openmpi/orte/runtime/orte_wait.c

/*
 * Copyright (c) 2004-2005 The Trustees of Indiana University and Indiana
 *                         University Research and Technology
 *                         Corporation.  All rights reserved.
 * Copyright (c) 2004-2008 The University of Tennessee and The University
 *                         of Tennessee Research Foundation.  All rights
 *                         reserved.
 * Copyright (c) 2004-2005 High Performance Computing Center Stuttgart, 
 *                         University of Stuttgart.  All rights reserved.
 * Copyright (c) 2004-2005 The Regents of the University of California.
 *                         All rights reserved.
 * Copyright (c) 2007      Los Alamos National Security, LLC.  All rights
 *                         reserved. 
 * Copyright (c) 2008      Institut National de Recherche en Informatique
 *                         et Automatique. All rights reserved.
 * $COPYRIGHT$
 * 
 * Additional copyrights may follow
 * 
 * $HEADER$
 */


#include "orte_config.h"
#include "orte/constants.h"

#include <assert.h>
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_QUEUE_H
#include <sys/queue.h>
#endif
#include <errno.h>
#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif
#ifdef HAVE_SYS_TYPES_H
#include <sys/types.h>
#endif
#include <fcntl.h>
#include <stdlib.h>
#include <signal.h>
#include <stdio.h>
#include <sys/stat.h>
#ifdef HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif

#include "opal/dss/dss_types.h"
#include "opal/class/opal_object.h"
#include "opal/class/opal_list.h"
#include "opal/event/event.h"
#include "opal/threads/mutex.h"
#include "opal/threads/condition.h"
#include "opal/sys/atomic.h"

#include "orte/util/show_help.h"
#include "orte/mca/errmgr/errmgr.h"
#include "orte/util/name_fns.h"
#include "orte/runtime/orte_globals.h"

#include "orte/runtime/orte_wait.h"


/*********************************************************************
*
* Wait Object Declarations
*
********************************************************************/
static void message_event_destructor(orte_message_event_t *ev)
{
    if (NULL != ev->ev) {
        free(ev->ev);
    }
    if (NULL != ev->buffer) {
        OBJ_RELEASE(ev->buffer);
    }
#if OMPI_ENABLE_DEBUG
    if (NULL != ev->file) {
        free(ev->file);
    }
#endif
}

static void message_event_constructor(orte_message_event_t *ev)
{
    ev->ev = (opal_event_t*)malloc(sizeof(opal_event_t));
    ev->buffer = OBJ_NEW(opal_buffer_t);
#if OMPI_ENABLE_DEBUG
    ev->file = NULL;
#endif
}

OBJ_CLASS_INSTANCE(orte_message_event_t,
                   opal_object_t,
                   message_event_constructor,
                   message_event_destructor);

static void notify_event_destructor(orte_notify_event_t *ev) 
{ 
    if (NULL != ev->ev) { 
        free(ev->ev); 
    } 
} 
 
static void notify_event_constructor(orte_notify_event_t *ev) 
{ 
    ev->ev = (opal_event_t*)malloc(sizeof(opal_event_t)); 
} 
OBJ_CLASS_INSTANCE(orte_notify_event_t, 
                   opal_object_t, 
                   notify_event_constructor, 
                   notify_event_destructor); 

#ifdef HAVE_WAITPID

static volatile int cb_enabled = true;
static opal_mutex_t mutex;
static opal_list_t pending_pids;
static opal_list_t registered_cb;

/*********************************************************************
 *
 * Local Class Declarations
 *
 ********************************************************************/
struct blk_waitpid_data_t {
    opal_object_t super;
    opal_condition_t *cond;
    volatile int done;
    volatile int status;
    volatile int free;
};
typedef struct blk_waitpid_data_t blk_waitpid_data_t;

struct pending_pids_item_t {
    opal_list_item_t super;
    pid_t pid;
    int status;
};
typedef struct pending_pids_item_t pending_pids_item_t;

struct registered_cb_item_t {
    opal_list_item_t super;
    pid_t pid;
    orte_wait_fn_t callback;
    void *data;
};
typedef struct registered_cb_item_t registered_cb_item_t;

struct waitpid_callback_data_t {
    pid_t pid;
    int status;
    int options;
    pid_t ret;
    opal_mutex_t mutex;
    opal_condition_t cond;
    volatile bool done;
};
typedef struct waitpid_callback_data_t waitpid_callback_data_t;


