--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/nspr/pr/src/io/prmwait.c	Mon Jul 28 10:47:06 2014 +0200
@@ -0,0 +1,1456 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "primpl.h"
+#include "pprmwait.h"
+
+#define _MW_REHASH_MAX 11
+
+static PRLock *mw_lock = NULL;
+static _PRGlobalState *mw_state = NULL;
+
+static PRIntervalTime max_polling_interval;
+
+#ifdef WINNT
+
+typedef struct TimerEvent {
+    PRIntervalTime absolute;
+    void (*func)(void *);
+    void *arg;
+    LONG ref_count;
+    PRCList links;
+} TimerEvent;
+
+#define TIMER_EVENT_PTR(_qp) \
+    ((TimerEvent *) ((char *) (_qp) - offsetof(TimerEvent, links)))
+
+struct {
+    PRLock *ml;
+    PRCondVar *new_timer;
+    PRCondVar *cancel_timer;
+    PRThread *manager_thread;
+    PRCList timer_queue;
+} tm_vars;
+
+static PRStatus TimerInit(void);
+static void TimerManager(void *arg);
+static TimerEvent *CreateTimer(PRIntervalTime timeout,
+    void (*func)(void *), void *arg);
+static PRBool CancelTimer(TimerEvent *timer);
+
+static void TimerManager(void *arg)
+{
+    PRIntervalTime now;
+    PRIntervalTime timeout;
+    PRCList *head;
+    TimerEvent *timer;
+
+    PR_Lock(tm_vars.ml);
+    while (1)
+    {
+        if (PR_CLIST_IS_EMPTY(&tm_vars.timer_queue))
+        {
+            PR_WaitCondVar(tm_vars.new_timer, PR_INTERVAL_NO_TIMEOUT);
+        }
+        else
+        {
+            now = PR_IntervalNow();
+            head = PR_LIST_HEAD(&tm_vars.timer_queue);
+            timer = TIMER_EVENT_PTR(head);
+            if ((PRInt32) (now - timer->absolute) >= 0)
+            {
+                PR_REMOVE_LINK(head);
+                /*
+                 * make its prev and next point to itself so that
+                 * it's obvious that it's not on the timer_queue.
+                 */
+                PR_INIT_CLIST(head);
+                PR_ASSERT(2 == timer->ref_count);
+                PR_Unlock(tm_vars.ml);
+                timer->func(timer->arg);
+                PR_Lock(tm_vars.ml);
+                timer->ref_count -= 1;
+                if (0 == timer->ref_count)
+                {
+                    PR_NotifyAllCondVar(tm_vars.cancel_timer);
+                }
+            }
+            else
+            {
+                timeout = (PRIntervalTime)(timer->absolute - now);
+                PR_WaitCondVar(tm_vars.new_timer, timeout);
+            } 
+        }
+    }
+    PR_Unlock(tm_vars.ml);
+}
+
+static TimerEvent *CreateTimer(
+    PRIntervalTime timeout,
+    void (*func)(void *),
+    void *arg)
+{
+    TimerEvent *timer;
+    PRCList *links, *tail;
+    TimerEvent *elem;
+
+    timer = PR_NEW(TimerEvent);
+    if (NULL == timer)
+    {
+        PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+        return timer;
+    }
+    timer->absolute = PR_IntervalNow() + timeout;
+    timer->func = func;
+    timer->arg = arg;
+    timer->ref_count = 2;
+    PR_Lock(tm_vars.ml);
+    tail = links = PR_LIST_TAIL(&tm_vars.timer_queue);
+    while (links->prev != tail)
+    {
+        elem = TIMER_EVENT_PTR(links);
+        if ((PRInt32)(timer->absolute - elem->absolute) >= 0)
+        {
+            break;
+        }
+        links = links->prev;
+    }
+    PR_INSERT_AFTER(&timer->links, links);
+    PR_NotifyCondVar(tm_vars.new_timer);
+    PR_Unlock(tm_vars.ml);
+    return timer;
+}
+
+static PRBool CancelTimer(TimerEvent *timer)
+{
+    PRBool canceled = PR_FALSE;
+
+    PR_Lock(tm_vars.ml);
+    timer->ref_count -= 1;
+    if (timer->links.prev == &timer->links)
+    {
+        while (timer->ref_count == 1)
+        {
+            PR_WaitCondVar(tm_vars.cancel_timer, PR_INTERVAL_NO_TIMEOUT);
+        }
+    }
+    else
+    {
+        PR_REMOVE_LINK(&timer->links);
+        canceled = PR_TRUE;
+    }
+    PR_Unlock(tm_vars.ml);
+    PR_DELETE(timer);
+    return canceled; 
+}
+
+static PRStatus TimerInit(void)
+{
+    tm_vars.ml = PR_NewLock();
+    if (NULL == tm_vars.ml)
+    {
+        goto failed;
+    }
+    tm_vars.new_timer = PR_NewCondVar(tm_vars.ml);
+    if (NULL == tm_vars.new_timer)
+    {
+        goto failed;
+    }
+    tm_vars.cancel_timer = PR_NewCondVar(tm_vars.ml);
+    if (NULL == tm_vars.cancel_timer)
+    {
+        goto failed;
+    }
+    PR_INIT_CLIST(&tm_vars.timer_queue);
+    tm_vars.manager_thread = PR_CreateThread(
+        PR_SYSTEM_THREAD, TimerManager, NULL, PR_PRIORITY_NORMAL,
+        PR_LOCAL_THREAD, PR_UNJOINABLE_THREAD, 0);
+    if (NULL == tm_vars.manager_thread)
+    {
+        goto failed;
+    }
+    return PR_SUCCESS;
+
+failed:
+    if (NULL != tm_vars.cancel_timer)
+    {
+        PR_DestroyCondVar(tm_vars.cancel_timer);
+    }
+    if (NULL != tm_vars.new_timer)
+    {
+        PR_DestroyCondVar(tm_vars.new_timer);
+    }
+    if (NULL != tm_vars.ml)
+    {
+        PR_DestroyLock(tm_vars.ml);
+    }
+    return PR_FAILURE;
+}
+
+#endif /* WINNT */
+
+/******************************************************************/
+/******************************************************************/
+/************************ The private portion *********************/
+/******************************************************************/
+/******************************************************************/
+void _PR_InitMW(void)
+{
+#ifdef WINNT
+    /*
+     * We use NT 4's InterlockedCompareExchange() to operate
+     * on PRMWStatus variables.
