/* 
 * Copyright (C) 2008-2011 Teluu Inc. (http://www.teluu.com)
 * Copyright (C) 2003-2008 Benny Prijono <benny@prijono.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 
 */

/*
 * sock_select.c
 *
 * This is the implementation of IOQueue using pj_sock_select().
 * It runs anywhere where pj_sock_select() is available (currently
 * Win32, Linux, Linux kernel, etc.).
 */

#include <pj/ioqueue.h>
#include <pj/os.h>
#include <pj/lock.h>
#include <pj/log.h>
#include <pj/list.h>
#include <pj/pool.h>
#include <pj/string.h>
#include <pj/assert.h>
#include <pj/sock.h>
#include <pj/compat/socket.h>
#include <pj/sock_select.h>
#include <pj/sock_qos.h>
#include <pj/errno.h>
#include <pj/rand.h>

/* Now that we have access to OS'es <sys/select>, lets check again that
 * PJ_IOQUEUE_MAX_HANDLES is not greater than FD_SETSIZE
 */
#if PJ_IOQUEUE_MAX_HANDLES > FD_SETSIZE
#   error "PJ_IOQUEUE_MAX_HANDLES cannot be greater than FD_SETSIZE"
#endif


/*
 * Include declaration from common abstraction.
 */
#include "ioqueue_common_abs.h"

/*
 * ISSUES with ioqueue_select()
 *
 * EAGAIN/EWOULDBLOCK error in recv():
 *  - when multiple threads are working with the ioqueue, application
 *    may receive EAGAIN or EWOULDBLOCK in the receive callback.
 *    This error happens because more than one thread is watching for
 *    the same descriptor set, so when all of them call recv() or recvfrom()
 *    simultaneously, only one will succeed and the rest will get the error.
 *
 */
#define THIS_FILE   "ioq_select"

/*
 * The select ioqueue relies on socket functions (pj_sock_xxx()) to return
 * the correct error code.
 */
#if PJ_RETURN_OS_ERROR(100) != PJ_STATUS_FROM_OS(100)
#   error "Error reporting must be enabled for this function to work!"
#endif

/*
 * During debugging build, VALIDATE_FD_SET is set.
 * This will check the validity of the fd_sets.
 */
/*
#if defined(PJ_DEBUG) && PJ_DEBUG != 0
#  define VALIDATE_FD_SET               1
#else
#  define VALIDATE_FD_SET               0
#endif
*/
#define VALIDATE_FD_SET     0

#if 0
#  define TRACE__(args) PJ_LOG(3,args)
#else
#  define TRACE__(args)
#endif

/*
 * This describes each key.
 */
struct pj_ioqueue_key_t
{
    DECLARE_COMMON_KEY
};

/*
 * This describes the I/O queue itself.
 */
struct pj_ioqueue_t
{
    DECLARE_COMMON_IOQUEUE

    unsigned            max, count;     /* Max and current key count        */
    int                 nfds;           /* The largest fd value (for select)*/
    pj_ioqueue_key_t    active_list;    /* List of active keys.             */
    pj_fd_set_t         rfdset;
    pj_fd_set_t         wfdset;
#if PJ_HAS_TCP
    pj_fd_set_t         xfdset;
#endif

#if PJ_IOQUEUE_HAS_SAFE_UNREG
    pj_mutex_t         *ref_cnt_mutex;
    pj_ioqueue_key_t    closing_list;
    pj_ioqueue_key_t    free_list;
#endif
};

/* Proto */
#if defined(PJ_IPHONE_OS_HAS_MULTITASKING_SUPPORT) && \
            PJ_IPHONE_OS_HAS_MULTITASKING_SUPPORT!=0
static pj_status_t replace_udp_sock(pj_ioqueue_key_t *h);
#endif

#if defined(PJ_HAS_SSL_SOCK) && PJ_HAS_SSL_SOCK != 0 && \
    (PJ_SSL_SOCK_IMP == PJ_SSL_SOCK_IMP_APPLE)
    /* Call SSL Network framework poll */
pj_status_t ssl_network_event_poll();
#endif

/* Include implementation for common abstraction after we declare
 * pj_ioqueue_key_t and pj_ioqueue_t.
 */
#include "ioqueue_common_abs.c"

#if PJ_IOQUEUE_HAS_SAFE_UNREG
/* Scan closing keys to be put to free list again */
static void scan_closing_keys(pj_ioqueue_t *ioqueue);
#endif

/*
 * pj_ioqueue_name()
 */
PJ_DEF(const char*) pj_ioqueue_name(void)
{
    return "select";
}

/* 
 * Scan the socket descriptor sets for the largest descriptor.
 * This value is needed by select().
 */
#if defined(PJ_SELECT_NEEDS_NFDS) && PJ_SELECT_NEEDS_NFDS!=0
static void rescan_fdset(pj_ioqueue_t *ioqueue)
{
    pj_ioqueue_key_t *key = ioqueue->active_list.next;
    int max = 0;

    while (key != &ioqueue->active_list) {
        if (key->fd > max)
            max = key->fd;
        key = key->next;
    }

    ioqueue->nfds = max;
}
#else
static void rescan_fdset(pj_ioqueue_t *ioqueue)
{
    ioqueue->nfds = FD_SETSIZE-1;
}
#endif


