/*
    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_mailbox_H
#define _TBB_mailbox_H

#include "tbb/tbb_stddef.h"
#include "tbb/cache_aligned_allocator.h"

#include "scheduler_common.h"

namespace tbb {
namespace internal {

class generic_scheduler;
class mail_outbox;

struct task_proxy : public task {
    static const intptr_t      pool_bit = 1<<0;
    static const intptr_t   mailbox_bit = 1<<1;
    static const intptr_t location_mask = pool_bit | mailbox_bit;
    /* All but two low-order bits represent a (task*).
       Two low-order bits mean:
       1 = proxy is/was/will be in task pool
       2 = proxy is/was/will be in mailbox */
    intptr_t task_and_tag;

    //! Pointer to next task_proxy in a mailbox
    task_proxy *__TBB_atomic next_in_mailbox;

    //! Mailbox to which this was mailed.
    mail_outbox* outbox;

    //! True if the proxy is stored both in its sender's pool and in the destination mailbox.
    static bool is_shared ( intptr_t tat ) {
        return (tat & location_mask) == location_mask;
    }

    //! Returns a pointer to the encapsulated task or NULL.
    static task* task_ptr ( intptr_t tat ) {
        return (task*)(tat & ~location_mask);
    }

    //! Returns a pointer to the encapsulated task or NULL, and frees proxy if necessary.
    template<intptr_t from_bit>
    inline task* extract_task () {
        __TBB_ASSERT( prefix().extra_state == es_task_proxy, "Normal task misinterpreted as a proxy?" );
        intptr_t tat = __TBB_load_with_acquire(task_and_tag);
        __TBB_ASSERT( tat == from_bit || (is_shared(tat) && task_ptr(tat)),
            "Proxy's tag cannot specify both locations if the proxy "
            "was retrieved from one of its original locations" );
        if ( tat != from_bit ) {
            const intptr_t cleaner_bit = location_mask & ~from_bit;
            // Attempt to transition the proxy to the "empty" state with
            // cleaner_bit specifying entity responsible for its eventual freeing.
            // Explicit cast to void* is to work around a seeming ICC 11.1 bug.
            if ( __TBB_CompareAndSwapW( (void*)&task_and_tag, cleaner_bit, tat ) == tat ) {
                // Successfully grabbed the task, and left new owner with the job of freeing the proxy
                return task_ptr(tat);
            }
        }
        // Proxied task has already been claimed from another proxy location.
        __TBB_ASSERT( task_and_tag == from_bit, "Empty proxy cannot contain non-zero task pointer" );
        poison_pointer(outbox);
        poison_pointer(next_in_mailbox);
        poison_value(task_and_tag);
        return NULL;
    }
}; // struct task_proxy

//! Internal representation of mail_outbox, without padding.
class unpadded_mail_outbox {
protected:
    typedef task_proxy*__TBB_atomic proxy_ptr;

    //! Pointer to first task_proxy in mailbox, or NULL if box is empty. 
    proxy_ptr my_first;

    //! Pointer to pointer that will point to next item in the queue.  Never NULL.
    proxy_ptr* __TBB_atomic my_last;

    //! Owner of mailbox is not executing a task, and has drained its own task pool.
    bool my_is_idle;
};

//! Class representing where mail is put.
/** Padded to occupy a cache line. */
class mail_outbox : unpadded_mail_outbox {
    char pad[NFS_MaxLineSize-sizeof(unpadded_mail_outbox)];