+     */
+    PR_ASSERT(sizeof(LONG) == sizeof(PRMWStatus));
+    TimerInit();
+#endif
+    mw_lock = PR_NewLock();
+    PR_ASSERT(NULL != mw_lock);
+    mw_state = PR_NEWZAP(_PRGlobalState);
+    PR_ASSERT(NULL != mw_state);
+    PR_INIT_CLIST(&mw_state->group_list);
+    max_polling_interval = PR_MillisecondsToInterval(MAX_POLLING_INTERVAL);
+}  /* _PR_InitMW */
+
+void _PR_CleanupMW(void)
+{
+    PR_DestroyLock(mw_lock);
+    mw_lock = NULL;
+    if (mw_state->group) {
+        PR_DestroyWaitGroup(mw_state->group);
+        /* mw_state->group is set to NULL as a side effect. */
+    }
+    PR_DELETE(mw_state);
+}  /* _PR_CleanupMW */
+
+static PRWaitGroup *MW_Init2(void)
+{
+    PRWaitGroup *group = mw_state->group;  /* it's the null group */
+    if (NULL == group)  /* there is this special case */
+    {
+        group = PR_CreateWaitGroup(_PR_DEFAULT_HASH_LENGTH);
+        if (NULL == group) goto failed_alloc;
+        PR_Lock(mw_lock);
+        if (NULL == mw_state->group)
+        {
+            mw_state->group = group;
+            group = NULL;
+        }
+        PR_Unlock(mw_lock);
+        if (group != NULL) (void)PR_DestroyWaitGroup(group);
+        group = mw_state->group;  /* somebody beat us to it */
+    }
+failed_alloc:
+    return group;  /* whatever */
+}  /* MW_Init2 */
+
+static _PR_HashStory MW_AddHashInternal(PRRecvWait *desc, _PRWaiterHash *hash)
+{
+    /*
+    ** The entries are put in the table using the fd (PRFileDesc*) of
+    ** the receive descriptor as the key. This allows us to locate
+    ** the appropriate entry aqain when the poll operation finishes.
+    **
+    ** The pointer to the file descriptor object is first divided by
+    ** the natural alignment of a pointer in the belief that object
+    ** will have at least that many zeros in the low order bits.
+    ** This may not be a good assuption.
+    **
+    ** We try to put the entry in by rehashing _MW_REHASH_MAX times. After
+    ** that we declare defeat and force the table to be reconstructed.
+    ** Since some fds might be added more than once, won't that cause
+    ** collisions even in an empty table?
+    */
+    PRIntn rehash = _MW_REHASH_MAX;
+    PRRecvWait **waiter;
+    PRUintn hidx = _MW_HASH(desc->fd, hash->length);
+    PRUintn hoffset = 0;
+
+    while (rehash-- > 0)
+    {
+        waiter = &hash->recv_wait;
+        if (NULL == waiter[hidx])
+        {
+            waiter[hidx] = desc;
+            hash->count += 1;
+#if 0
+            printf("Adding 0x%x->0x%x ", desc, desc->fd);
+            printf(
+                "table[%u:%u:*%u]: 0x%x->0x%x\n",
+                hidx, hash->count, hash->length, waiter[hidx], waiter[hidx]->fd);
+#endif
+            return _prmw_success;
+        }
+        if (desc == waiter[hidx])
+        {
+            PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);  /* desc already in table */
+            return _prmw_error;
+        }
+#if 0
+        printf("Failing 0x%x->0x%x ", desc, desc->fd);
+        printf(
+            "table[*%u:%u:%u]: 0x%x->0x%x\n",
+            hidx, hash->count, hash->length, waiter[hidx], waiter[hidx]->fd);
+#endif
+        if (0 == hoffset)
+        {
+            hoffset = _MW_HASH2(desc->fd, hash->length);
+            PR_ASSERT(0 != hoffset);
+        }
+        hidx = (hidx + hoffset) % (hash->length);
+    }
+    return _prmw_rehash;    
+}  /* MW_AddHashInternal */
+
+static _PR_HashStory MW_ExpandHashInternal(PRWaitGroup *group)
+{
+    PRRecvWait **desc;
+    PRUint32 pidx, length;
+    _PRWaiterHash *newHash, *oldHash = group->waiter;
+    PRBool retry;
+    _PR_HashStory hrv;
+
+    static const PRInt32 prime_number[] = {
+        _PR_DEFAULT_HASH_LENGTH, 179, 521, 907, 1427,
+        2711, 3917, 5021, 8219, 11549, 18911, 26711, 33749, 44771};
+    PRUintn primes = (sizeof(prime_number) / sizeof(PRInt32));
+
+    /* look up the next size we'd like to use for the hash table */
+    for (pidx = 0; pidx < primes; ++pidx)
+    {
+        if (prime_number[pidx] == oldHash->length)
+        {
+            break;
+        }
+    }
+    /* table size must be one of the prime numbers */
+    PR_ASSERT(pidx < primes);
+
+    /* if pidx == primes - 1, we can't expand the table any more */
+    while (pidx < primes - 1)
+    {
+        /* next size */
+        ++pidx;
+        length = prime_number[pidx];
+
+        /* allocate the new hash table and fill it in with the old */
+        newHash = (_PRWaiterHash*)PR_CALLOC(
+            sizeof(_PRWaiterHash) + (length * sizeof(PRRecvWait*)));
+        if (NULL == newHash)
+        {
+            PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+            return _prmw_error;
+        }
+
+        newHash->length = length;
+        retry = PR_FALSE;
+        for (desc = &oldHash->recv_wait;
+            newHash->count < oldHash->count; ++desc)
+        {
+            PR_ASSERT(desc < &oldHash->recv_wait + oldHash->length);
+            if (NULL != *desc)
+            {
+                hrv = MW_AddHashInternal(*desc, newHash);
+                PR_ASSERT(_prmw_error != hrv);
+                if (_prmw_success != hrv)
+                {
+                    PR_DELETE(newHash);
+                    retry = PR_TRUE;
+                    break;
+                }
+            }
+        }
+        if (retry) continue;
+
+        PR_DELETE(group->waiter);
+        group->waiter = newHash;
+        group->p_timestamp += 1;
+        return _prmw_success;
+    }
+
+    PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+    return _prmw_error;  /* we're hosed */
+}  /* MW_ExpandHashInternal */
+
+#ifndef WINNT
+static void _MW_DoneInternal(
+    PRWaitGroup *group, PRRecvWait **waiter, PRMWStatus outcome)
+{
+    /*
+    ** Add this receive wait object to the list of finished I/O
+    ** operations for this particular group. If there are other
+    ** threads waiting on the group, notify one. If not, arrange
+    ** for this thread to return.