/*
 * pj_ioqueue_create()
 *
 * Create select ioqueue.
 */
PJ_DEF(pj_status_t) pj_ioqueue_create( pj_pool_t *pool,
                                       pj_size_t max_fd,
                                       pj_ioqueue_t **p_ioqueue)
{
    return pj_ioqueue_create2(pool, max_fd, NULL, p_ioqueue);
}


/*
 * pj_ioqueue_create2()
 *
 * Create select ioqueue.
 */
PJ_DEF(pj_status_t) pj_ioqueue_create2(pj_pool_t *pool,
                                       pj_size_t max_fd,
                                       const pj_ioqueue_cfg *cfg,
                                       pj_ioqueue_t **p_ioqueue)
{
    pj_ioqueue_t *ioqueue;
    pj_lock_t *lock;
    unsigned i;
    pj_status_t rc;

    /* Check that arguments are valid. */
    PJ_ASSERT_RETURN(pool != NULL && p_ioqueue != NULL && 
                     max_fd > 0 && max_fd <= PJ_IOQUEUE_MAX_HANDLES, 
                     PJ_EINVAL);

    /* Check that size of pj_ioqueue_op_key_t is sufficient */
    PJ_ASSERT_RETURN(sizeof(pj_ioqueue_op_key_t)-sizeof(void*) >=
                     sizeof(union operation_key), PJ_EBUG);

    /* Create and init common ioqueue stuffs */
    ioqueue = PJ_POOL_ALLOC_T(pool, pj_ioqueue_t);
    ioqueue_init(ioqueue);

    if (cfg)
        pj_memcpy(&ioqueue->cfg, cfg, sizeof(*cfg));
    else
        pj_ioqueue_cfg_default(&ioqueue->cfg);
    ioqueue->max = (unsigned)max_fd;
    ioqueue->count = 0;
    PJ_FD_ZERO(&ioqueue->rfdset);
    PJ_FD_ZERO(&ioqueue->wfdset);
#if PJ_HAS_TCP
    PJ_FD_ZERO(&ioqueue->xfdset);
#endif
    pj_list_init(&ioqueue->active_list);

    rescan_fdset(ioqueue);

#if PJ_IOQUEUE_HAS_SAFE_UNREG
    /* When safe unregistration is used (the default), we pre-create
     * all keys and put them in the free list.
     */

    /* Mutex to protect key's reference counter 
     * We don't want to use key's mutex or ioqueue's mutex because
     * that would create deadlock situation in some cases.
     */
    rc = pj_mutex_create_simple(pool, NULL, &ioqueue->ref_cnt_mutex);
    if (rc != PJ_SUCCESS)
        return rc;


    /* Init key list */
    pj_list_init(&ioqueue->free_list);
    pj_list_init(&ioqueue->closing_list);


    /* Pre-create all keys according to max_fd */
    for (i=0; i<max_fd; ++i) {
        pj_ioqueue_key_t *key;

        key = PJ_POOL_ALLOC_T(pool, pj_ioqueue_key_t);
        key->ref_count = 0;
        rc = pj_lock_create_recursive_mutex(pool, NULL, &key->lock);
        if (rc != PJ_SUCCESS) {
            key = ioqueue->free_list.next;
            while (key != &ioqueue->free_list) {
                pj_lock_destroy(key->lock);
                key = key->next;
            }
            pj_mutex_destroy(ioqueue->ref_cnt_mutex);
            return rc;
        }

        pj_list_push_back(&ioqueue->free_list, key);
    }
#endif

    /* Create and init ioqueue mutex */
    rc = pj_lock_create_simple_mutex(pool, "ioq%p", &lock);
    if (rc != PJ_SUCCESS)
        return rc;

    rc = pj_ioqueue_set_lock(ioqueue, lock, PJ_TRUE);
    if (rc != PJ_SUCCESS)
        return rc;

    PJ_LOG(4, ("pjlib", "select() I/O Queue created (%p)", ioqueue));

    *p_ioqueue = ioqueue;
    return PJ_SUCCESS;
}

/*
 * pj_ioqueue_destroy()
 *
 * Destroy ioqueue.
 */
PJ_DEF(pj_status_t) pj_ioqueue_destroy(pj_ioqueue_t *ioqueue)
{
    pj_ioqueue_key_t *key;

    PJ_ASSERT_RETURN(ioqueue, PJ_EINVAL);

    pj_lock_acquire(ioqueue->lock);

