/*
    Copyright 2005-2013 Intel Corporation.  All Rights Reserved.

    This file is part of Threading Building Blocks.

    Threading Building Blocks is free software; you can redistribute it
    and/or modify it under the terms of the GNU General Public License
    version 2 as published by the Free Software Foundation.

    Threading Building Blocks 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 for more details.

    You should have received a copy of the GNU General Public License
    along with Threading Building Blocks; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    As a special exception, you may use this file as part of a free software
    library without restriction.  Specifically, if other files instantiate
    templates or use macros or inline functions from this file, or you compile
    this file and link it with other files to produce an executable, this
    file does not by itself cause the resulting executable to be covered by
    the GNU General Public License.  This exception does not however
    invalidate any other reasons why the executable file might be covered by
    the GNU General Public License.
*/

#ifndef _TBB_scheduler_H
#define _TBB_scheduler_H

#include "scheduler_common.h"
#include "tbb/spin_mutex.h"
#include "mailbox.h"
#include "tbb_misc.h" // for FastRandom
#include "itt_notify.h"
#include "../rml/include/rml_tbb.h"

#if __TBB_SURVIVE_THREAD_SWITCH
#include "cilk-tbb-interop.h"
#endif /* __TBB_SURVIVE_THREAD_SWITCH */

namespace tbb {
namespace internal {

template<typename SchedulerTraits> class custom_scheduler;

//------------------------------------------------------------------------
// generic_scheduler
//------------------------------------------------------------------------

#if __TBB_TASK_GROUP_CONTEXT
struct scheduler_list_node_t {
    scheduler_list_node_t *my_prev,
                          *my_next;
};
#endif /* __TBB_TASK_GROUP_CONTEXT */

#define EmptyTaskPool ((task**)0)
#define LockedTaskPool ((task**)~(intptr_t)0)

#define LockedMaster ((generic_scheduler*)~(intptr_t)0)

class governor;
class market;
class arena;

#if __TBB_SCHEDULER_OBSERVER
class task_scheduler_observer_v3;
class observer_proxy;
#endif /* __TBB_SCHEDULER_OBSERVER */

struct scheduler_state {
    //! Index of the arena slot the scheduler occupies now, or occupied last time.
    size_t my_arena_index;

    //! Pointer to the slot in the arena we own at the moment.
    arena_slot* my_arena_slot;

    //! The arena that I own (if master) or am servicing at the moment (if worker)
    arena* my_arena;

    //! Innermost task whose task::execute() is running.
    task* my_innermost_running_task;

    //! Task, in the context of which the current TBB dispatch loop is running.
    /** Outside of or in the outermost dispatch loop (not in a nested call to
        wait_for_all) it is my_dummy_task for master threads, and NULL for workers. **/
    task* my_dispatching_task;

    mail_inbox my_inbox;

    //! The mailbox id assigned to this scheduler.
    /** The id is assigned upon first entry into the arena.
        TODO: how are id's being garbage collected?
        TODO: master thread may enter arena and leave and then reenter.
                We want to give it the same affinity_id upon reentry, if practical.
      */
    affinity_id my_affinity_id;

#if __TBB_SCHEDULER_OBSERVER
    //! Last observer in the global observers list processed by this scheduler
    observer_proxy* my_last_global_observer;

    //! Last observer in the local observers list processed by this scheduler
    observer_proxy* my_last_local_observer;
#endif /* __TBB_SCHEDULER_OBSERVER */
};

//! Work stealing task scheduler.
/** None of the fields here are ever read or written by threads other than
    the thread that creates the instance.

    Class generic_scheduler is an abstract base class that contains most of the scheduler,
    except for tweaks specific to processors and tools (e.g. VTune).
    The derived template class custom_scheduler<SchedulerTraits> fills in the tweaks. */
class generic_scheduler: public scheduler, public ::rml::job, private scheduler_state {
    friend class tbb::task;
    friend class market;
    friend class arena;
#if __TBB_TASK_ARENA
    friend class interface6::task_arena;
    friend class interface6::wait_task;
    friend struct interface6::wait_body;
#endif //__TBB_TASK_ARENA
    friend class allocate_root_proxy;
    friend class governor;
#if __TBB_TASK_GROUP_CONTEXT
    friend class allocate_root_with_context_proxy;
    friend class tbb::task_group_context;
#endif /* __TBB_TASK_GROUP_CONTEXT */
#if __TBB_SCHEDULER_OBSERVER
    friend class task_scheduler_observer_v3;
#endif /* __TBB_SCHEDULER_OBSERVER */
    friend class scheduler;
    template<typename SchedulerTraits> friend class custom_scheduler;