+    */
+
+#if 0
+    printf("Removing 0x%x->0x%x\n", *waiter, (*waiter)->fd);
+#endif
+    (*waiter)->outcome = outcome;
+    PR_APPEND_LINK(&((*waiter)->internal), &group->io_ready);
+    PR_NotifyCondVar(group->io_complete);
+    PR_ASSERT(0 != group->waiter->count);
+    group->waiter->count -= 1;
+    *waiter = NULL;
+}  /* _MW_DoneInternal */
+#endif /* WINNT */
+
+static PRRecvWait **_MW_LookupInternal(PRWaitGroup *group, PRFileDesc *fd)
+{
+    /*
+    ** Find the receive wait object corresponding to the file descriptor.
+    ** Only search the wait group specified.
+    */
+    PRRecvWait **desc;
+    PRIntn rehash = _MW_REHASH_MAX;
+    _PRWaiterHash *hash = group->waiter;
+    PRUintn hidx = _MW_HASH(fd, hash->length);
+    PRUintn hoffset = 0;
+    
+    while (rehash-- > 0)
+    {
+        desc = (&hash->recv_wait) + hidx;
+        if ((*desc != NULL) && ((*desc)->fd == fd)) return desc;
+        if (0 == hoffset)
+        {
+            hoffset = _MW_HASH2(fd, hash->length);
+            PR_ASSERT(0 != hoffset);
+        }
+        hidx = (hidx + hoffset) % (hash->length);
+    }
+    return NULL;
+}  /* _MW_LookupInternal */
+
+#ifndef WINNT
+static PRStatus _MW_PollInternal(PRWaitGroup *group)
+{
+    PRRecvWait **waiter;
+    PRStatus rv = PR_FAILURE;
+    PRInt32 count, count_ready;
+    PRIntervalTime polling_interval;
+
+    group->poller = PR_GetCurrentThread();
+
+    while (PR_TRUE)
+    {
+        PRIntervalTime now, since_last_poll;
+        PRPollDesc *poll_list;
+
+        while (0 == group->waiter->count)
+        {
+            PRStatus st;
+            st = PR_WaitCondVar(group->new_business, PR_INTERVAL_NO_TIMEOUT);
+            if (_prmw_running != group->state)
+            {
+                PR_SetError(PR_INVALID_STATE_ERROR, 0);
+                goto aborted;
+            }
+            if (_MW_ABORTED(st)) goto aborted;
+        }
+
+        /*
+        ** There's something to do. See if our existing polling list
+        ** is large enough for what we have to do?
+        */
+
+        while (group->polling_count < group->waiter->count)
+        {
+            PRUint32 old_count = group->waiter->count;
+            PRUint32 new_count = PR_ROUNDUP(old_count, _PR_POLL_COUNT_FUDGE);
+            PRSize new_size = sizeof(PRPollDesc) * new_count;
+            PRPollDesc *old_polling_list = group->polling_list;
+
+            PR_Unlock(group->ml);
+            poll_list = (PRPollDesc*)PR_CALLOC(new_size);
+            if (NULL == poll_list)
+            {
+                PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+                PR_Lock(group->ml);
+                goto failed_alloc;
+            }
+            if (NULL != old_polling_list)
+                PR_DELETE(old_polling_list);
+            PR_Lock(group->ml);
+            if (_prmw_running != group->state)
+            {
+                PR_SetError(PR_INVALID_STATE_ERROR, 0);
+                goto aborted;
+            }
+            group->polling_list = poll_list;
+            group->polling_count = new_count;
+        }
+
+        now = PR_IntervalNow();
+        polling_interval = max_polling_interval;
+        since_last_poll = now - group->last_poll;
+
+        waiter = &group->waiter->recv_wait;
+        poll_list = group->polling_list;
+        for (count = 0; count < group->waiter->count; ++waiter)
+        {
+            PR_ASSERT(waiter < &group->waiter->recv_wait
+                + group->waiter->length);
+            if (NULL != *waiter)  /* a live one! */
+            {
+                if ((PR_INTERVAL_NO_TIMEOUT != (*waiter)->timeout)
+                && (since_last_poll >= (*waiter)->timeout))
+                    _MW_DoneInternal(group, waiter, PR_MW_TIMEOUT);
+                else
+                {
+                    if (PR_INTERVAL_NO_TIMEOUT != (*waiter)->timeout)
+                    {
+                        (*waiter)->timeout -= since_last_poll;
+                        if ((*waiter)->timeout < polling_interval)
+                            polling_interval = (*waiter)->timeout;
+                    }
+                    PR_ASSERT(poll_list < group->polling_list
+                        + group->polling_count);
+                    poll_list->fd = (*waiter)->fd;
+                    poll_list->in_flags = PR_POLL_READ;
+                    poll_list->out_flags = 0;
+#if 0
+                    printf(
+                        "Polling 0x%x[%d]: [fd: 0x%x, tmo: %u]\n",
+                        poll_list, count, poll_list->fd, (*waiter)->timeout);
+#endif
+                    poll_list += 1;
+                    count += 1;
+                }
+            }
+        } 
+
+        PR_ASSERT(count == group->waiter->count);
+
+        /*
+        ** If there are no more threads waiting for completion,
+        ** we need to return.
+        */
+        if ((!PR_CLIST_IS_EMPTY(&group->io_ready))
+        && (1 == group->waiting_threads)) break;
+
+        if (0 == count) continue;  /* wait for new business */
+
+        group->last_poll = now;
+
+        PR_Unlock(group->ml);
+
+        count_ready = PR_Poll(group->polling_list, count, polling_interval);
+
+        PR_Lock(group->ml);
+
+        if (_prmw_running != group->state)
+        {
+            PR_SetError(PR_INVALID_STATE_ERROR, 0);
+            goto aborted;
+        }
+        if (-1 == count_ready)
+        {
+            goto failed_poll;  /* that's a shame */
+        }
+        else if (0 < count_ready)
+        {
+            for (poll_list = group->polling_list; count > 0;
+            poll_list++, count--)
+            {
+                PR_ASSERT(
+                    poll_list < group->polling_list + group->polling_count);
+                if (poll_list->out_flags != 0)
+                {
+                    waiter = _MW_LookupInternal(group, poll_list->fd);
+                    /*
+                    ** If 'waiter' is NULL, that means the wait receive
+                    ** descriptor has been canceled.
+                    */
+                    if (NULL != waiter)
+                        _MW_DoneInternal(group, waiter, PR_MW_SUCCESS);
+                }
+            }
+        }
+        /*
+        ** If there are no more threads waiting for completion,
+        ** we need to return.