#if PJ_IOQUEUE_HAS_SAFE_UNREG
    /* Destroy reference counters */
    key = ioqueue->active_list.next;
    while (key != &ioqueue->active_list) {
        pj_lock_destroy(key->lock);
        key = key->next;
    }

    key = ioqueue->closing_list.next;
    while (key != &ioqueue->closing_list) {
        pj_lock_destroy(key->lock);
        key = key->next;
    }

    key = ioqueue->free_list.next;
    while (key != &ioqueue->free_list) {
        pj_lock_destroy(key->lock);
        key = key->next;
    }

    pj_mutex_destroy(ioqueue->ref_cnt_mutex);
#endif

    return ioqueue_destroy(ioqueue);
}


/*
 * pj_ioqueue_register_sock()
 *
 * Register socket handle to ioqueue.
 */
PJ_DEF(pj_status_t) pj_ioqueue_register_sock2(pj_pool_t *pool,
                                              pj_ioqueue_t *ioqueue,
                                              pj_sock_t sock,
                                              pj_grp_lock_t *grp_lock,
                                              void *user_data,
                                              const pj_ioqueue_callback *cb,
                                              pj_ioqueue_key_t **p_key)
{
    pj_ioqueue_key_t *key = NULL;
#if defined(PJ_WIN32) && PJ_WIN32!=0 || \
    defined(PJ_WIN64) && PJ_WIN64 != 0 || \
    defined(PJ_WIN32_WINCE) && PJ_WIN32_WINCE!=0
    u_long value;
#else
    pj_uint32_t value;
#endif
    pj_status_t rc = PJ_SUCCESS;
    
    PJ_ASSERT_RETURN(pool && ioqueue && sock != PJ_INVALID_SOCKET &&
                     cb && p_key, PJ_EINVAL);

    /* On platforms with fd_set containing fd bitmap such as *nix family,
     * avoid potential memory corruption caused by select() when given
     * an fd that is higher than FD_SETSIZE.
     */
    if (sizeof(fd_set) < FD_SETSIZE && sock >= FD_SETSIZE) {
        PJ_LOG(4, ("pjlib", "Failed to register socket to ioqueue because "
                            "socket fd is too big (fd=%d/FD_SETSIZE=%d)",
                            sock, FD_SETSIZE));
        return PJ_ETOOBIG;
    }

    pj_lock_acquire(ioqueue->lock);

    if (ioqueue->count >= ioqueue->max) {
        rc = PJ_ETOOMANY;
        goto on_return;
    }

    /* If safe unregistration (PJ_IOQUEUE_HAS_SAFE_UNREG) is used, get
     * the key from the free list. Otherwise allocate a new one. 
     */
#if PJ_IOQUEUE_HAS_SAFE_UNREG

    /* Scan closing_keys first to let them come back to free_list */
    scan_closing_keys(ioqueue);

    pj_assert(!pj_list_empty(&ioqueue->free_list));
    if (pj_list_empty(&ioqueue->free_list)) {
        rc = PJ_ETOOMANY;
        goto on_return;
    }

    key = ioqueue->free_list.next;
    pj_list_erase(key);
#else
    key = (pj_ioqueue_key_t*)pj_pool_zalloc(pool, sizeof(pj_ioqueue_key_t));
#endif

    rc = ioqueue_init_key(pool, ioqueue, key, sock, grp_lock, user_data, cb);
    if (rc != PJ_SUCCESS) {
        key = NULL;
        goto on_return;
    }

    /* Set socket to nonblocking. */
    value = 1;
#if defined(PJ_WIN32) && PJ_WIN32!=0 || \
    defined(PJ_WIN64) && PJ_WIN64 != 0 || \
    defined(PJ_WIN32_WINCE) && PJ_WIN32_WINCE!=0
    if (ioctlsocket(sock, FIONBIO, &value)) {
#else
    if (ioctl(sock, FIONBIO, &value)) {
#endif
        rc = pj_get_netos_error();
        goto on_return;
    }


    /* Put in active list. */
    pj_list_insert_before(&ioqueue->active_list, key);
    ++ioqueue->count;

    /* Rescan fdset to get max descriptor */
    rescan_fdset(ioqueue);

on_return:
    /* On error, socket may be left in non-blocking mode. */
    if (rc != PJ_SUCCESS) {
        if (key && key->grp_lock)
            pj_grp_lock_dec_ref_dbg(key->grp_lock, "ioqueue", 0);
    }
    *p_key = key;
    pj_lock_release(ioqueue->lock);
    
    return rc;
}

PJ_DEF(pj_status_t) pj_ioqueue_register_sock( pj_pool_t *pool,
                                              pj_ioqueue_t *ioqueue,
                                              pj_sock_t sock,
                                              void *user_data,
                                              const pj_ioqueue_callback *cb,
                                              pj_ioqueue_key_t **p_key)
{
    return pj_ioqueue_register_sock2(pool, ioqueue, sock, NULL, user_data,
                                     cb, p_key);
}

#if PJ_IOQUEUE_HAS_SAFE_UNREG
/* Increment key's reference counter */
static void increment_counter(pj_ioqueue_key_t *key)
{
    pj_mutex_lock(key->ioqueue->ref_cnt_mutex);
    ++key->ref_count;
    pj_mutex_unlock(key->ioqueue->ref_cnt_mutex);
}