    //! If sizeof(task) is <=quick_task_size, it is handled on a free list instead of malloc'd.
    static const size_t quick_task_size = 256-task_prefix_reservation_size;

    static bool is_version_3_task( task& t ) {
        return (t.prefix().extra_state & 0x0F)>=0x1;
    }

    //! Position in the call stack specifying its maximal filling when stealing is still allowed
    uintptr_t my_stealing_threshold;
#if __TBB_ipf
    //! Position in the RSE backup area specifying its maximal filling when stealing is still allowed
    uintptr_t my_rsb_stealing_threshold;
#endif

    static const size_t null_arena_index = ~size_t(0);

    // TODO: Rename into is_task_pool_published()
    inline bool in_arena () const;

    inline bool is_local_task_pool_quiescent () const;

    inline bool is_quiescent_local_task_pool_empty () const;

    inline bool is_quiescent_local_task_pool_reset () const;

    //! The market I am in
    market* my_market;

    //! Random number generator used for picking a random victim from which to steal.
    FastRandom my_random;

    //! Hint provided for operations with the container of starvation-resistant tasks.
    /** Modified by the owner thread (during these operations). **/
    unsigned hint_for_push; //TODO: Replace by my_random?

    //! Free list of small tasks that can be reused.
    task* my_free_list;

#if __TBB_HOARD_NONLOCAL_TASKS
    //! Free list of small non-local tasks that should be returned or can be reused.
    task* my_nonlocal_free_list;
#endif
    //! Fake root task created by slave threads.
    /** The task is used as the "parent" argument to method wait_for_all. */
    task* my_dummy_task;

    //! Reference count for scheduler
    /** Number of task_scheduler_init objects that point to this scheduler */
    long my_ref_count;

    inline void attach_mailbox( affinity_id id );

    /* A couple of bools can be located here because space is otherwise just padding after my_affinity_id. */

    //! True if *this was created by automatic TBB initialization
    bool my_auto_initialized;

#if __TBB_COUNT_TASK_NODES
    //! Net number of big task objects that have been allocated but not yet freed.
    intptr_t my_task_node_count;
#endif /* __TBB_COUNT_TASK_NODES */

    //! Sets up the data necessary for the stealing limiting heuristics
    void init_stack_info ();

    //! Returns true if stealing is allowed
    bool can_steal () {
        int anchor;
        // TODO IDEA: Add performance warning?
#if __TBB_ipf
        return my_stealing_threshold < (uintptr_t)&anchor && (uintptr_t)__TBB_get_bsp() < my_rsb_stealing_threshold;
#else
        return my_stealing_threshold < (uintptr_t)&anchor;
#endif
    }

    //! Actions common to enter_arena and try_enter_arena
    void do_enter_arena();

    //! Used by workers to enter the arena 
    /** Does not lock the task pool in case if arena slot has been successfully grabbed. **/
    void enter_arena();

    //! Leave the arena
    /** Leaving arena automatically releases the task pool if it is locked. **/
    void leave_arena();

    //! Resets head and tail indices to 0, and leaves arena
    /** Argument specifies whether the task pool is currently locked by the owner
        (via acquire_task_pool).**/
    inline void reset_deque_and_leave_arena ( bool locked );

    //! Locks victim's task pool, and returns pointer to it. The pointer can be NULL.
    /** Garbles victim_arena_slot->task_pool for the duration of the lock. **/
    task** lock_task_pool( arena_slot* victim_arena_slot ) const;

    //! Unlocks victim's task pool
    /** Restores victim_arena_slot->task_pool munged by lock_task_pool. **/
    void unlock_task_pool( arena_slot* victim_arena_slot, task** victim_task_pool ) const;

    //! Locks the local task pool
    /** Garbles my_arena_slot->task_pool for the duration of the lock. Requires
        correctly set my_arena_slot->task_pool_ptr. **/
    void acquire_task_pool() const;

    //! Unlocks the local task pool
    /** Restores my_arena_slot->task_pool munged by acquire_task_pool. Requires
        correctly set my_arena_slot->task_pool_ptr. **/
    void release_task_pool() const;

    //! Checks if t is affinitized to another thread, and if so, bundles it as proxy.
    /** Returns either t or proxy containing t. **/
    task* prepare_for_spawning( task* t );