    task_proxy* internal_pop() {
        task_proxy* const first = __TBB_load_relaxed(my_first);
        if( !first )
            return NULL;
        __TBB_control_consistency_helper(); // on my_first
        // There is a first item in the mailbox.  See if there is a second.
        if( task_proxy* second = first->next_in_mailbox ) {
            // There are at least two items, so first item can be popped easily.
            my_first = second;
        } else {
            // There is only one item.  Some care is required to pop it.
            my_first = NULL;
            if( (proxy_ptr*)__TBB_CompareAndSwapW(&my_last, (intptr_t)&my_first,
                                (intptr_t)&first->next_in_mailbox) == &first->next_in_mailbox )
            {
                // Successfully transitioned mailbox from having one item to having none.
                __TBB_ASSERT(!first->next_in_mailbox,NULL);
            } else {
                // Some other thread updated my_last but has not filled in first->next_in_mailbox
                // Wait until first item points to second item.
                for( atomic_backoff backoff; !(second = first->next_in_mailbox); backoff.pause() ) {}
                my_first = second;
            }
        }
        return first;
    }
public:
    friend class mail_inbox;

    //! Push task_proxy onto the mailbox queue of another thread.
    /** Implementation is wait-free. */
    void push( task_proxy& t ) {
        __TBB_ASSERT(&t, NULL);
        t.next_in_mailbox = NULL; 
        proxy_ptr * const link = (proxy_ptr *)__TBB_FetchAndStoreW(&my_last,(intptr_t)&t.next_in_mailbox);
        // No release fence required for the next store, because there are no memory operations 
        // between the previous fully fenced atomic operation and the store.
        __TBB_store_relaxed(*link, &t);
    }

    //! Construct *this as a mailbox from zeroed memory.
    /** Raise assertion if *this is not previously zeroed, or sizeof(this) is wrong.
        This method is provided instead of a full constructor since we know the object
        will be constructed in zeroed memory. */
    void construct() {
        __TBB_ASSERT( sizeof(*this)==NFS_MaxLineSize, NULL );
        __TBB_ASSERT( !my_first, NULL );
        __TBB_ASSERT( !my_last, NULL );
        __TBB_ASSERT( !my_is_idle, NULL );
        my_last=&my_first;
    }

    //! Drain the mailbox 
    intptr_t drain() {
        intptr_t k = 0;
        // No fences here because other threads have already quit.
        for( ; task_proxy* t = my_first; ++k ) {
            my_first = t->next_in_mailbox;
            NFS_Free((char*)t - task_prefix_reservation_size);
        }
        return k;  
    }

    //! True if thread that owns this mailbox is looking for work.
    bool recipient_is_idle() {
        return my_is_idle;
    }
}; // class mail_outbox

//! Class representing source of mail.
class mail_inbox {
    //! Corresponding sink where mail that we receive will be put.
    mail_outbox* my_putter;
public:
    //! Construct unattached inbox
    mail_inbox() : my_putter(NULL) {}

    //! Attach inbox to a corresponding outbox. 
    void attach( mail_outbox& putter ) {
        __TBB_ASSERT(!my_putter,"already attached");
        my_putter = &putter;
    }
    //! Detach inbox from its outbox
    void detach() {
        __TBB_ASSERT(my_putter,"not attached");
        my_putter = NULL;
    }
    //! Get next piece of mail, or NULL if mailbox is empty.
    task_proxy* pop() {
        return my_putter->internal_pop();
    }
    //! Indicate whether thread that reads this mailbox is idle.
    /** Raises assertion failure if mailbox is redundantly marked as not idle. */
    void set_is_idle( bool value ) {
        if( my_putter ) {
            __TBB_ASSERT( my_putter->my_is_idle || value, "attempt to redundantly mark mailbox as not idle" );
            my_putter->my_is_idle = value;
        }
    }
    //! Indicate whether thread that reads this mailbox is idle.
    bool is_idle_state ( bool value ) const {
        return !my_putter || my_putter->my_is_idle == value;
    }

#if DO_ITT_NOTIFY
    //! Get pointer to corresponding outbox used for ITT_NOTIFY calls.
    void* outbox() const {return my_putter;}
#endif /* DO_ITT_NOTIFY */ 
}; // class mail_inbox

} // namespace internal
} // namespace tbb

#endif /* _TBB_mailbox_H */