/* Decrement the key's reference counter, and when the counter reach zero,
 * destroy the key.
 *
 * Note: MUST NOT CALL THIS FUNCTION WHILE HOLDING ioqueue's LOCK.
 */
static void decrement_counter(pj_ioqueue_key_t *key)
{
    pj_lock_acquire(key->ioqueue->lock);
    pj_mutex_lock(key->ioqueue->ref_cnt_mutex);
    --key->ref_count;
    if (key->ref_count == 0) {

        pj_assert(key->closing == 1);
        pj_gettickcount(&key->free_time);
        key->free_time.msec += PJ_IOQUEUE_KEY_FREE_DELAY;
        pj_time_val_normalize(&key->free_time);

        pj_list_erase(key);
        pj_list_push_back(&key->ioqueue->closing_list, key);
        /* Rescan fdset to get max descriptor */
        rescan_fdset(key->ioqueue);
    }
    pj_mutex_unlock(key->ioqueue->ref_cnt_mutex);
    pj_lock_release(key->ioqueue->lock);
}
#endif


/*
 * pj_ioqueue_unregister()
 *
 * Unregister handle from ioqueue.
 */
PJ_DEF(pj_status_t) pj_ioqueue_unregister( pj_ioqueue_key_t *key)
{
    pj_ioqueue_t *ioqueue;

    PJ_ASSERT_RETURN(key, PJ_EINVAL);

    ioqueue = key->ioqueue;

    /* Lock the key to make sure no callback is simultaneously modifying
     * the key. We need to lock the key before ioqueue here to prevent
     * deadlock.
     */
    pj_ioqueue_lock_key(key);

    /* Best effort to avoid double key-unregistration */
    if (IS_CLOSING(key)) {
        pj_ioqueue_unlock_key(key);
        return PJ_SUCCESS;
    }

    /* Also lock ioqueue */
    pj_lock_acquire(ioqueue->lock);

    /* Avoid "negative" ioqueue count */
    if (ioqueue->count > 0) {
        --ioqueue->count;
    } else {
        /* If this happens, very likely there is double unregistration
         * of a key.
         */
        pj_assert(!"Bad ioqueue count in key unregistration!");
        PJ_LOG(1,(THIS_FILE, "Bad ioqueue count in key unregistration!"));
    }

#if !PJ_IOQUEUE_HAS_SAFE_UNREG
    /* Ticket #520, key will be erased more than once */
    pj_list_erase(key);
#endif

    /* Remove socket from sets and close socket. */
    if (key->fd != PJ_INVALID_SOCKET) {
        PJ_FD_CLR(key->fd, &ioqueue->rfdset);
        PJ_FD_CLR(key->fd, &ioqueue->wfdset);
#if PJ_HAS_TCP
        PJ_FD_CLR(key->fd, &ioqueue->xfdset);
#endif

        pj_sock_close(key->fd);
        key->fd = PJ_INVALID_SOCKET;
    }

    /* Clear callback */
    key->cb.on_accept_complete = NULL;
    key->cb.on_connect_complete = NULL;
    key->cb.on_read_complete = NULL;
    key->cb.on_write_complete = NULL;

    /* Must release ioqueue lock first before decrementing counter, to
     * prevent deadlock.
     */
    pj_lock_release(ioqueue->lock);

#if PJ_IOQUEUE_HAS_SAFE_UNREG
    /* Mark key is closing. */
    key->closing = 1;

    /* Decrement counter. */
    decrement_counter(key);

    /* Done. */
    if (key->grp_lock) {
        /* just dec_ref and unlock. we will set grp_lock to NULL
         * elsewhere */
        pj_grp_lock_t *grp_lock = key->grp_lock;
        // Don't set grp_lock to NULL otherwise the other thread
        // will crash. Just leave it as dangling pointer, but this
        // should be safe
        //key->grp_lock = NULL;
        pj_grp_lock_dec_ref_dbg(grp_lock, "ioqueue", 0);
        pj_grp_lock_release(grp_lock);
    } else {
        pj_ioqueue_unlock_key(key);
    }
#else
    if (key->grp_lock) {
        /* set grp_lock to NULL and unlock */
        pj_grp_lock_t *grp_lock = key->grp_lock;
        // Don't set grp_lock to NULL otherwise the other thread
        // will crash. Just leave it as dangling pointer, but this
        // should be safe
        //key->grp_lock = NULL;
        pj_grp_lock_dec_ref_dbg(grp_lock, "ioqueue", 0);
        pj_grp_lock_release(grp_lock);
    } else {
        pj_ioqueue_unlock_key(key);
    }

    pj_lock_destroy(key->lock);
#endif

    return PJ_SUCCESS;
}


/* This supposed to check whether the fd_set values are consistent
 * with the operation currently set in each key.
 */
#if VALIDATE_FD_SET
static void validate_sets(const pj_ioqueue_t *ioqueue,
                          const pj_fd_set_t *rfdset,
                          const pj_fd_set_t *wfdset,
                          const pj_fd_set_t *xfdset)
{
    pj_ioqueue_key_t *key;

