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/*

 * Copyright (c) 2009 Martin Decky

 * All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 *

 * - Redistributions of source code must retain the above copyright

 *   notice, this list of conditions and the following disclaimer.

 * - Redistributions in binary form must reproduce the above copyright

 *   notice, this list of conditions and the following disclaimer in the

 *   documentation and/or other materials provided with the distribution.

 * - The name of the author may not be used to endorse or promote products

 *   derived from this software without specific prior written permission.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

/** @addtogroup ns

 * @{

 */

#include <ipc/ipc.h>

#include <adt/hash_table.h>

#include <bool.h>

#include <errno.h>

#include <assert.h>

#include <stdio.h>

#include <macros.h>

#include "task.h"

#include "ns.h"

#define TASK_HASH_TABLE_CHAINS  256

/* TODO:

 *

 * The current implementation of waiting on a task is not perfect. If somebody

 * wants to wait on a task which has already finished before the NS asked

 * the kernel to receive notifications, it would block indefinitively.

 *

 * A solution to this is to fail immediately on a task for which no creation

 * notification was received yet. However, there is a danger of a race condition

 * in this solution -- the caller has to make sure that it is not trying to wait

 * before the NS has a change to receive the task creation notification. This

 * can be assured by waiting for this event in task_spawn().

 *

 * Finally, as there is currently no convention that each task has to be waited

 * for, the NS can leak memory because of the zombie tasks.

 *

 */

/** Task hash table item. */

typedef struct {

    link_t link;

    task_id_t id;    /**< Task ID. */

    bool destroyed;

} hashed_task_t;

/** Compute hash index into task hash table.

 *

 * @param key Pointer keys. However, only the first key (i.e. truncated task

 *            number) is used to compute the hash index.

 *

 * @return Hash index corresponding to key[0].

 *

 */

static hash_index_t task_hash(unsigned long *key)

{

    assert(key);

    return (LOWER32(*key) % TASK_HASH_TABLE_CHAINS);

}

/** Compare a key with hashed item.

 *

 * @param key  Array of keys.

 * @param keys Must be lesser or equal to 2.

 * @param item Pointer to a hash table item.

 *

 * @return Non-zero if the key matches the item, zero otherwise.

 *

 */

static int task_compare(unsigned long key[], hash_count_t keys, link_t *item)

{

    assert(key);

    assert(keys <= 2);

    assert(item);

    hashed_task_t *ht = hash_table_get_instance(item, hashed_task_t, link);

    if (keys == 2)

        return ((LOWER32(key[1]) == UPPER32(ht->id))

            && (LOWER32(key[0]) == LOWER32(ht->id)));

    else

        return (LOWER32(key[0]) == LOWER32(ht->id));

}

/** Perform actions after removal of item from the hash table.

 *

 * @param item Item that was removed from the hash table.

 *

 */

static void task_remove(link_t *item)

{

    assert(item);

    free(hash_table_get_instance(item, hashed_task_t, link));

}

/** Operations for task hash table. */

static hash_table_operations_t task_hash_table_ops = {

    .hash = task_hash,

    .compare = task_compare,

    .remove_callback = task_remove

};

/** Task hash table structure. */

static hash_table_t task_hash_table;

/** Pending task wait structure. */

typedef struct {

    link_t link;

    task_id_t id;         /**< Task ID. */

    ipc_callid_t callid;  /**< Call ID waiting for the connection */

} pending_wait_t;

static link_t pending_wait;

int task_init(void)

{

    if (!hash_table_create(&task_hash_table, TASK_HASH_TABLE_CHAINS,

        2, &task_hash_table_ops)) {

        printf(NAME ": No memory available for tasks\n");

        return ENOMEM;

    }

    if (event_subscribe(EVENT_WAIT, 0) != EOK)

        printf(NAME ": Error registering wait notifications\n");

    list_initialize(&pending_wait);

    return EOK;

}

/** Process pending wait requests */

void process_pending_wait(void)

{

    link_t *cur;

loop:

    for (cur = pending_wait.next; cur != &pending_wait; cur = cur->next) {

        pending_wait_t *pr = list_get_instance(cur, pending_wait_t, link);

        unsigned long keys[2] = {

            LOWER32(pr->id),

            UPPER32(pr->id)

        };

        link_t *link = hash_table_find(&task_hash_table, keys);

        if (!link)

            continue;

        hashed_task_t *ht = hash_table_get_instance(link, hashed_task_t, link);

        if (!ht->destroyed)

            continue;

        if (!(pr->callid & IPC_CALLID_NOTIFICATION))

            ipc_answer_0(pr->callid, EOK);

        hash_table_remove(&task_hash_table, keys, 2);

        list_remove(cur);

        free(pr);

        goto loop;

    }

}

static void fail_pending_wait(task_id_t id, int rc)

{

    link_t *cur;

loop:

    for (cur = pending_wait.next; cur != &pending_wait; cur = cur->next) {

        pending_wait_t *pr = list_get_instance(cur, pending_wait_t, link);

        if (pr->id == id) {

            if (!(pr->callid & IPC_CALLID_NOTIFICATION))

                ipc_answer_0(pr->callid, rc);

            list_remove(cur);

            free(pr);

            goto loop;

        }

    }

}

void wait_notification(wait_type_t et, task_id_t id)

{

    unsigned long keys[2] = {

        LOWER32(id),

        UPPER32(id)

    };

    link_t *link = hash_table_find(&task_hash_table, keys);

    if (link == NULL) {

        hashed_task_t *ht =

            (hashed_task_t *) malloc(sizeof(hashed_task_t));

        if (ht == NULL) {

            fail_pending_wait(id, ENOMEM);

            return;

        }

        link_initialize(&ht->link);

        ht->id = id;

        ht->destroyed = (et == TASK_CREATE) ? false : true;

        hash_table_insert(&task_hash_table, keys, &ht->link);

    } else {

        hashed_task_t *ht =

            hash_table_get_instance(link, hashed_task_t, link);

        ht->destroyed = (et == TASK_CREATE) ? false : true;

    }

}

void wait_for_task(task_id_t id, ipc_call_t *call, ipc_callid_t callid)

{

    ipcarg_t retval;

    unsigned long keys[2] = {

        LOWER32(id),

        UPPER32(id)

    };

    link_t *link = hash_table_find(&task_hash_table, keys);

    hashed_task_t *ht = (link != NULL) ?

        hash_table_get_instance(link, hashed_task_t, link) : NULL;

    if ((ht == NULL) || (!ht->destroyed)) {

        /* Add to pending list */

        pending_wait_t *pr =

            (pending_wait_t *) malloc(sizeof(pending_wait_t));

        if (!pr) {

            retval = ENOMEM;

            goto out;

        }

        pr->id = id;

        pr->callid = callid;

        list_append(&pr->link, &pending_wait);

        return;

    }

    hash_table_remove(&task_hash_table, keys, 2);

    retval = EOK;

out:

    if (!(callid & IPC_CALLID_NOTIFICATION))

        ipc_answer_0(callid, retval);

}

/**

 * @}

 */