/*********************************************************************
 *
 * Local Class Definitions
 *
 ********************************************************************/
static void
blk_waitpid_data_construct(opal_object_t *obj)
{
    blk_waitpid_data_t *data = (blk_waitpid_data_t*) obj;

    data->cond = OBJ_NEW(opal_condition_t);
    data->done = 0;
    data->status = 0;
    data->free = 0;
}


static void
blk_waitpid_data_destruct(opal_object_t *obj)
{
    blk_waitpid_data_t *data = (blk_waitpid_data_t*) obj;

    if (NULL != data->cond) OBJ_RELEASE(data->cond);
}


static OBJ_CLASS_INSTANCE(blk_waitpid_data_t, opal_object_t,
                          blk_waitpid_data_construct, 
                          blk_waitpid_data_destruct);

static OBJ_CLASS_INSTANCE(pending_pids_item_t, opal_list_item_t, NULL, NULL);

static OBJ_CLASS_INSTANCE(registered_cb_item_t, opal_list_item_t, NULL, NULL);

static void 
trigger_event_constructor(orte_trigger_event_t *trig)
{
    trig->name = NULL;
    trig->channel = -1;
    opal_atomic_init(&trig->lock, OPAL_ATOMIC_UNLOCKED);
}
static void 
trigger_event_destructor(orte_trigger_event_t *trig)
{
    if (NULL != trig->name) {
        free(trig->name);
    }
}
OBJ_CLASS_INSTANCE(orte_trigger_event_t,
                   opal_object_t,
                   trigger_event_constructor,
                   trigger_event_destructor);

/*********************************************************************
 *
 * Local Variables
 *
 ********************************************************************/
static struct opal_event handler;


/*********************************************************************
 *
 * Local Function Prototypes
 *
 ********************************************************************/
static void blk_waitpid_cb(pid_t wpid, int status, void *data);
static pending_pids_item_t* find_pending_pid(pid_t pid, bool create);
static registered_cb_item_t* find_waiting_cb(pid_t pid, bool create);
static void do_waitall(int options);
static void trigger_callback(registered_cb_item_t *cb, 
                             pending_pids_item_t *pending);
static int register_callback(pid_t pid, orte_wait_fn_t callback,
                             void *data);
static int unregister_callback(pid_t pid);
void orte_wait_signal_callback(int fd, short event, void *arg);
static pid_t internal_waitpid(pid_t pid, int *status, int options);
#if  OMPI_THREADS_HAVE_DIFFERENT_PIDS
static void internal_waitpid_callback(int fd, short event, void *arg);
#endif

/*********************************************************************
 *
 * Interface Functions
 *
 ********************************************************************/

void
orte_wait_disable(void)
{
    opal_event_del(&handler);
}

void
orte_wait_enable(void)
{
    opal_event_add(&handler, NULL);
}

int
orte_wait_init(void)
{
    OBJ_CONSTRUCT(&mutex, opal_mutex_t);
    OBJ_CONSTRUCT(&pending_pids, opal_list_t);
    OBJ_CONSTRUCT(&registered_cb, opal_list_t);

    opal_event_set(&handler, SIGCHLD, OPAL_EV_SIGNAL|OPAL_EV_PERSIST,
                   orte_wait_signal_callback,
                   &handler);

    opal_event_add(&handler, NULL);
    return ORTE_SUCCESS;
}


int
orte_wait_finalize(void)
{
    opal_list_item_t *item;

    OPAL_THREAD_LOCK(&mutex);
    opal_event_del(&handler);

    /* clear out the lists */
    while (NULL != (item = opal_list_remove_first(&pending_pids))) {
        OBJ_RELEASE(item);
    }
    while (NULL != (item = opal_list_remove_first(&registered_cb))) {
        OBJ_RELEASE(item);
    }
    OPAL_THREAD_UNLOCK(&mutex);

    OBJ_DESTRUCT(&mutex);
    OBJ_DESTRUCT(&pending_pids);
    OBJ_DESTRUCT(&registered_cb);

    return ORTE_SUCCESS;
}

int 
orte_wait_kill(int sig)
{
    opal_list_item_t* item;