    /*
     * This basicly would not work anymore.
     * We need to lock key before performing the check, but we can't do
     * so because we're holding ioqueue mutex. If we acquire key's mutex
     * now, the will cause deadlock.
     */
    pj_assert(0);

    key = ioqueue->active_list.next;
    while (key != &ioqueue->active_list) {
        if (!pj_list_empty(&key->read_list)
#if defined(PJ_HAS_TCP) && PJ_HAS_TCP != 0
            || !pj_list_empty(&key->accept_list)
#endif
            ) 
        {
            pj_assert(PJ_FD_ISSET(key->fd, rfdset));
        } 
        else {
            pj_assert(PJ_FD_ISSET(key->fd, rfdset) == 0);
        }
        if (!pj_list_empty(&key->write_list)
#if defined(PJ_HAS_TCP) && PJ_HAS_TCP != 0
            || key->connecting
#endif
           )
        {
            pj_assert(PJ_FD_ISSET(key->fd, wfdset));
        }
        else {
            pj_assert(PJ_FD_ISSET(key->fd, wfdset) == 0);
        }
#if defined(PJ_HAS_TCP) && PJ_HAS_TCP != 0
        if (key->connecting)
        {
            pj_assert(PJ_FD_ISSET(key->fd, xfdset));
        }
        else {
            pj_assert(PJ_FD_ISSET(key->fd, xfdset) == 0);
        }
#endif /* PJ_HAS_TCP */

        key = key->next;
    }
}
#endif  /* VALIDATE_FD_SET */


/* ioqueue_remove_from_set()
 * This function is called from ioqueue_dispatch_event() to instruct
 * the ioqueue to remove the specified descriptor from ioqueue's descriptor
 * set for the specified event.
 */
static void ioqueue_remove_from_set( pj_ioqueue_t *ioqueue,
                                     pj_ioqueue_key_t *key,
                                     enum ioqueue_event_type event_type )
{
    ioqueue_remove_from_set2(ioqueue, key, event_type);
}

static void ioqueue_remove_from_set2(pj_ioqueue_t *ioqueue,
                                     pj_ioqueue_key_t *key, 
                                     unsigned event_types)
{
    pj_lock_acquire(ioqueue->lock);

    if (event_types & READABLE_EVENT)
        PJ_FD_CLR((pj_sock_t)key->fd, &ioqueue->rfdset);
    if (event_types & WRITEABLE_EVENT)
        PJ_FD_CLR((pj_sock_t)key->fd, &ioqueue->wfdset);
#if defined(PJ_HAS_TCP) && PJ_HAS_TCP!=0
    if (event_types & EXCEPTION_EVENT)
        PJ_FD_CLR((pj_sock_t)key->fd, &ioqueue->xfdset);
#endif

    pj_lock_release(ioqueue->lock);
}

/*
 * ioqueue_add_to_set()
 * This function is called from pj_ioqueue_recv(), pj_ioqueue_send() etc
 * to instruct the ioqueue to add the specified handle to ioqueue's descriptor
 * set for the specified event.
 */
static void ioqueue_add_to_set( pj_ioqueue_t *ioqueue,
                                pj_ioqueue_key_t *key,
                                enum ioqueue_event_type event_type )
{
    ioqueue_add_to_set2(ioqueue, key, event_type);
}

static void ioqueue_add_to_set2(pj_ioqueue_t *ioqueue,
                                pj_ioqueue_key_t *key,
                                unsigned event_types )
{
    pj_lock_acquire(ioqueue->lock);

    if (event_types & READABLE_EVENT)
        PJ_FD_SET((pj_sock_t)key->fd, &ioqueue->rfdset);
    if (event_types & WRITEABLE_EVENT)
        PJ_FD_SET((pj_sock_t)key->fd, &ioqueue->wfdset);
#if defined(PJ_HAS_TCP) && PJ_HAS_TCP!=0
    if (event_types & EXCEPTION_EVENT)
        PJ_FD_SET((pj_sock_t)key->fd, &ioqueue->xfdset);
#endif

    pj_lock_release(ioqueue->lock);
}

#if PJ_IOQUEUE_HAS_SAFE_UNREG
/* Scan closing keys to be put to free list again */
static void scan_closing_keys(pj_ioqueue_t *ioqueue)
{
    pj_time_val now;
    pj_ioqueue_key_t *h;

    pj_gettickcount(&now);
    h = ioqueue->closing_list.next;
    while (h != &ioqueue->closing_list) {
        pj_ioqueue_key_t *next = h->next;

        pj_assert(h->closing != 0);

        if (PJ_TIME_VAL_GTE(now, h->free_time)) {
            pj_list_erase(h);
            // Don't set grp_lock to NULL otherwise the other thread
            // will crash. Just leave it as dangling pointer, but this
            // should be safe
            //h->grp_lock = NULL;
            pj_list_push_back(&ioqueue->free_list, h);
        }
        h = next;
    }
}
#endif