    //! Makes newly spawned tasks visible to thieves
    inline void commit_spawned_tasks( size_t new_tail );

    //! Makes relocated tasks visible to thieves and releases the local task pool.
    /** Obviously, the task pool must be locked when calling this method. **/
    inline void commit_relocated_tasks( size_t new_tail );

    //! Get a task from the local pool.
    /** Called only by the pool owner.
        Returns the pointer to the task or NULL if the pool is empty. 
        In the latter case compacts the pool. **/
    task* get_task();

    //! Attempt to get a task from the mailbox.
    /** Gets a task only if it has not been executed by its sender or a thief 
        that has stolen it from the sender's task pool. Otherwise returns NULL.

        This method is intended to be used only by the thread extracting the proxy 
        from its mailbox. (In contrast to local task pool, mailbox can be read only
        by its owner). **/
    task* get_mailbox_task();

    //! True if t is a task_proxy
    static bool is_proxy( const task& t ) {
        return t.prefix().extra_state==es_task_proxy;
    }

    //! Get a task from the starvation-resistant task stream of the current arena.
    /** Returns the pointer to the task, or NULL if the attempt was unsuccessful. 
        The latter case does not mean that the stream is drained, however. **/
    task* dequeue_task();

    //! Steal task from another scheduler's ready pool.
    task* steal_task( arena_slot& victim_arena_slot );

    /** Initial size of the task deque sufficient to serve without reallocation
        4 nested parallel_for calls with iteration space of 65535 grains each. **/
    static const size_t min_task_pool_size = 64;

    //! Makes sure that the task pool can accommodate at least n more elements
    /** If necessary relocates existing task pointers or grows the ready task deque.
        Returns (possible updated) tail index (not accounting for n). **/
    size_t prepare_task_pool( size_t n );

    //! Initialize a scheduler for a master thread.
    static generic_scheduler* create_master( arena& a );

    //! Perform necessary cleanup when a master thread stops using TBB.
    void cleanup_master();

    //! Initialize a scheduler for a worker thread.
    static generic_scheduler* create_worker( market& m, size_t index );

    //! Perform necessary cleanup when a worker thread finishes.
    static void cleanup_worker( void* arg, bool worker );

protected:
    generic_scheduler( arena*, size_t index );

#if TBB_USE_ASSERT > 1
    //! Check that internal data structures are in consistent state.
    /** Raises __TBB_ASSERT failure if inconsistency is found. */
    void assert_task_pool_valid () const;
#else
    void assert_task_pool_valid() const {}
#endif /* TBB_USE_ASSERT <= 1 */

public:
#if __TBB_TASK_ARENA
    template<typename Body>
    void nested_arena_execute(arena*, task*, bool, Body&);
#endif

    /*override*/ 
    void spawn( task& first, task*& next );

    /*override*/ 
    void spawn_root_and_wait( task& first, task*& next );

    /*override*/ 
    void enqueue( task&, void* reserved );

    void local_spawn( task& first, task*& next );
    void local_spawn_root_and_wait( task& first, task*& next );
    virtual void local_wait_for_all( task& parent, task* child ) = 0;

    //! Destroy and deallocate this scheduler object
    void free_scheduler();

    //! Allocate task object, either from the heap or a free list.
    /** Returns uninitialized task object with initialized prefix. */
    task& allocate_task( size_t number_of_bytes, 
                       __TBB_CONTEXT_ARG(task* parent, task_group_context* context) );

    //! Put task on free list.
    /** Does not call destructor. */
    template<free_task_hint h>
    void free_task( task& t );

    //! Return task object to the memory allocator.
    inline void deallocate_task( task& t );

    //! True if running on a worker thread, false otherwise.
    inline bool is_worker();

    //! True if the scheduler is on the outermost dispatch level in a master thread.
    /** Returns true when this scheduler instance is associated with an application
        thread, and is not executing any TBB task. This includes being in a TBB 
        dispatch loop (one of wait_for_all methods) invoked directly from that thread. **/
    inline bool master_outermost_level () const;

#if __TBB_TASK_GROUP_CONTEXT
    //! Returns task group context used by this scheduler instance.
    /** This context is associated with root tasks created by a master thread 
        without explicitly specified context object outside of any running task.
        