    OPAL_THREAD_LOCK(&mutex);
    do_waitall(0);
    while (NULL != (item = opal_list_remove_first(&registered_cb))) {
        registered_cb_item_t *cb = (registered_cb_item_t*)item;
        pending_pids_item_t *pending = find_pending_pid(cb->pid,false);
        if(NULL == pending) {
            int status;
            kill(cb->pid, sig);
            waitpid(cb->pid,&status,0);
        } else {
            OBJ_RELEASE(pending);
        }
        OBJ_RELEASE(item);
    } 
    OPAL_THREAD_UNLOCK(&mutex);
    return ORTE_SUCCESS;
}


pid_t
orte_waitpid(pid_t wpid, int *status, int options)
{
    pending_pids_item_t *pending = NULL;
    blk_waitpid_data_t *data = NULL;
    struct timespec spintime;
    pid_t ret;

    if ((wpid <= 0) || (0 != (options & WUNTRACED))) {
        errno = ORTE_ERR_NOT_IMPLEMENTED;
        return (pid_t) -1;
    }

    OPAL_THREAD_LOCK(&mutex);

    do_waitall(options);
    pending = find_pending_pid(wpid, false);
    if (NULL != pending) {
        *status = pending->status;
        ret = pending->pid;
        opal_list_remove_item(&pending_pids, (opal_list_item_t*) pending);
        OBJ_RELEASE(pending);
        goto cleanup;
    }

    if (0 == (options & WNOHANG)) {
        /* blocking - create a blk_waitpid_data_t, register the
           callback with it, and wait for the trigger.  Hold mutex
           until after we register so that waitpid isn't called before
           the callback is registered.  There is a race condition
           between starting to sit in the condition_wait and the
           callback being triggered, so poll for completion on the
           event just in case. */
        data = OBJ_NEW(blk_waitpid_data_t);
        if (NULL == data) {
            ret = -1;
            goto cleanup;
        }

        register_callback(wpid, blk_waitpid_cb, data);
        
        while (0 == data->done) {
            spintime.tv_sec = 0;
            spintime.tv_nsec = 1 * 1000 * 1000; /* 1 milliseconds */
            opal_condition_timedwait(data->cond, 
                                     &mutex, 
                                     &spintime);

            /* if we have pthreads and progress threads and we are the
               event thread, opal_condition_timedwait won't progress
               anything, so we need to do it. */
#if OMPI_HAVE_POSIX_THREADS && OMPI_ENABLE_PROGRESS_THREADS
            if (opal_using_threads()) {
                opal_mutex_unlock(&mutex);
                opal_event_loop(OPAL_EVLOOP_NONBLOCK);
                opal_mutex_lock(&mutex);
            }
#endif            
	    do_waitall(0);
        }

        ret = wpid;
        *status = data->status;

        /* Unlock the mutex first, so as to not cause any deadlocks.
           We aren't going to touch any variables that could cause
           problems with thread badness, so it's ok to be here without
           the thread locked.  Wich is also the reason we go to done
           instead of cleanup. */
        OPAL_THREAD_UNLOCK(&mutex);

        while (0 == data->free) {
            /* don't free the condition variable until we are positive
               that the broadcast is done being sent.  Otherwise,
               pthreads gets really unhappy when we pull the rug out
               from under it. Yes, it's spinning.  No, we won't spin
               for long. */

            if (!OMPI_HAVE_THREAD_SUPPORT || opal_event_progress_thread()) {
                opal_event_loop(OPAL_EVLOOP_NONBLOCK);
            }
        }

        OBJ_RELEASE(data);
        /* see note above while loop for why we jump to done */
        goto done;

    } else {
        /* non-blocking - return what waitpid would */
        ret = internal_waitpid(wpid, status, options);
    }

 cleanup:
    OPAL_THREAD_UNLOCK(&mutex);

 done:
    return ret;
}

int
orte_wait_cb(pid_t wpid, orte_wait_fn_t callback, void *data)
{
    int ret;

    if (wpid <= 0) return ORTE_ERR_NOT_IMPLEMENTED;
    if (NULL == callback) return ORTE_ERR_BAD_PARAM;

    OPAL_THREAD_LOCK(&mutex);
    ret = register_callback(wpid, callback, data);
    do_waitall(0);
    OPAL_THREAD_UNLOCK(&mutex);

    return ret;
}


int
orte_wait_cb_cancel(pid_t wpid)
{
    int ret;

    if (wpid <= 0) return ORTE_ERR_BAD_PARAM;

    OPAL_THREAD_LOCK(&mutex);
    do_waitall(0);
    ret = unregister_callback(wpid);
    OPAL_THREAD_UNLOCK(&mutex);

    return ret;
}


/* callback from the event library whenever a SIGCHLD is received */
void
orte_wait_signal_callback(int fd, short event, void *arg)
{
    struct opal_event *signal = (struct opal_event*) arg;

    if (SIGCHLD != OPAL_EVENT_SIGNAL(signal)) return;