+        ** This thread was "borrowed" to do the polling, but it really
+        ** belongs to the client.
+        */
+        if ((!PR_CLIST_IS_EMPTY(&group->io_ready))
+        && (1 == group->waiting_threads)) break;
+    }
+
+    rv = PR_SUCCESS;
+
+aborted:
+failed_poll:
+failed_alloc:
+    group->poller = NULL;  /* we were that, not we ain't */
+    if ((_prmw_running == group->state) && (group->waiting_threads > 1))
+    {
+        /* Wake up one thread to become the new poller. */
+        PR_NotifyCondVar(group->io_complete);
+    }
+    return rv;  /* we return with the lock held */
+}  /* _MW_PollInternal */
+#endif /* !WINNT */
+
+static PRMWGroupState MW_TestForShutdownInternal(PRWaitGroup *group)
+{
+    PRMWGroupState rv = group->state;
+    /*
+    ** Looking at the group's fields is safe because
+    ** once the group's state is no longer running, it
+    ** cannot revert and there is a safe check on entry
+    ** to make sure no more threads are made to wait.
+    */
+    if ((_prmw_stopping == rv)
+    && (0 == group->waiting_threads))
+    {
+        rv = group->state = _prmw_stopped;
+        PR_NotifyCondVar(group->mw_manage);
+    }
+    return rv;
+}  /* MW_TestForShutdownInternal */
+
+#ifndef WINNT
+static void _MW_InitialRecv(PRCList *io_ready)
+{
+    PRRecvWait *desc = (PRRecvWait*)io_ready;
+    if ((NULL == desc->buffer.start)
+    || (0 == desc->buffer.length))
+        desc->bytesRecv = 0;
+    else
+    {
+        desc->bytesRecv = (desc->fd->methods->recv)(
+            desc->fd, desc->buffer.start,
+            desc->buffer.length, 0, desc->timeout);
+        if (desc->bytesRecv < 0)  /* SetError should already be there */
+            desc->outcome = PR_MW_FAILURE;
+    }
+}  /* _MW_InitialRecv */
+#endif
+
+#ifdef WINNT
+static void NT_TimeProc(void *arg)
+{
+    _MDOverlapped *overlapped = (_MDOverlapped *)arg;
+    PRRecvWait *desc =  overlapped->data.mw.desc;
+    PRFileDesc *bottom;
+    
+    if (InterlockedCompareExchange((LONG *)&desc->outcome,
+        (LONG)PR_MW_TIMEOUT, (LONG)PR_MW_PENDING) != (LONG)PR_MW_PENDING)
+    {
+        /* This wait recv descriptor has already completed. */
+        return;
+    }
+
+    /* close the osfd to abort the outstanding async io request */
+    /* $$$$
+    ** Little late to be checking if NSPR's on the bottom of stack,
+    ** but if we don't check, we can't assert that the private data
+    ** is what we think it is.
+    ** $$$$
+    */
+    bottom = PR_GetIdentitiesLayer(desc->fd, PR_NSPR_IO_LAYER);
+    PR_ASSERT(NULL != bottom);
+    if (NULL != bottom)  /* now what!?!?! */
+    {
+        bottom->secret->state = _PR_FILEDESC_CLOSED;
+        if (closesocket(bottom->secret->md.osfd) == SOCKET_ERROR)
+        {
+            fprintf(stderr, "closesocket failed: %d\n", WSAGetLastError());
+            PR_ASSERT(!"What shall I do?");
+        }
+    }
+    return;
+}  /* NT_TimeProc */
+
+static PRStatus NT_HashRemove(PRWaitGroup *group, PRFileDesc *fd)
+{
+    PRRecvWait **waiter;
+
+    _PR_MD_LOCK(&group->mdlock);
+    waiter = _MW_LookupInternal(group, fd);
+    if (NULL != waiter)
+    {
+        group->waiter->count -= 1;
+        *waiter = NULL;
+    }
+    _PR_MD_UNLOCK(&group->mdlock);
+    return (NULL != waiter) ? PR_SUCCESS : PR_FAILURE;
+}
+
+PRStatus NT_HashRemoveInternal(PRWaitGroup *group, PRFileDesc *fd)
+{
+    PRRecvWait **waiter;
+
+    waiter = _MW_LookupInternal(group, fd);
+    if (NULL != waiter)
+    {
+        group->waiter->count -= 1;
+        *waiter = NULL;
+    }
+    return (NULL != waiter) ? PR_SUCCESS : PR_FAILURE;
+}
+#endif /* WINNT */
+
+/******************************************************************/
+/******************************************************************/
+/********************** The public API portion ********************/
+/******************************************************************/
+/******************************************************************/
+PR_IMPLEMENT(PRStatus) PR_AddWaitFileDesc(
+    PRWaitGroup *group, PRRecvWait *desc)
+{
+    _PR_HashStory hrv;
+    PRStatus rv = PR_FAILURE;
+#ifdef WINNT
+    _MDOverlapped *overlapped;
+    HANDLE hFile;
+    BOOL bResult;
+    DWORD dwError;
+    PRFileDesc *bottom;
+#endif
+
+    if (!_pr_initialized) _PR_ImplicitInitialization();
+    if ((NULL == group) && (NULL == (group = MW_Init2())))
+    {
+        return rv;
+    }
+
+    PR_ASSERT(NULL != desc->fd);
+
+    desc->outcome = PR_MW_PENDING;  /* nice, well known value */
+    desc->bytesRecv = 0;  /* likewise, though this value is ambiguious */
+
+    PR_Lock(group->ml);
+
+    if (_prmw_running != group->state)
+    {
+        /* Not allowed to add after cancelling the group */
+        desc->outcome = PR_MW_INTERRUPT;
+        PR_SetError(PR_INVALID_STATE_ERROR, 0);
+        PR_Unlock(group->ml);
+        return rv;
+    }
+
+#ifdef WINNT
+    _PR_MD_LOCK(&group->mdlock);
+#endif
+
+    /*
+    ** If the waiter count is zero at this point, there's no telling
+    ** how long we've been idle. Therefore, initialize the beginning
+    ** of the timing interval. As long as the list doesn't go empty,
+    ** it will maintain itself.