        Note that the default context of a worker thread is never accessed by
        user code (directly or indirectly). **/
    inline task_group_context* default_context ();
#endif /* __TBB_TASK_GROUP_CONTEXT */

    //! Returns number of worker threads in the arena this thread belongs to.
    unsigned number_of_workers_in_my_arena();

#if __TBB_COUNT_TASK_NODES
    intptr_t get_task_node_count( bool count_arena_workers = false );
#endif /* __TBB_COUNT_TASK_NODES */

    //! Special value used to mark my_return_list as not taking any more entries.
    static task* plugged_return_list() {return (task*)(intptr_t)(-1);}

    //! Number of small tasks that have been allocated by this scheduler. 
    intptr_t my_small_task_count;

    //! List of small tasks that have been returned to this scheduler by other schedulers.
    task* my_return_list;

    //! Try getting a task from other threads (via mailbox, stealing, FIFO queue, orphans adoption).
    /** Returns obtained task or NULL if all attempts fail. */
    virtual task* receive_or_steal_task( __TBB_atomic reference_count& completion_ref_count,
                                         bool return_if_no_work ) = 0;

    //! Free a small task t that that was allocated by a different scheduler 
    void free_nonlocal_small_task( task& t ); 

#if __TBB_TASK_GROUP_CONTEXT
    //! Padding isolating thread-local members from members that can be written to by other threads.
    char _padding1[NFS_MaxLineSize - sizeof(context_list_node_t)];

    //! Head of the thread specific list of task group contexts.
    context_list_node_t my_context_list_head;

    //! Mutex protecting access to the list of task group contexts.
    // TODO: check whether it can be deadly preempted and replace by spinning/sleeping mutex
    spin_mutex my_context_list_mutex;

    //! Last state propagation epoch known to this thread 
    /** Together with the_context_state_propagation_epoch constitute synchronization protocol
        that keeps hot path of task group context construction destruction mostly 
        lock-free.
        When local epoch equals the global one, the state of task group contexts
        registered with this thread is consistent with that of the task group trees
        they belong to. **/
    uintptr_t my_context_state_propagation_epoch;

    //! Flag indicating that a context is being destructed by its owner thread 
    /** Together with my_nonlocal_ctx_list_update constitute synchronization protocol
        that keeps hot path of context destruction (by the owner thread) mostly 
        lock-free. **/
    tbb::atomic<uintptr_t> my_local_ctx_list_update;

#if __TBB_TASK_PRIORITY
    //! True if the scheduler is on the outermost dispatch level in a worker thread.
    inline bool worker_outermost_level () const;

    //! Returns reference priority used to decide whether a task should be offloaded.
    inline intptr_t effective_reference_priority () const;

    //! Latest known highest priority of tasks in the market or arena.
    /** Master threads currently tracks only tasks in their arenas, while workers
        take into account global top priority (among all arenas in the market). **/
    volatile intptr_t *my_ref_top_priority;

    // TODO: move into slots and fix is_out_of_work
    //! Task pool for offloading tasks with priorities lower than the current top priority.
    task* my_offloaded_tasks;

    //! Points to the last offloaded task in the my_offloaded_tasks list.
    task** my_offloaded_task_list_tail_link;

    //! Pointer to market's (for workers) or current arena's (for the master) reload epoch counter.
    volatile uintptr_t *my_ref_reload_epoch;

    //! Indicator of how recently the offload area was checked for the presence of top priority tasks.
    uintptr_t my_local_reload_epoch;

    //! Indicates that the pool is likely non-empty even if appears so from outside
    volatile bool my_pool_reshuffling_pending;

    //! Searches offload area for top priority tasks and reloads found ones into primary task pool.
    /** Returns one of the found tasks or NULL. **/
    task* reload_tasks ();

    task* reload_tasks ( task*& offloaded_tasks, task**& offloaded_task_list_link, intptr_t top_priority );

    //! Moves tasks with priority below the top one from primary task pool into offload area.
    /** Returns the next execution candidate task or NULL. **/
    task* winnow_task_pool ();

    //! Unconditionally moves the task into offload area.
    inline void offload_task ( task& t, intptr_t task_priority );
#endif /* __TBB_TASK_PRIORITY */

    //! Detaches abandoned contexts
    /** These contexts must be destroyed by other threads. **/
    void cleanup_local_context_list ();

    //! Finds all contexts registered by this scheduler affected by the state change
    //! and propagates the new state to them.
    template <typename T>
    void propagate_task_group_state ( T task_group_context::*mptr_state, T new_state );
#endif /* __TBB_TASK_GROUP_CONTEXT */