#if defined(PJ_IPHONE_OS_HAS_MULTITASKING_SUPPORT) && \
    PJ_IPHONE_OS_HAS_MULTITASKING_SUPPORT!=0
static pj_status_t replace_udp_sock(pj_ioqueue_key_t *h)
{
    enum flags {
        HAS_PEER_ADDR = 1,
        HAS_QOS = 2
    };
    pj_sock_t old_sock, new_sock = PJ_INVALID_SOCKET;
    pj_sockaddr local_addr, rem_addr;
    int val, addr_len;
    pj_fd_set_t *fds[3];
    unsigned i, fds_cnt, flags=0;
    pj_qos_params qos_params;
    unsigned msec;
    pj_status_t status = PJ_EUNKNOWN;

    pj_lock_acquire(h->ioqueue->lock);

    old_sock = h->fd;

    fds_cnt = 0;
    fds[fds_cnt++] = &h->ioqueue->rfdset;
    fds[fds_cnt++] = &h->ioqueue->wfdset;
#if PJ_HAS_TCP
    fds[fds_cnt++] = &h->ioqueue->xfdset;
#endif

    /* Can only replace UDP socket */
    pj_assert(h->fd_type == pj_SOCK_DGRAM());

    PJ_LOG(4,(THIS_FILE, "Attempting to replace UDP socket %d", old_sock));

    for (msec=20; (msec<1000 && status != PJ_SUCCESS) ;
         msec<1000? msec=msec*2 : 1000)
    {
        if (msec > 20) {
            PJ_LOG(4,(THIS_FILE, "Retry to replace UDP socket %d", old_sock));
            pj_thread_sleep(msec);
        }
        
        if (old_sock != PJ_INVALID_SOCKET) {
            /* Investigate the old socket */
            addr_len = sizeof(local_addr);
            status = pj_sock_getsockname(old_sock, &local_addr, &addr_len);
            if (status != PJ_SUCCESS) {
                PJ_PERROR(5,(THIS_FILE, status, "Error get socket name"));
                continue;
            }
        
            addr_len = sizeof(rem_addr);
            status = pj_sock_getpeername(old_sock, &rem_addr, &addr_len);
            if (status != PJ_SUCCESS) {
                PJ_PERROR(5,(THIS_FILE, status, "Error get peer name"));
            } else {
                flags |= HAS_PEER_ADDR;
            }

            status = pj_sock_get_qos_params(old_sock, &qos_params);
            if (status == PJ_STATUS_FROM_OS(EBADF) ||
                status == PJ_STATUS_FROM_OS(EINVAL))
            {
                PJ_PERROR(5,(THIS_FILE, status, "Error get qos param"));
                continue;
            }
        
            if (status != PJ_SUCCESS) {
                PJ_PERROR(5,(THIS_FILE, status, "Error get qos param"));
            } else {
                flags |= HAS_QOS;
            }

            /* We're done with the old socket, close it otherwise we'll get
             * error in bind()
             */
            status = pj_sock_close(old_sock);
            if (status != PJ_SUCCESS) {
                PJ_PERROR(5,(THIS_FILE, status, "Error closing socket"));
            }
            
            old_sock = PJ_INVALID_SOCKET;
        }

        /* Prepare the new socket */
        status = pj_sock_socket(local_addr.addr.sa_family, PJ_SOCK_DGRAM, 0,
                                &new_sock);
        if (status != PJ_SUCCESS) {
            PJ_PERROR(5,(THIS_FILE, status, "Error create socket"));
            continue;
        }

        /* Even after the socket is closed, we'll still get "Address in use"
         * errors, so force it with SO_REUSEADDR
         */
        val = 1;
        status = pj_sock_setsockopt(new_sock, SOL_SOCKET, SO_REUSEADDR,
                                    &val, sizeof(val));
        if (status == PJ_STATUS_FROM_OS(EBADF) ||
            status == PJ_STATUS_FROM_OS(EINVAL))
        {
            PJ_PERROR(5,(THIS_FILE, status, "Error set socket option"));
            continue;
        }

        /* The loop is silly, but what else can we do? */
        addr_len = pj_sockaddr_get_len(&local_addr);
        for (msec=20; msec<1000 ; msec<1000? msec=msec*2 : 1000) {
            status = pj_sock_bind(new_sock, &local_addr, addr_len);
            if (status != PJ_STATUS_FROM_OS(EADDRINUSE))
                break;
            PJ_LOG(4,(THIS_FILE, "Address is still in use, retrying.."));
            pj_thread_sleep(msec);
        }

        if (status != PJ_SUCCESS)
            continue;

        if (flags & HAS_QOS) {
            status = pj_sock_set_qos_params(new_sock, &qos_params);
            if (status == PJ_STATUS_FROM_OS(EINVAL)) {
                PJ_PERROR(5,(THIS_FILE, status, "Error set qos param"));
                continue;
            }
        }

        if (flags & HAS_PEER_ADDR) {
            status = pj_sock_connect(new_sock, &rem_addr, addr_len);
            if (status != PJ_SUCCESS) {
                PJ_PERROR(5,(THIS_FILE, status, "Error connect socket"));
                continue;
            }
        }
    }
    
    if (status != PJ_SUCCESS)
        goto on_error;
    