+    */
+    if (0 == group->waiter->count)
+        group->last_poll = PR_IntervalNow();
+
+    do
+    {
+        hrv = MW_AddHashInternal(desc, group->waiter);
+        if (_prmw_rehash != hrv) break;
+        hrv = MW_ExpandHashInternal(group);  /* gruesome */
+        if (_prmw_success != hrv) break;
+    } while (PR_TRUE);
+
+#ifdef WINNT
+    _PR_MD_UNLOCK(&group->mdlock);
+#endif
+
+    PR_NotifyCondVar(group->new_business);  /* tell the world */
+    rv = (_prmw_success == hrv) ? PR_SUCCESS : PR_FAILURE;
+    PR_Unlock(group->ml);
+
+#ifdef WINNT
+    overlapped = PR_NEWZAP(_MDOverlapped);
+    if (NULL == overlapped)
+    {
+        PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+        NT_HashRemove(group, desc->fd);
+        return rv;
+    }
+    overlapped->ioModel = _MD_MultiWaitIO;
+    overlapped->data.mw.desc = desc;
+    overlapped->data.mw.group = group;
+    if (desc->timeout != PR_INTERVAL_NO_TIMEOUT)
+    {
+        overlapped->data.mw.timer = CreateTimer(
+            desc->timeout,
+            NT_TimeProc,
+            overlapped);
+        if (0 == overlapped->data.mw.timer)
+        {
+            NT_HashRemove(group, desc->fd);
+            PR_DELETE(overlapped);
+            /*
+             * XXX It appears that a maximum of 16 timer events can
+             * be outstanding. GetLastError() returns 0 when I try it.
+             */
+            PR_SetError(PR_INSUFFICIENT_RESOURCES_ERROR, GetLastError());
+            return PR_FAILURE;
+        }
+    }
+
+    /* Reach to the bottom layer to get the OS fd */
+    bottom = PR_GetIdentitiesLayer(desc->fd, PR_NSPR_IO_LAYER);
+    PR_ASSERT(NULL != bottom);
+    if (NULL == bottom)
+    {
+        PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+        return PR_FAILURE;
+    }
+    hFile = (HANDLE)bottom->secret->md.osfd; 
+    if (!bottom->secret->md.io_model_committed)
+    {
+        PRInt32 st;
+        st = _md_Associate(hFile);
+        PR_ASSERT(0 != st);
+        bottom->secret->md.io_model_committed = PR_TRUE;
+    }
+    bResult = ReadFile(hFile,
+        desc->buffer.start,
+        (DWORD)desc->buffer.length,
+        NULL,
+        &overlapped->overlapped);
+    if (FALSE == bResult && (dwError = GetLastError()) != ERROR_IO_PENDING)
+    {
+        if (desc->timeout != PR_INTERVAL_NO_TIMEOUT)
+        {
+            if (InterlockedCompareExchange((LONG *)&desc->outcome,
+                (LONG)PR_MW_FAILURE, (LONG)PR_MW_PENDING)
+                == (LONG)PR_MW_PENDING)
+            {
+                CancelTimer(overlapped->data.mw.timer);
+            }
+            NT_HashRemove(group, desc->fd);
+            PR_DELETE(overlapped);
+        }
+        _PR_MD_MAP_READ_ERROR(dwError);
+        rv = PR_FAILURE;
+    }
+#endif
+
+    return rv;
+}  /* PR_AddWaitFileDesc */
+
+PR_IMPLEMENT(PRRecvWait*) PR_WaitRecvReady(PRWaitGroup *group)
+{
+    PRCList *io_ready = NULL;
+#ifdef WINNT
+    PRThread *me = _PR_MD_CURRENT_THREAD();
+    _MDOverlapped *overlapped;    
+#endif
+
+    if (!_pr_initialized) _PR_ImplicitInitialization();
+    if ((NULL == group) && (NULL == (group = MW_Init2()))) goto failed_init;
+
+    PR_Lock(group->ml);
+
+    if (_prmw_running != group->state)
+    {
+        PR_SetError(PR_INVALID_STATE_ERROR, 0);
+        goto invalid_state;
+    }
+
+    group->waiting_threads += 1;  /* the polling thread is counted */
+
+#ifdef WINNT
+    _PR_MD_LOCK(&group->mdlock);
+    while (PR_CLIST_IS_EMPTY(&group->io_ready))
+    {
+        _PR_THREAD_LOCK(me);
+        me->state = _PR_IO_WAIT;
+        PR_APPEND_LINK(&me->waitQLinks, &group->wait_list);
+        if (!_PR_IS_NATIVE_THREAD(me))
+        {
+            _PR_SLEEPQ_LOCK(me->cpu);
+            _PR_ADD_SLEEPQ(me, PR_INTERVAL_NO_TIMEOUT);
+            _PR_SLEEPQ_UNLOCK(me->cpu);
+        }
+        _PR_THREAD_UNLOCK(me);
+        _PR_MD_UNLOCK(&group->mdlock);
+        PR_Unlock(group->ml);
+        _PR_MD_WAIT(me, PR_INTERVAL_NO_TIMEOUT);
+        me->state = _PR_RUNNING;
+        PR_Lock(group->ml);
+        _PR_MD_LOCK(&group->mdlock);
+        if (_PR_PENDING_INTERRUPT(me)) {
+            PR_REMOVE_LINK(&me->waitQLinks);
+            _PR_MD_UNLOCK(&group->mdlock);
+            me->flags &= ~_PR_INTERRUPT;
+            me->io_suspended = PR_FALSE;
+            PR_SetError(PR_PENDING_INTERRUPT_ERROR, 0);
+            goto aborted;
+        }
+    }
+    io_ready = PR_LIST_HEAD(&group->io_ready);
+    PR_ASSERT(io_ready != NULL);
+    PR_REMOVE_LINK(io_ready);
+    _PR_MD_UNLOCK(&group->mdlock);
+    overlapped = (_MDOverlapped *)
+        ((char *)io_ready - offsetof(_MDOverlapped, data));
+    io_ready = &overlapped->data.mw.desc->internal;
+#else
+    do
+    {
+        /*
+        ** If the I/O ready list isn't empty, have this thread
+        ** return with the first receive wait object that's available.
+        */
+        if (PR_CLIST_IS_EMPTY(&group->io_ready))
+        {
+            /*
+            ** Is there a polling thread yet? If not, grab this thread
+            ** and use it.
+            */
+            if (NULL == group->poller)
+            {
+                /*
+                ** This thread will stay do polling until it becomes the only one
+                ** left to service a completion. Then it will return and there will
+                ** be none left to actually poll or to run completions.
+                **
+                ** The polling function should only return w/ failure or
+                ** with some I/O ready.
+                */
+                if (PR_FAILURE == _MW_PollInternal(group)) goto failed_poll;
+            }
+            else
+            {
+                /*
+                ** There are four reasons a thread can be awakened from
+                ** a wait on the io_complete condition variable.
+                ** 1. Some I/O has completed, i.e., the io_ready list
+                **    is nonempty.
+                ** 2. The wait group is canceled.