#if _WIN32||_WIN64
private:
    //! Handle returned by RML when registering a master with RML
    ::rml::server::execution_resource_t master_exec_resource;
#endif /* _WIN32||_WIN64 */

#if __TBB_TASK_GROUP_CONTEXT
    //! Flag indicating that a context is being destructed by non-owner thread.
    /** See also my_local_ctx_list_update. **/
    tbb::atomic<uintptr_t> my_nonlocal_ctx_list_update;
#endif /* __TBB_TASK_GROUP_CONTEXT */

#if __TBB_SURVIVE_THREAD_SWITCH
    __cilk_tbb_unwatch_thunk my_cilk_unwatch_thunk;
#if TBB_USE_ASSERT
    //! State values used to check interface contract with cilkrts.
    /** Names of cs_running...cs_freed derived from state machine diagram in cilk-tbb-interop.h */
    enum cilk_state_t {
        cs_none=0xF000, // Start at nonzero value so that we can detect use of zeroed memory.
        cs_running,
        cs_limbo,
        cs_freed
    };
    cilk_state_t my_cilk_state;
#endif /* TBB_USE_ASSERT */
#endif /* __TBB_SURVIVE_THREAD_SWITCH */

#if __TBB_STATISTICS
    //! Set of counters to track internal statistics on per thread basis
    /** Placed at the end of the class definition to minimize the disturbance of
        the core logic memory operations. **/
    mutable statistics_counters my_counters;
#endif /* __TBB_STATISTICS */

}; // class generic_scheduler


} // namespace internal
} // namespace tbb

#include "arena.h"
#include "governor.h"

namespace tbb {
namespace internal {

inline bool generic_scheduler::in_arena () const {
    __TBB_ASSERT(my_arena_slot, 0);
    return my_arena_slot->task_pool != EmptyTaskPool;
}

inline bool generic_scheduler::is_local_task_pool_quiescent () const {
    __TBB_ASSERT(my_arena_slot, 0);
    task** tp = my_arena_slot->task_pool;
    return tp == EmptyTaskPool || tp == LockedTaskPool;
}

inline bool generic_scheduler::is_quiescent_local_task_pool_empty () const {
    __TBB_ASSERT( is_local_task_pool_quiescent(), "Task pool is not quiescent" );
    return __TBB_load_relaxed(my_arena_slot->head) == __TBB_load_relaxed(my_arena_slot->tail);
}

inline bool generic_scheduler::is_quiescent_local_task_pool_reset () const {
    __TBB_ASSERT( is_local_task_pool_quiescent(), "Task pool is not quiescent" );
    return __TBB_load_relaxed(my_arena_slot->head) == 0 && __TBB_load_relaxed(my_arena_slot->tail) == 0;
}

inline bool generic_scheduler::master_outermost_level () const {
    return my_dispatching_task == my_dummy_task;
}

#if __TBB_TASK_GROUP_CONTEXT
inline task_group_context* generic_scheduler::default_context () {
    return my_dummy_task->prefix().context;
}
#endif /* __TBB_TASK_GROUP_CONTEXT */

inline void generic_scheduler::attach_mailbox( affinity_id id ) {
    __TBB_ASSERT(id>0,NULL);
    my_inbox.attach( my_arena->mailbox(id) );
    my_affinity_id = id;
}

inline bool generic_scheduler::is_worker() {
    return my_arena_index != 0; //TODO: rework for multiple master
}

inline unsigned generic_scheduler::number_of_workers_in_my_arena() {
    return my_arena->my_max_num_workers;
}

//! Return task object to the memory allocator.
inline void generic_scheduler::deallocate_task( task& t ) {
#if TBB_USE_ASSERT
    task_prefix& p = t.prefix();
    p.state = 0xFF;
    p.extra_state = 0xFF; 
    poison_pointer(p.next);
#endif /* TBB_USE_ASSERT */
    NFS_Free((char*)&t-task_prefix_reservation_size);
#if __TBB_COUNT_TASK_NODES
    --my_task_node_count;
#endif /* __TBB_COUNT_TASK_NODES */
}

#if __TBB_COUNT_TASK_NODES
inline intptr_t generic_scheduler::get_task_node_count( bool count_arena_workers ) {
    return my_task_node_count + (count_arena_workers? my_arena->workers_task_node_count(): 0);
}
#endif /* __TBB_COUNT_TASK_NODES */

inline void generic_scheduler::reset_deque_and_leave_arena ( bool locked ) {
    if ( !locked )
        acquire_task_pool();
    __TBB_store_relaxed( my_arena_slot->tail, 0 );
    __TBB_store_relaxed( my_arena_slot->head, 0 );
    leave_arena();
}