    /* Set socket to nonblocking. */
    val = 1;
#if defined(PJ_WIN32) && PJ_WIN32!=0 || \
    defined(PJ_WIN64) && PJ_WIN64 != 0 || \
    defined(PJ_WIN32_WINCE) && PJ_WIN32_WINCE!=0
    if (ioctlsocket(new_sock, FIONBIO, &val)) {
#else
    if (ioctl(new_sock, FIONBIO, &val)) {
#endif
        status = pj_get_netos_error();
        goto on_error;
    }

    /* Replace the occurrence of old socket with new socket in the
     * fd sets.
     */
    for (i=0; i<fds_cnt; ++i) {
        if (PJ_FD_ISSET(h->fd, fds[i])) {
            PJ_FD_CLR(h->fd, fds[i]);
            PJ_FD_SET(new_sock, fds[i]);
        }
    }

    /* And finally replace the fd in the key */
    h->fd = new_sock;

    PJ_LOG(4,(THIS_FILE, "UDP has been replaced successfully!"));

    pj_lock_release(h->ioqueue->lock);

    return PJ_SUCCESS;

on_error:
    if (new_sock != PJ_INVALID_SOCKET)
        pj_sock_close(new_sock);
    if (old_sock != PJ_INVALID_SOCKET)
        pj_sock_close(old_sock);

    /* Clear the occurrence of old socket in the fd sets. */
    for (i=0; i<fds_cnt; ++i) {
        if (PJ_FD_ISSET(h->fd, fds[i])) {
            PJ_FD_CLR(h->fd, fds[i]);
        }
    }

    h->fd = PJ_INVALID_SOCKET;
    PJ_PERROR(1,(THIS_FILE, status, "Error replacing socket %d", old_sock));
    pj_lock_release(h->ioqueue->lock);
    return PJ_ESOCKETSTOP;
}
#endif


/*
 * pj_ioqueue_poll()
 *
 * Few things worth written:
 *
 *  - we used to do only one callback called per poll, but it didn't go
 *    very well. The reason is because on some situation, the write 
 *    callback gets called all the time, thus doesn't give the read
 *    callback to get called. This happens, for example, when user
 *    submit write operation inside the write callback.
 *    As the result, we changed the behaviour so that now multiple
 *    callbacks are called in a single poll. It should be fast too,
 *    just that we need to be carefull with the ioqueue data structs.
 *
 *  - to guarantee preemptiveness etc, the poll function must strictly
 *    work on fd_set copy of the ioqueue (not the original one).
 */
PJ_DEF(int) pj_ioqueue_poll( pj_ioqueue_t *ioqueue, const pj_time_val *timeout)
{
    pj_fd_set_t rfdset, wfdset, xfdset;
    int nfds;
    int i, count, event_cnt, processed_cnt;
    pj_ioqueue_key_t *h;
    enum { MAX_EVENTS = PJ_IOQUEUE_MAX_CAND_EVENTS };
    struct event
    {
        pj_ioqueue_key_t        *key;
        enum ioqueue_event_type  event_type;
    } event[MAX_EVENTS];

    PJ_ASSERT_RETURN(ioqueue, -PJ_EINVAL);

#if defined(PJ_HAS_SSL_SOCK) && PJ_HAS_SSL_SOCK != 0 && \
    (PJ_SSL_SOCK_IMP == PJ_SSL_SOCK_IMP_APPLE)
    /* Call SSL Network framework event poll */
    ssl_network_event_poll();
#endif

    /* Lock ioqueue before making fd_set copies */
    pj_lock_acquire(ioqueue->lock);

    /* We will only do select() when there are sockets to be polled.
     * Otherwise select() will return error.
     */
    if (PJ_FD_COUNT(&ioqueue->rfdset)==0 &&
        PJ_FD_COUNT(&ioqueue->wfdset)==0 
#if defined(PJ_HAS_TCP) && PJ_HAS_TCP!=0
        && PJ_FD_COUNT(&ioqueue->xfdset)==0
#endif
        )
    {
#if PJ_IOQUEUE_HAS_SAFE_UNREG
        scan_closing_keys(ioqueue);
#endif
        pj_lock_release(ioqueue->lock);
        TRACE__((THIS_FILE, "     poll: no fd is set"));
        if (timeout)
            pj_thread_sleep(PJ_TIME_VAL_MSEC(*timeout));
        return 0;
    }

    /* Copy ioqueue's pj_fd_set_t to local variables. */
    pj_memcpy(&rfdset, &ioqueue->rfdset, sizeof(pj_fd_set_t));
    pj_memcpy(&wfdset, &ioqueue->wfdset, sizeof(pj_fd_set_t));
#if PJ_HAS_TCP
    pj_memcpy(&xfdset, &ioqueue->xfdset, sizeof(pj_fd_set_t));
#else
    PJ_FD_ZERO(&xfdset);
#endif