+                ** 3. The thread is interrupted.
+                ** 4. The current polling thread has to leave and needs
+                **    a replacement.
+                ** The logic to find a new polling thread is made more
+                ** complicated by all the other possible events.
+                ** I tried my best to write the logic clearly, but
+                ** it is still full of if's with continue and goto.
+                */
+                PRStatus st;
+                do 
+                {
+                    st = PR_WaitCondVar(group->io_complete, PR_INTERVAL_NO_TIMEOUT);
+                    if (_prmw_running != group->state)
+                    {
+                        PR_SetError(PR_INVALID_STATE_ERROR, 0);
+                        goto aborted;
+                    }
+                    if (_MW_ABORTED(st) || (NULL == group->poller)) break;
+                } while (PR_CLIST_IS_EMPTY(&group->io_ready));
+
+                /*
+                ** The thread is interrupted and has to leave.  It might
+                ** have also been awakened to process ready i/o or be the
+                ** new poller.  To be safe, if either condition is true,
+                ** we awaken another thread to take its place.
+                */
+                if (_MW_ABORTED(st))
+                {
+                    if ((NULL == group->poller
+                    || !PR_CLIST_IS_EMPTY(&group->io_ready))
+                    && group->waiting_threads > 1)
+                        PR_NotifyCondVar(group->io_complete);
+                    goto aborted;
+                }
+
+                /*
+                ** A new poller is needed, but can I be the new poller?
+                ** If there is no i/o ready, sure.  But if there is any
+                ** i/o ready, it has a higher priority.  I want to
+                ** process the ready i/o first and wake up another
+                ** thread to be the new poller.
+                */ 
+                if (NULL == group->poller)
+                {
+                    if (PR_CLIST_IS_EMPTY(&group->io_ready))
+                        continue;
+                    if (group->waiting_threads > 1)
+                        PR_NotifyCondVar(group->io_complete);
+                }
+            }
+            PR_ASSERT(!PR_CLIST_IS_EMPTY(&group->io_ready));
+        }
+        io_ready = PR_LIST_HEAD(&group->io_ready);
+        PR_NotifyCondVar(group->io_taken);
+        PR_ASSERT(io_ready != NULL);
+        PR_REMOVE_LINK(io_ready);
+    } while (NULL == io_ready);
+
+failed_poll:
+
+#endif
+
+aborted:
+
+    group->waiting_threads -= 1;
+invalid_state:
+    (void)MW_TestForShutdownInternal(group);
+    PR_Unlock(group->ml);
+
+failed_init:
+    if (NULL != io_ready)
+    {
+        /* If the operation failed, record the reason why */
+        switch (((PRRecvWait*)io_ready)->outcome)
+        {
+            case PR_MW_PENDING:
+                PR_ASSERT(0);
+                break;
+            case PR_MW_SUCCESS:
+#ifndef WINNT
+                _MW_InitialRecv(io_ready);
+#endif
+                break;
+#ifdef WINNT
+            case PR_MW_FAILURE:
+                _PR_MD_MAP_READ_ERROR(overlapped->data.mw.error);
+                break;
+#endif
+            case PR_MW_TIMEOUT:
+                PR_SetError(PR_IO_TIMEOUT_ERROR, 0);
+                break;
+            case PR_MW_INTERRUPT:
+                PR_SetError(PR_PENDING_INTERRUPT_ERROR, 0);
+                break;
+            default: break;
+        }
+#ifdef WINNT
+        if (NULL != overlapped->data.mw.timer)
+        {
+            PR_ASSERT(PR_INTERVAL_NO_TIMEOUT
+                != overlapped->data.mw.desc->timeout);
+            CancelTimer(overlapped->data.mw.timer);
+        }
+        else
+        {
+            PR_ASSERT(PR_INTERVAL_NO_TIMEOUT
+                == overlapped->data.mw.desc->timeout);
+        }
+        PR_DELETE(overlapped);
+#endif
+    }
+    return (PRRecvWait*)io_ready;
+}  /* PR_WaitRecvReady */
+
+PR_IMPLEMENT(PRStatus) PR_CancelWaitFileDesc(PRWaitGroup *group, PRRecvWait *desc)
+{
+#if !defined(WINNT)
+    PRRecvWait **recv_wait;
+#endif
+    PRStatus rv = PR_SUCCESS;
+    if (NULL == group) group = mw_state->group;
+    PR_ASSERT(NULL != group);
+    if (NULL == group)
+    {
+        PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+        return PR_FAILURE;
+    }
+
+    PR_Lock(group->ml);
+
+    if (_prmw_running != group->state)
+    {
+        PR_SetError(PR_INVALID_STATE_ERROR, 0);
+        rv = PR_FAILURE;
+        goto unlock;
+    }
+
+#ifdef WINNT
+    if (InterlockedCompareExchange((LONG *)&desc->outcome,
+        (LONG)PR_MW_INTERRUPT, (LONG)PR_MW_PENDING) == (LONG)PR_MW_PENDING)
+    {
+        PRFileDesc *bottom = PR_GetIdentitiesLayer(desc->fd, PR_NSPR_IO_LAYER);
+        PR_ASSERT(NULL != bottom);
+        if (NULL == bottom)
+        {
+            PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+            goto unlock;
+        }
+        bottom->secret->state = _PR_FILEDESC_CLOSED;
+#if 0
+        fprintf(stderr, "cancel wait recv: closing socket\n");
+#endif
+        if (closesocket(bottom->secret->md.osfd) == SOCKET_ERROR)
+        {
+            fprintf(stderr, "closesocket failed: %d\n", WSAGetLastError());
+            exit(1);
+        }
+    }
+#else
+    if (NULL != (recv_wait = _MW_LookupInternal(group, desc->fd)))
+    {
+        /* it was in the wait table */
+        _MW_DoneInternal(group, recv_wait, PR_MW_INTERRUPT);
+        goto unlock;
+    }
+    if (!PR_CLIST_IS_EMPTY(&group->io_ready))
+    {
+        /* is it already complete? */