    OPAL_THREAD_LOCK(&mutex);
    do_waitall(0);
    OPAL_THREAD_UNLOCK(&mutex);
}


int
orte_wait_cb_disable()
{
    OPAL_THREAD_LOCK(&mutex);
    do_waitall(0);
    cb_enabled = false;
    OPAL_THREAD_UNLOCK(&mutex);

    return ORTE_SUCCESS;
}


int
orte_wait_cb_enable()
{
    OPAL_THREAD_LOCK(&mutex);
    cb_enabled = true;
    do_waitall(0);
    OPAL_THREAD_UNLOCK(&mutex);

    return ORTE_SUCCESS;
}


int orte_wait_event(opal_event_t **event, orte_trigger_event_t *trig,
                    char *trigger_name,
                    void (*cbfunc)(int, short, void*))
{
    int p[2];
    
    if (pipe(p) < 0) {
        ORTE_ERROR_LOG(ORTE_ERR_SYS_LIMITS_PIPES);
        return ORTE_ERR_SYS_LIMITS_PIPES;
    }

    /* save the trigger name */
    trig->name = strdup(trigger_name);
    
    /* create the event */
    *event = (opal_event_t*)malloc(sizeof(opal_event_t));
    
    /* pass back the write end of the pipe */
    trig->channel = p[1];
    
    /* define the event to fire when someone writes to the pipe */
    opal_event_set(*event, p[0], OPAL_EV_READ, cbfunc, NULL);
    
	/* Add it to the active events, without a timeout */
	opal_event_add(*event, NULL);

    /* all done */
    return ORTE_SUCCESS;
}


void orte_trigger_event(orte_trigger_event_t *trig)
{
    int data=1;
    
    OPAL_OUTPUT_VERBOSE((1, orte_debug_output,
                        "%s calling %s trigger",
                         ORTE_NAME_PRINT(ORTE_PROC_MY_NAME),
                         trig->name));
    
    /* if we already fired it, don't do it again - this automatically
     * records that we did fire it
     */
    if (!opal_atomic_trylock(&trig->lock)) { /* returns 1 if already locked */
        return;
    }
    
    write(trig->channel, &data, sizeof(int));
    close(trig->channel);
    opal_progress();
}


/*********************************************************************
 *
 * Local Functions
 *
 * None of these functions should lock mutex.  All but blk_waitpid_cb
 * should only be called if the mutex is already locked.
 *
 ********************************************************************/
static void
blk_waitpid_cb(pid_t wpid, int status, void *data)
{
    blk_waitpid_data_t *wp_data = (blk_waitpid_data_t*) data;

    wp_data->status = status;
    wp_data->done = 1;
    opal_condition_signal(wp_data->cond);
    wp_data->free = 1;
}


/* -1 will return the first available pid */
static pending_pids_item_t *
find_pending_pid(pid_t pid, bool create)
{
    opal_list_item_t *item;
    pending_pids_item_t *pending;

    for (item = opal_list_get_first(&pending_pids) ;
         item != opal_list_get_end(&pending_pids) ;
         item = opal_list_get_next(item)) {
        pending = (pending_pids_item_t*) item;

        if (pending->pid == pid || -1 == pid) {
            return pending;
        }
    }

    if (create) {
        pending = OBJ_NEW(pending_pids_item_t);
        if (NULL == pending) return NULL;

        pending->pid = pid;
        pending->status = 0;
        opal_list_append(&pending_pids, (opal_list_item_t*) pending);
        return pending;
    } 

    return NULL;
}


/* pid must be positive */
static registered_cb_item_t *
find_waiting_cb(pid_t pid, bool create)
{
    opal_list_item_t *item = NULL;
    registered_cb_item_t *reg_cb = NULL;

    for (item = opal_list_get_first(&registered_cb) ;
         item != opal_list_get_end(&registered_cb) ;
         item = opal_list_get_next(item)) {
        reg_cb = (registered_cb_item_t*) item;

        if (reg_cb->pid == pid) {
            return reg_cb;
        }
    }

    if (create) {
        reg_cb = OBJ_NEW(registered_cb_item_t);
        if (NULL == reg_cb) return NULL;

        reg_cb->pid = pid;
        reg_cb->callback = NULL;
        reg_cb->data = NULL;
        opal_list_append(&registered_cb, (opal_list_item_t*) reg_cb);
        return reg_cb;
    }

