ ) {}
 
     //! Destructor automatically switches observation off if it is enabled.
     virtual ~task_scheduler_observer_v3() { if(my_proxy) observe(false);}
 };
 
 } // namespace internal
 
 #if __TBB_ARENA_OBSERVER
 namespace interface6 {
 class task_scheduler_observer : public internal::task_scheduler_observer_v3 {
     friend class internal::task_scheduler_observer_v3;
     friend class internal::observer_proxy;
     friend class internal::observer_list;
 
     /** Negative numbers with the largest absolute value to minimize probability
         of coincidence in case of a bug in busy count usage. **/
     // TODO: take more high bits for version number
     static const intptr_t v6_trait = (intptr_t)((~(uintptr_t)0 >> 1) + 1);
 
     //! contains task_arena pointer or tag indicating local or global semantics of the observer
     intptr_t my_context_tag;
     enum { global_tag = 0, implicit_tag = 1 };
 
 public:
     //! Construct local or global observer in inactive state (observation disabled).
     /** For a local observer entry/exit notifications are invoked whenever a worker
         thread joins/leaves the arena of the observer's owner thread. If a thread is
         already in the arena when the observer is activated, the entry notification is
         called before it executes the first stolen task. **/
     /** TODO: Obsolete.
         Global observer semantics is obsolete as it violates master thread isolation
         guarantees and is not composable. Thus the current default behavior of the
         constructor is obsolete too and will be changed in one of the future versions
         of the library. **/
     explicit task_scheduler_observer( bool local = false ) {
 #if  __TBB_ARENA_OBSERVER
         my_context_tag = local? implicit_tag : global_tag;
 #else
         __TBB_ASSERT_EX( !local, NULL );
         my_context_tag = global_tag;
 #endif
     }
 
 #if  __TBB_ARENA_OBSERVER
     //! Construct local observer for a given arena in inactive state (observation disabled).
     /** entry/exit notifications are invoked whenever a thread joins/leaves arena.
         If a thread is already in the arena when the observer is activated, the entry notification
         is called before it executes the first stolen task. **/
     explicit task_scheduler_observer( task_arena & a) {
         my_context_tag = (intptr_t)&a;
     }
 #endif /* __TBB_ARENA_OBSERVER */
 
     /** Destructor protects instance of the observer from concurrent notification.
        It is recommended to disable observation before destructor of a derived class starts,
        otherwise it can lead to concurrent notification callback on partly destroyed object **/
     virtual ~task_scheduler_observer() { if(my_proxy) observe(false); }
 
     //! Enable or disable observation
     /** Warning: concurrent invocations of this method are not safe.
         Repeated calls with the same state are no-ops. **/
     void observe( bool state=true ) {
         if( state && !my_proxy ) {
             __TBB_ASSERT( !my_busy_count, "Inconsistent state of task_scheduler_observer instance");
             my_busy_count.store<relaxed>(v6_trait);
         }
         internal::task_scheduler_observer_v3::observe(state);
     }
 };
 
 } //namespace interface6
 using interface6::task_scheduler_observer;
 #else /*__TBB_ARENA_OBSERVER*/
 typedef tbb::internal::task_scheduler_observer_v3 task_scheduler_observer;
 #endif /*__TBB_ARENA_OBSERVER*/
 
 } // namespace tbb
 
 #endif /* __TBB_SCHEDULER_OBSERVER */
 
 #include "internal/_warning_suppress_disable_notice.h"
 #undef __TBB_task_scheduler_observer_H_include_area
 
 #endif /* __TBB_task_scheduler_observer_H */

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