+        PRCList *head = PR_LIST_HEAD(&group->io_ready);
+        do
+        {
+            PRRecvWait *done = (PRRecvWait*)head;
+            if (done == desc) goto unlock;
+            head = PR_NEXT_LINK(head);
+        } while (head != &group->io_ready);
+    }
+    PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+    rv = PR_FAILURE;
+
+#endif
+unlock:
+    PR_Unlock(group->ml);
+    return rv;
+}  /* PR_CancelWaitFileDesc */
+
+PR_IMPLEMENT(PRRecvWait*) PR_CancelWaitGroup(PRWaitGroup *group)
+{
+    PRRecvWait **desc;
+    PRRecvWait *recv_wait = NULL;
+#ifdef WINNT
+    _MDOverlapped *overlapped;
+    PRRecvWait **end;
+    PRThread *me = _PR_MD_CURRENT_THREAD();
+#endif
+
+    if (NULL == group) group = mw_state->group;
+    PR_ASSERT(NULL != group);
+    if (NULL == group)
+    {
+        PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+        return NULL;
+    }
+
+    PR_Lock(group->ml);
+    if (_prmw_stopped != group->state)
+    {
+        if (_prmw_running == group->state)
+            group->state = _prmw_stopping;  /* so nothing new comes in */
+        if (0 == group->waiting_threads)  /* is there anybody else? */
+            group->state = _prmw_stopped;  /* we can stop right now */
+        else
+        {
+            PR_NotifyAllCondVar(group->new_business);
+            PR_NotifyAllCondVar(group->io_complete);
+        }
+        while (_prmw_stopped != group->state)
+            (void)PR_WaitCondVar(group->mw_manage, PR_INTERVAL_NO_TIMEOUT);
+    }
+
+#ifdef WINNT
+    _PR_MD_LOCK(&group->mdlock);
+#endif
+    /* make all the existing descriptors look done/interrupted */
+#ifdef WINNT
+    end = &group->waiter->recv_wait + group->waiter->length;
+    for (desc = &group->waiter->recv_wait; desc < end; ++desc)
+    {
+        if (NULL != *desc)
+        {
+            if (InterlockedCompareExchange((LONG *)&(*desc)->outcome,
+                (LONG)PR_MW_INTERRUPT, (LONG)PR_MW_PENDING)
+                == (LONG)PR_MW_PENDING)
+            {
+                PRFileDesc *bottom = PR_GetIdentitiesLayer(
+                    (*desc)->fd, PR_NSPR_IO_LAYER);
+                PR_ASSERT(NULL != bottom);
+                if (NULL == bottom)
+                {
+                    PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+                    goto invalid_arg;
+                }
+                bottom->secret->state = _PR_FILEDESC_CLOSED;
+#if 0
+                fprintf(stderr, "cancel wait group: closing socket\n");
+#endif
+                if (closesocket(bottom->secret->md.osfd) == SOCKET_ERROR)
+                {
+                    fprintf(stderr, "closesocket failed: %d\n",
+                        WSAGetLastError());
+                    exit(1);
+                }
+            }
+        }
+    }
+    while (group->waiter->count > 0)
+    {
+        _PR_THREAD_LOCK(me);
+        me->state = _PR_IO_WAIT;
+        PR_APPEND_LINK(&me->waitQLinks, &group->wait_list);
+        if (!_PR_IS_NATIVE_THREAD(me))
+        {
+            _PR_SLEEPQ_LOCK(me->cpu);
+            _PR_ADD_SLEEPQ(me, PR_INTERVAL_NO_TIMEOUT);
+            _PR_SLEEPQ_UNLOCK(me->cpu);
+        }
+        _PR_THREAD_UNLOCK(me);
+        _PR_MD_UNLOCK(&group->mdlock);
+        PR_Unlock(group->ml);
+        _PR_MD_WAIT(me, PR_INTERVAL_NO_TIMEOUT);
+        me->state = _PR_RUNNING;
+        PR_Lock(group->ml);
+        _PR_MD_LOCK(&group->mdlock);
+    }
+#else
+    for (desc = &group->waiter->recv_wait; group->waiter->count > 0; ++desc)
+    {
+        PR_ASSERT(desc < &group->waiter->recv_wait + group->waiter->length);
+        if (NULL != *desc)
+            _MW_DoneInternal(group, desc, PR_MW_INTERRUPT);
+    }
+#endif
+
+    /* take first element of finished list and return it or NULL */
+    if (PR_CLIST_IS_EMPTY(&group->io_ready))
+        PR_SetError(PR_GROUP_EMPTY_ERROR, 0);
+    else
+    {
+        PRCList *head = PR_LIST_HEAD(&group->io_ready);
+        PR_REMOVE_AND_INIT_LINK(head);
+#ifdef WINNT
+        overlapped = (_MDOverlapped *)
+            ((char *)head - offsetof(_MDOverlapped, data));
+        head = &overlapped->data.mw.desc->internal;
+        if (NULL != overlapped->data.mw.timer)
+        {
+            PR_ASSERT(PR_INTERVAL_NO_TIMEOUT
+                != overlapped->data.mw.desc->timeout);
+            CancelTimer(overlapped->data.mw.timer);
+        }
+        else
+        {
+            PR_ASSERT(PR_INTERVAL_NO_TIMEOUT
+                == overlapped->data.mw.desc->timeout);
+        }
+        PR_DELETE(overlapped);
+#endif
+        recv_wait = (PRRecvWait*)head;
+    }
+#ifdef WINNT
+invalid_arg:
+    _PR_MD_UNLOCK(&group->mdlock);
+#endif
+    PR_Unlock(group->ml);
+
+    return recv_wait;
+}  /* PR_CancelWaitGroup */
+
+PR_IMPLEMENT(PRWaitGroup*) PR_CreateWaitGroup(PRInt32 size /* ignored */)
+{
+    PRWaitGroup *wg;
+
+    if (NULL == (wg = PR_NEWZAP(PRWaitGroup)))
+    {
+        PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+        goto failed;
+    }
+    /* the wait group itself */
+    wg->ml = PR_NewLock();
+    if (NULL == wg->ml) goto failed_lock;
+    wg->io_taken = PR_NewCondVar(wg->ml);
+    if (NULL == wg->io_taken) goto failed_cvar0;
+    wg->io_complete = PR_NewCondVar(wg->ml);
+    if (NULL == wg->io_complete) goto failed_cvar1;
+    wg->new_business = PR_NewCondVar(wg->ml);
+    if (NULL == wg->new_business) goto failed_cvar2;
+    wg->mw_manage = PR_NewCondVar(wg->ml);
+    if (NULL == wg->mw_manage) goto failed_cvar3;
+
+    PR_INIT_CLIST(&wg->group_link);
+    PR_INIT_CLIST(&wg->io_ready);
+
+    /* the waiters sequence */
+    wg->waiter = (_PRWaiterHash*)PR_CALLOC(
+        sizeof(_PRWaiterHash) +