    return NULL;
}


static void
do_waitall(int options)
{
    if (!cb_enabled) return;
    while (1) {
        int status;
        pid_t ret = internal_waitpid(-1, &status, WNOHANG);
        pending_pids_item_t *pending;
        registered_cb_item_t *cb;

        if (-1 == ret && EINTR == errno) continue;
        if (ret <= 0) break;

        cb = find_waiting_cb(ret, false);
        if (NULL == cb) {
            pending = OBJ_NEW(pending_pids_item_t);
            pending->pid = ret;
            pending->status = status;
            opal_list_append(&pending_pids, &pending->super);
        } else {
            opal_list_remove_item(&registered_cb, &cb->super);
            OPAL_THREAD_UNLOCK(&mutex);
            cb->callback(cb->pid, status, cb->data);
            OPAL_THREAD_LOCK(&mutex);
            OBJ_RELEASE(cb);
        }
    }
}


static void
trigger_callback(registered_cb_item_t *cb, pending_pids_item_t *pending)
{
    assert(cb->pid == pending->pid);

    OPAL_THREAD_UNLOCK(&mutex);
    cb->callback(cb->pid, pending->status, cb->data);
    OPAL_THREAD_LOCK(&mutex);

    opal_list_remove_item(&pending_pids, (opal_list_item_t*) pending);
    opal_list_remove_item(&registered_cb, (opal_list_item_t*) cb);
}


static int
register_callback(pid_t pid, orte_wait_fn_t callback, void *data)
{
    registered_cb_item_t *reg_cb;
    pending_pids_item_t *pending;

    /* register the callback */
    reg_cb = find_waiting_cb(pid, true);
    if (NULL == reg_cb) return ORTE_ERROR;
    if (NULL != reg_cb->callback) return ORTE_EXISTS;

    reg_cb->callback = callback;
    reg_cb->data = data;

    /* make sure we shouldn't trigger right now */
    pending = find_pending_pid(pid, false);
    if (NULL != pending) {
        trigger_callback(reg_cb, pending);
    }
    return ORTE_SUCCESS;
}


static int
unregister_callback(pid_t pid)
{
    registered_cb_item_t *reg_cb;

    /* register the callback */
    reg_cb = find_waiting_cb(pid, false);
    if (NULL == reg_cb) return ORTE_ERR_BAD_PARAM;

    opal_list_remove_item(&registered_cb, (opal_list_item_t*) reg_cb);

    return ORTE_SUCCESS;
}



static pid_t
internal_waitpid(pid_t pid, int *status, int options)
{
#if  OMPI_THREADS_HAVE_DIFFERENT_PIDS
    waitpid_callback_data_t data;
    struct timeval tv;
    struct opal_event ev;

    if (opal_event_progress_thread()) {
        /* I already am the progress thread.  no need to event me */
        return waitpid(pid, status, options);
    }

    data.done = false;
    data.pid = pid;
    data.options = options;
    OBJ_CONSTRUCT(&(data.mutex), opal_mutex_t);
    OBJ_CONSTRUCT(&(data.cond), opal_condition_t);

    OPAL_THREAD_LOCK(&(data.mutex));

    tv.tv_sec = 0;
    tv.tv_usec = 0;

    opal_evtimer_set(&ev, internal_waitpid_callback, &data);
    opal_evtimer_add(&ev, &tv);

    while (data.done == false) {
        opal_condition_wait(&(data.cond), &(data.mutex));
    }

    OPAL_THREAD_UNLOCK(&(data.mutex));

    OBJ_DESTRUCT(&(data.cond));
    OBJ_DESTRUCT(&(data.mutex));

    *status = data.status;
    return data.ret;
    
#else
    return waitpid(pid, status, options);
#endif
}


#if  OMPI_THREADS_HAVE_DIFFERENT_PIDS
static void
internal_waitpid_callback(int fd, short event, void *arg)
{
    waitpid_callback_data_t *data = (waitpid_callback_data_t*) arg;

    data->ret = waitpid(data->pid, &(data->status), data->options);

    data->done = true;
    opal_condition_signal(&(data->cond));
}
#endif

#elif defined(__WINDOWS__)

/*********************************************************************
 *
 * Local Variables
 *
 ********************************************************************/

static volatile int cb_enabled = true;
static opal_mutex_t mutex;
static opal_list_t pending_pids;
static opal_list_t registered_cb;