#if VALIDATE_FD_SET
    validate_sets(ioqueue, &rfdset, &wfdset, &xfdset);
#endif

    nfds = ioqueue->nfds;

    /* Unlock ioqueue before select(). */
    pj_lock_release(ioqueue->lock);

#if defined(PJ_WIN32_WINPHONE8) && PJ_WIN32_WINPHONE8
    count = 0;
    __try {
#endif

    count = pj_sock_select(nfds+1, &rfdset, &wfdset, &xfdset, 
                           timeout);

#if defined(PJ_WIN32_WINPHONE8) && PJ_WIN32_WINPHONE8
    /* Ignore Invalid Handle Exception raised by select().*/
    }
    __except (GetExceptionCode() == STATUS_INVALID_HANDLE ?
              EXCEPTION_CONTINUE_EXECUTION : EXCEPTION_CONTINUE_SEARCH) {
    }
#endif    
    
    if (count == 0)
        return 0;
    else if (count < 0)
        return -pj_get_netos_error();

    /* Scan descriptor sets for event and add the events in the event
     * array to be processed later in this function. We do this so that
     * events can be processed in parallel without holding ioqueue lock.
     */
    pj_lock_acquire(ioqueue->lock);

    event_cnt = 0;

    /* Scan for writable sockets first to handle piggy-back data
     * coming with accept().
     */
    for (h = ioqueue->active_list.next;
         h != &ioqueue->active_list && event_cnt < MAX_EVENTS;
         h = h->next)
    {
        if (h->fd == PJ_INVALID_SOCKET)
            continue;

        if ( (key_has_pending_write(h) || key_has_pending_connect(h))
             && PJ_FD_ISSET(h->fd, &wfdset) && !IS_CLOSING(h))
        {
#if PJ_IOQUEUE_HAS_SAFE_UNREG
            increment_counter(h);
#endif
            event[event_cnt].key = h;
            event[event_cnt].event_type = WRITEABLE_EVENT;
            ++event_cnt;
        }

        /* Scan for readable socket. */
        if ((key_has_pending_read(h) || key_has_pending_accept(h))
            && PJ_FD_ISSET(h->fd, &rfdset) && !IS_CLOSING(h) &&
            event_cnt < MAX_EVENTS)
        {
#if PJ_IOQUEUE_HAS_SAFE_UNREG
            increment_counter(h);
#endif
            event[event_cnt].key = h;
            event[event_cnt].event_type = READABLE_EVENT;
            ++event_cnt;
        }

#if PJ_HAS_TCP
        if (key_has_pending_connect(h) && PJ_FD_ISSET(h->fd, &xfdset) &&
            !IS_CLOSING(h) && event_cnt < MAX_EVENTS)
        {
#if PJ_IOQUEUE_HAS_SAFE_UNREG
            increment_counter(h);
#endif
            event[event_cnt].key = h;
            event[event_cnt].event_type = EXCEPTION_EVENT;
            ++event_cnt;
        }
#endif
    }

    for (i=0; i<event_cnt; ++i) {
        if (event[i].key->grp_lock)
            pj_grp_lock_add_ref_dbg(event[i].key->grp_lock, "ioqueue", 0);
    }

    PJ_RACE_ME(5);

    pj_lock_release(ioqueue->lock);

    PJ_RACE_ME(5);

    processed_cnt = 0;

    /* Now process all events. The dispatch functions will take care
     * of locking in each of the key
     */
    for (i=0; i<event_cnt; ++i) {

        /* Just do not exceed PJ_IOQUEUE_MAX_EVENTS_IN_SINGLE_POLL */
        if (processed_cnt < PJ_IOQUEUE_MAX_EVENTS_IN_SINGLE_POLL) {
            switch (event[i].event_type) {
            case READABLE_EVENT:
                if (ioqueue_dispatch_read_event(ioqueue, event[i].key))
                    ++processed_cnt;
                break;
            case WRITEABLE_EVENT:
                if (ioqueue_dispatch_write_event(ioqueue, event[i].key))
                    ++processed_cnt;
                break;
            case EXCEPTION_EVENT:
                if (ioqueue_dispatch_exception_event(ioqueue, event[i].key))
                    ++processed_cnt;
                break;
            case NO_EVENT:
                pj_assert(!"Invalid event!");
                break;
            }
        }

#if PJ_IOQUEUE_HAS_SAFE_UNREG
        decrement_counter(event[i].key);
#endif

        if (event[i].key->grp_lock)
            pj_grp_lock_dec_ref_dbg(event[i].key->grp_lock,
                                    "ioqueue", 0);
    }

    TRACE__((THIS_FILE, "     poll: count=%d events=%d processed=%d",
             count, event_cnt, processed_cnt));

    return processed_cnt;
}