+        (_PR_DEFAULT_HASH_LENGTH * sizeof(PRRecvWait*)));
+    if (NULL == wg->waiter)
+    {
+        PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+        goto failed_waiter;
+    }
+    wg->waiter->count = 0;
+    wg->waiter->length = _PR_DEFAULT_HASH_LENGTH;
+
+#ifdef WINNT
+    _PR_MD_NEW_LOCK(&wg->mdlock);
+    PR_INIT_CLIST(&wg->wait_list);
+#endif /* WINNT */
+
+    PR_Lock(mw_lock);
+    PR_APPEND_LINK(&wg->group_link, &mw_state->group_list);
+    PR_Unlock(mw_lock);
+    return wg;
+
+failed_waiter:
+    PR_DestroyCondVar(wg->mw_manage);
+failed_cvar3:
+    PR_DestroyCondVar(wg->new_business);
+failed_cvar2:
+    PR_DestroyCondVar(wg->io_complete);
+failed_cvar1:
+    PR_DestroyCondVar(wg->io_taken);
+failed_cvar0:
+    PR_DestroyLock(wg->ml);
+failed_lock:
+    PR_DELETE(wg);
+    wg = NULL;
+
+failed:
+    return wg;
+}  /* MW_CreateWaitGroup */
+
+PR_IMPLEMENT(PRStatus) PR_DestroyWaitGroup(PRWaitGroup *group)
+{
+    PRStatus rv = PR_SUCCESS;
+    if (NULL == group) group = mw_state->group;
+    PR_ASSERT(NULL != group);
+    if (NULL != group)
+    {
+        PR_Lock(group->ml);
+        if ((group->waiting_threads == 0)
+        && (group->waiter->count == 0)
+        && PR_CLIST_IS_EMPTY(&group->io_ready))
+        {
+            group->state = _prmw_stopped;
+        }
+        else
+        {
+            PR_SetError(PR_INVALID_STATE_ERROR, 0);
+            rv = PR_FAILURE;
+        }
+        PR_Unlock(group->ml);
+        if (PR_FAILURE == rv) return rv;
+
+        PR_Lock(mw_lock);
+        PR_REMOVE_LINK(&group->group_link);
+        PR_Unlock(mw_lock);
+
+#ifdef WINNT
+        /*
+         * XXX make sure wait_list is empty and waiter is empty.
+         * These must be checked while holding mdlock.
+         */
+        _PR_MD_FREE_LOCK(&group->mdlock);
+#endif
+
+        PR_DELETE(group->waiter);
+        PR_DELETE(group->polling_list);
+        PR_DestroyCondVar(group->mw_manage);
+        PR_DestroyCondVar(group->new_business);
+        PR_DestroyCondVar(group->io_complete);
+        PR_DestroyCondVar(group->io_taken);
+        PR_DestroyLock(group->ml);
+        if (group == mw_state->group) mw_state->group = NULL;
+        PR_DELETE(group);
+    }
+    else
+    {
+        /* The default wait group is not created yet. */
+        PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+        rv = PR_FAILURE;
+    }
+    return rv;
+}  /* PR_DestroyWaitGroup */
+
+/**********************************************************************
+***********************************************************************
+******************** Wait group enumerations **************************
+***********************************************************************
+**********************************************************************/
+
+PR_IMPLEMENT(PRMWaitEnumerator*) PR_CreateMWaitEnumerator(PRWaitGroup *group)
+{
+    PRMWaitEnumerator *enumerator = PR_NEWZAP(PRMWaitEnumerator);
+    if (NULL == enumerator) PR_SetError(PR_OUT_OF_MEMORY_ERROR, 0);
+    else
+    {
+        enumerator->group = group;
+        enumerator->seal = _PR_ENUM_SEALED;
+    }
+    return enumerator;
+}  /* PR_CreateMWaitEnumerator */
+
+PR_IMPLEMENT(PRStatus) PR_DestroyMWaitEnumerator(PRMWaitEnumerator* enumerator)
+{
+    PR_ASSERT(NULL != enumerator);
+    PR_ASSERT(_PR_ENUM_SEALED == enumerator->seal);
+    if ((NULL == enumerator) || (_PR_ENUM_SEALED != enumerator->seal))
+    {
+        PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+        return PR_FAILURE;
+    }
+    enumerator->seal = _PR_ENUM_UNSEALED;
+    PR_Free(enumerator);
+    return PR_SUCCESS;
+}  /* PR_DestroyMWaitEnumerator */
+
+PR_IMPLEMENT(PRRecvWait*) PR_EnumerateWaitGroup(
+    PRMWaitEnumerator *enumerator, const PRRecvWait *previous)
+{
+    PRRecvWait *result = NULL;
+    
+    /* entry point sanity checking */
+    PR_ASSERT(NULL != enumerator);
+    PR_ASSERT(_PR_ENUM_SEALED == enumerator->seal);
+    if ((NULL == enumerator)
+    || (_PR_ENUM_SEALED != enumerator->seal)) goto bad_argument;
+
+    /* beginning of enumeration */
+    if (NULL == previous)
+    {
+        if (NULL == enumerator->group)
+        {
+            enumerator->group = mw_state->group;
+            if (NULL == enumerator->group)
+            {
+                PR_SetError(PR_GROUP_EMPTY_ERROR, 0);
+                return NULL;
+            }
+        }
+        enumerator->waiter = &enumerator->group->waiter->recv_wait;
+        enumerator->p_timestamp = enumerator->group->p_timestamp;
+        enumerator->thread = PR_GetCurrentThread();
+        enumerator->index = 0;
+    }
+    /* continuing an enumeration */
+    else
+    {
+        PRThread *me = PR_GetCurrentThread();
+        PR_ASSERT(me == enumerator->thread);
+        if (me != enumerator->thread) goto bad_argument;
+
+        /* need to restart the enumeration */
+        if (enumerator->p_timestamp != enumerator->group->p_timestamp)
+            return PR_EnumerateWaitGroup(enumerator, NULL);
+    }
+
+    /* actually progress the enumeration */
+#if defined(WINNT)
+    _PR_MD_LOCK(&enumerator->group->mdlock);
+#else
+    PR_Lock(enumerator->group->ml);
+#endif
+    while (enumerator->index++ < enumerator->group->waiter->length)
+    {
+        if (NULL != (result = *(enumerator->waiter)++)) break;
+    }
+#if defined(WINNT)
+    _PR_MD_UNLOCK(&enumerator->group->mdlock);
+#else
+    PR_Unlock(enumerator->group->ml);
+#endif
+
+    return result;  /* what we live for */
+
+bad_argument:
+    PR_SetError(PR_INVALID_ARGUMENT_ERROR, 0);
+    return NULL;  /* probably ambiguous */
+}  /* PR_EnumerateWaitGroup */
+
+/* prmwait.c */