/*********************************************************************
 *
 * Local Class Declarations
 *
 ********************************************************************/

typedef struct {
    opal_list_item_t super;
    pid_t pid;
    HANDLE registered_handle;
    orte_wait_fn_t callback;
    void *data;
    int status;
} opal_process_handle_t;


/*********************************************************************
 *
 * Local Class Definitions
 *
 ********************************************************************/

static void opal_process_handle_construct( opal_object_t* obj )
{
    opal_process_handle_t* handle = (opal_process_handle_t*)obj;

    handle->registered_handle = INVALID_HANDLE_VALUE;
    handle->pid               = 0;
    handle->callback          = NULL;
    handle->data              = NULL;
}

static void opal_process_handle_destruct( opal_object_t* obj )
{
    opal_process_handle_t* handle = (opal_process_handle_t*)obj;

    if( INVALID_HANDLE_VALUE != handle->registered_handle ) {
        if( 0 == UnregisterWait( handle->registered_handle ) ) {
            int error = GetLastError();
        }
        if( 0 == CloseHandle( handle->registered_handle ) ) {
            int error = GetLastError();
        }
        handle->registered_handle = INVALID_HANDLE_VALUE;
    }
}

static OBJ_CLASS_INSTANCE( opal_process_handle_t, opal_list_item_t,
                           opal_process_handle_construct, opal_process_handle_destruct );

static void 
trigger_event_constructor(orte_trigger_event_t *trig)
{
    trig->name = NULL;
    trig->channel = -1;
    opal_atomic_init(&trig->lock, OPAL_ATOMIC_UNLOCKED);
}
static void 
trigger_event_destructor(orte_trigger_event_t *trig)
{
    if (NULL != trig->name) {
        free(trig->name);
    }
}
OBJ_CLASS_INSTANCE(orte_trigger_event_t,
                   opal_object_t,
                   trigger_event_constructor,
                   trigger_event_destructor);

/*********************************************************************
 *
 * Interface Functions
 *
 ********************************************************************/

int
orte_wait_init(void)
{
    OBJ_CONSTRUCT(&mutex, opal_mutex_t);
    OBJ_CONSTRUCT(&registered_cb, opal_list_t);
    OBJ_CONSTRUCT(&pending_pids, opal_list_t);
    return ORTE_SUCCESS;
}

int
orte_wait_finalize(void)
{
    opal_list_item_t* item;

    OPAL_THREAD_LOCK(&mutex);
    OPAL_THREAD_UNLOCK(&mutex);

    while (NULL != (item = opal_list_remove_first(&pending_pids))) {
        OBJ_RELEASE(item);
    }
    while (NULL != (item = opal_list_remove_first(&registered_cb))) {
        OBJ_RELEASE(item);
    }

    OBJ_DESTRUCT(&mutex);
    OBJ_DESTRUCT(&registered_cb);
    OBJ_DESTRUCT(&pending_pids);

    return ORTE_SUCCESS;
}

void orte_trigger_event(orte_trigger_event_t *trig)
{
    int data=1;
    
    OPAL_OUTPUT_VERBOSE((1, orte_debug_output,
                         "%s calling %s trigger",
                         ORTE_NAME_PRINT(ORTE_PROC_MY_NAME),
                         trig->name));
    
    if (!opal_atomic_trylock(&trig->lock)) { /* returns 1 if already locked */
        return;
    }
        
    send(trig->channel, (const char*)&data, sizeof(int), 0);
    closesocket(trig->channel);
    opal_progress();
}


/**
 * Internal function which find a corresponding process structure
 * based on the pid. If create is true and the pid does not have a
 * corresponding process structure, one will be automatically
 * created and attached to the end of the list.
 */
static opal_process_handle_t* opal_find_pid_in_list(opal_list_t* list, pid_t pid, bool create)
{
    opal_list_item_t *item = NULL;
    opal_process_handle_t *handle = NULL;

    for (item = opal_list_get_first(list) ;
         item != opal_list_get_end(list) ;
         item = opal_list_get_next(item)) {
        handle = (opal_process_handle_t*) item;

        if (handle->pid == pid) {
            return handle;
        }
    }

    if (create) {
        handle = OBJ_NEW(opal_process_handle_t);
        if (NULL == handle) return NULL;

        handle->pid = pid;
        handle->callback = NULL;
        handle->data = NULL;
        opal_list_append(list, (opal_list_item_t*)handle);
        return handle;
    }

    return NULL;
}
#define find_pending_pid(PID, CREATE)  opal_find_pid_in_list( &pending_pids, (PID), (CREATE) )
#define find_pending_cb(PID, CREATE)   opal_find_pid_in_list( &registered_cb, (PID), (CREATE) )

pid_t
orte_waitpid(pid_t wpid, int *status, int options)
{
    opal_process_handle_t* pending;