//TODO: move to arena_slot
inline void generic_scheduler::commit_spawned_tasks( size_t new_tail ) {
    __TBB_ASSERT ( new_tail <= my_arena_slot->my_task_pool_size, "task deque end was overwritten" );
    // emit "task was released" signal
    ITT_NOTIFY(sync_releasing, (void*)((uintptr_t)my_arena_slot+sizeof(uintptr_t)));
    // Release fence is necessary to make sure that previously stored task pointers
    // are visible to thieves.
    __TBB_store_with_release( my_arena_slot->tail, new_tail );
}

void generic_scheduler::commit_relocated_tasks ( size_t new_tail ) {
    __TBB_ASSERT( is_local_task_pool_quiescent(),
                  "Task pool must be locked when calling commit_relocated_tasks()" );
    __TBB_store_relaxed( my_arena_slot->head, 0 );
    // Tail is updated last to minimize probability of a thread making arena 
    // snapshot being misguided into thinking that this task pool is empty.
    __TBB_store_relaxed( my_arena_slot->tail, new_tail );
    release_task_pool();
}

template<free_task_hint hint>
void generic_scheduler::free_task( task& t ) {
#if __TBB_HOARD_NONLOCAL_TASKS
    // TODO: remove the whole free_task_hint stuff when enabled permanently
    static const free_task_hint h = no_hint;
#else
    static const free_task_hint h = hint;
#endif
    GATHER_STATISTIC(--my_counters.active_tasks);
    task_prefix& p = t.prefix();
    // Verify that optimization hints are correct.
    __TBB_ASSERT( h!=small_local_task || p.origin==this, NULL );
    __TBB_ASSERT( !(h&small_task) || p.origin, NULL );
    poison_value(p.depth);
    poison_value(p.ref_count);
    poison_pointer(p.owner);
    __TBB_ASSERT( 1L<<t.state() & (1L<<task::executing|1L<<task::allocated), NULL );
    p.state = task::freed;
    if( h==small_local_task || p.origin==this ) {
        GATHER_STATISTIC(++my_counters.free_list_length);
        p.next = my_free_list;
        my_free_list = &t;
    } else if( p.origin && uintptr_t(p.origin) < uintptr_t(4096) ) {
        // a special value reserved for future use, do nothing since
        // origin is not pointing to a scheduler instance
    } else if( !(h&local_task) && p.origin ) {
        GATHER_STATISTIC(++my_counters.free_list_length);
#if __TBB_HOARD_NONLOCAL_TASKS
        p.next = my_nonlocal_free_list;
        my_nonlocal_free_list = &t;
#else
        free_nonlocal_small_task(t);
#endif
    } else {
        GATHER_STATISTIC(--my_counters.big_tasks);
        deallocate_task(t);
    }
}

#if __TBB_TASK_PRIORITY
inline bool generic_scheduler::worker_outermost_level () const {
    return !my_dispatching_task;
}

inline intptr_t generic_scheduler::effective_reference_priority () const {
    // Workers on the outermost dispatch level (i.e. with empty stack) use market's
    // priority as a reference point (to speedup discovering process level priority
    // changes). But when there are enough workers to service (even if only partially)
    // a lower priority arena, they should use arena's priority as a reference, lest
    // be trapped in a futile spinning (because market's priority would prohibit
    // executing ANY tasks in this arena).
    return !worker_outermost_level() || 
            my_arena->my_num_workers_allotted < my_arena->num_workers_active()
            ? *my_ref_top_priority : my_arena->my_top_priority;
}

inline void generic_scheduler::offload_task ( task& t, intptr_t /*priority*/ ) {
    GATHER_STATISTIC( ++my_counters.prio_tasks_offloaded );
    __TBB_ASSERT( my_offloaded_task_list_tail_link && !*my_offloaded_task_list_tail_link, NULL );
#if TBB_USE_ASSERT
    t.prefix().state = task::ready;
#endif /* TBB_USE_ASSERT */
    t.prefix().next_offloaded = my_offloaded_tasks;
    my_offloaded_tasks = &t;
}
#endif /* __TBB_TASK_PRIORITY */

} // namespace internal
} // namespace tbb

#endif /* _TBB_scheduler_H */