    OPAL_THREAD_LOCK(&mutex);

    /**
     * Is the child already gone ?
     */
    pending = find_pending_pid( wpid, false );
    if( NULL != pending ) {
        *status = pending->status;
        opal_list_remove_item( &pending_pids, (opal_list_item_t*)pending );
        OBJ_RELEASE(pending);
        OPAL_THREAD_UNLOCK(&mutex);
        return wpid;
    }

    /**
     * Do we have any registered callback for this particular pid ?
     */
    pending = find_pending_cb( wpid, false );
    if( NULL != pending ) {
        opal_list_remove_item( &registered_cb, (opal_list_item_t*)pending );
        OBJ_RELEASE( pending );
    }

    /**
     * No luck so far. Wait until the process complete ...
     */
    if( WAIT_OBJECT_0 == WaitForSingleObject( (HANDLE)wpid, INFINITE ) ) {
        DWORD exitCode;
        /* Process completed. Grab the exit value and return. */
        if( 0 == GetExitCodeProcess( (HANDLE)wpid, &exitCode ) ) {
            int error = GetLastError();
        }
        *status = (int)exitCode;
    }
    OPAL_THREAD_UNLOCK(&mutex);
    return wpid;
}

static void CALLBACK trigger_process_detection( void* lpParameter, BOOLEAN TimerOrWaitFired )
{
    opal_process_handle_t* handle = (opal_process_handle_t*)lpParameter;
    DWORD exitCode;

    opal_list_remove_item( &registered_cb, (opal_list_item_t*)handle );
    /**
     * As this item will never be triggered again, we can safely remove the
     * registered handle.
     */
    if( 0 == UnregisterWait( handle->registered_handle ) ) {
		/**
		 * If any callback functions associated with the timer have not completed when
		 * UnregisterWait is called, UnregisterWait unregisters the wait on the callback
		 * functions and fails with the ERROR_IO_PENDING error code. The error code does
		 * not indicate that the function has failed, and the function does not need to
		 * be called again. If your code requires an error code to set only when the
		 * unregister operation has failed, call UnregisterWaitEx instead.
		 */
        int error = GetLastError();
    }
    handle->registered_handle = INVALID_HANDLE_VALUE;
    /**
     * Get the exit code of the process.
     */
    if( 0 == GetExitCodeProcess( (HANDLE)handle->pid, &exitCode ) ) {
        int error = GetLastError();
    }
    handle->status = (int)exitCode;
    handle->callback(handle->pid, handle->status, handle->data);
    OBJ_RELEASE( handle );
}

int
orte_wait_cb(pid_t wpid, orte_wait_fn_t callback, void *data)
{
    opal_process_handle_t* handle;

    if (wpid <= 0) return ORTE_ERR_NOT_IMPLEMENTED;
    if (NULL == callback) return ORTE_ERR_BAD_PARAM;

    OPAL_THREAD_LOCK(&mutex);
    handle = find_pending_pid(wpid, false);
    if( handle != NULL ) {
        opal_list_remove_item( &pending_pids, (opal_list_item_t*)handle );
        OBJ_RELEASE(handle);
        return ORTE_SUCCESS;
    }
    handle = find_pending_cb( wpid, true );
    handle->pid = wpid;
    handle->callback = callback;
    handle->data = data;

    if( false == RegisterWaitForSingleObject( &handle->registered_handle, (HANDLE)handle->pid, 
                                              trigger_process_detection, (void*)handle, INFINITE,
                                              WT_EXECUTEONLYONCE | WT_EXECUTELONGFUNCTION) ) {
        DWORD errcode = GetLastError();
        char* localbuf = NULL;

        FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM,
                       NULL, errcode, 0, (LPTSTR)&localbuf, 1024, NULL );
        opal_output( 0, "Failed to initialize the process callback for pid %lu error %s\n",
                        (unsigned long)(handle->pid), localbuf );
        LocalFree( localbuf );
    }

    OPAL_THREAD_UNLOCK(&mutex);

    return OPAL_SUCCESS;
}

int
orte_wait_cb_cancel(pid_t wpid)
{
    opal_process_handle_t* pending;

    OPAL_THREAD_LOCK(&mutex);

    /**
     * Do we have any registered callback for this particular pid ?
     */
    pending = find_pending_cb( wpid, false );
    if( NULL != pending ) {
        opal_list_remove_item( &registered_cb, (opal_list_item_t*)pending );
        OBJ_RELEASE( pending );
        OPAL_THREAD_UNLOCK(&mutex);
        return ORTE_SUCCESS;
    }
    OPAL_THREAD_UNLOCK(&mutex);
    return ORTE_ERR_BAD_PARAM;
}

int
orte_wait_cb_disable(void)
{
    OPAL_THREAD_LOCK(&mutex);
    cb_enabled = false;
    OPAL_THREAD_UNLOCK(&mutex);

    return ORTE_SUCCESS;
}

int
orte_wait_cb_enable(void)
{
    OPAL_THREAD_LOCK(&mutex);
    cb_enabled = true;
    OPAL_THREAD_UNLOCK(&mutex);

    return ORTE_SUCCESS;
}


int orte_wait_event(opal_event_t **event, orte_trigger_event_t *trig,
                    char *trigger_name,
                    void (*cbfunc)(int, short, void*))
{
    int p[2];
    
    if (evutil_socketpair(AF_UNIX, SOCK_STREAM, 0, p) == -1) {
        return ORTE_ERROR;
    }

    /* save the trigger name */
    trig->name = strdup(trigger_name);
    
    /* create the event */
    *event = (opal_event_t*)malloc(sizeof(opal_event_t));
    
    /* setup the trigger and its associated lock */
    OBJ_CONSTRUCT(trig, orte_trigger_event_t);
    
    /* pass back the write end of the pipe */
    trig->channel = p[1];
    
    /* define the event to fire when someone writes to the pipe */
    opal_event_set(*event, p[0], OPAL_EV_READ, cbfunc, NULL);
    
	/* Add it to the active events, without a timeout */
	opal_event_add(*event, NULL);

    /* all done */
    return ORTE_SUCCESS;
}


int
orte_wait_kill(int sig)
{
    opal_list_item_t* item;

    /**
     * First pass. For all registered processes not yet triggered, terminate the
     * process. Once this first pass is done, we will try to cleanup the ressources
     */
    OPAL_THREAD_LOCK(&mutex);

    for (item = opal_list_get_first(&registered_cb) ;
         item != opal_list_get_end(&registered_cb) ;
         item = opal_list_get_next(item)) {
        opal_process_handle_t* handle = (opal_process_handle_t*)item;

        if( 0 == TerminateProcess( (HANDLE)handle->pid, sig ) ) {
            int error = GetLastError();
        }
    }

    /* Give them a chance to complete the kill. */
    SleepEx( 1000, TRUE );

    /* And now clean all ressources. */
    while (NULL != (item = opal_list_remove_first(&registered_cb))) {
        OBJ_RELEASE(item);
    }
    while (NULL != (item = opal_list_remove_first(&pending_pids))) {
        OBJ_RELEASE(item);
    }

    OPAL_THREAD_UNLOCK(&mutex);
    return ORTE_SUCCESS;
}

#else /* no waitpid and not windows */

int
orte_wait_init(void) {
    return ORTE_SUCCESS;
}

int
orte_wait_finalize(void)
{
    return ORTE_SUCCESS;
}

pid_t
orte_waitpid(pid_t wpid, int *status, int options)
{
    return ORTE_ERR_NOT_SUPPORTED;
}

int
orte_wait_cb(pid_t wpid, orte_wait_fn_t callback, void *data)
{
    return ORTE_ERR_NOT_SUPPORTED;
}

int
orte_wait_cb_cancel(pid_t wpid)
{
    return ORTE_ERR_NOT_SUPPORTED;
}

int
orte_wait_cb_disable(void)
{
    return ORTE_ERR_NOT_SUPPORTED;
}

int
orte_wait_cb_enable(void)
{
    return ORTE_ERR_NOT_SUPPORTED;
}

void orte_trigger_event(orte_trigger_event_t *trig)
{
}

int
orte_wait_event(opal_event_t **event, int *trig,
                char *trigger_name,
                void (*cbfunc)(int, short, void*))
{
    return ORTE_ERR_NOT_SUPPORTED;
}

int
orte_wait_kill(int sig)
{
    return ORTE_ERR_NOT_SUPPORTED;
}

#endif