/* -*- Mode: C; c-basic-offset:4 ; indent-tabs-mode:nil ; -*- */

/*

 *  (C) 2006 by Argonne National Laboratory.

 *      See COPYRIGHT in top-level directory.

 */

#ifndef MPIU_PROCESS_WRAPPERS_H_INCLUDED

#define MPIU_PROCESS_WRAPPERS_H_INCLUDED

/* MPIU_PW --> MPI Util Process Wrapper */

#include "mpichconf.h"

/* MPIU_PW_SCHED_YIELD() - Yield the processor to OS scheduler */

/* On a typical Linux system (verified with kernels 3.2 and 3.5),

 * usleep has a resolution of more than 1000 cycles. This makes

 * it impractical if the desired sleeping period is shorter. On

 * the other hand, sleep(0) returns immediately without going to

 * the kernel. This means that there is no actual yielding, which

 * is equivalent to doing nothing. Thus, usleep and sleep are not

 * recommended as ways to yield the CPU, and sched_yield would be

 * preferred if available.

 * Note that nanosleep has the same shortcomings as usleep.*/

#if defined(USE_SWITCHTOTHREAD_FOR_YIELD)

    #include <winsock2.h>

    #include <windows.h>

    #define MPIU_PW_Sched_yield() SwitchToThread()

#elif defined(USE_WIN32_SLEEP_FOR_YIELD)

    #include <winsock2.h>

    #include <windows.h>

    #define MPIU_PW_Sched_yield() Sleep(0)

#elif defined(USE_SCHED_YIELD_FOR_YIELD)

    #ifdef HAVE_SCHED_H

        #include <sched.h>

    #endif

    #define MPIU_PW_Sched_yield() sched_yield()

#elif defined(USE_YIELD_FOR_YIELD)

    #ifdef HAVE_SCHED_H

        #include <sched.h>

    #endif

    #define MPIU_PW_Sched_yield() yield()

#elif defined (USE_SELECT_FOR_YIELD)

    #ifdef HAVE_SYS_SELECT_H

        #include <sys/select.h>

    #endif

    #define MPIU_PW_Sched_yield() do { struct timeval t; t.tv_sec = 0; t.tv_usec = 0; select(0,0,0,0,&t); } while (0)

#elif defined (USE_USLEEP_FOR_YIELD)

    #ifdef HAVE_UNISTD_H

        #include <unistd.h>

        #if defined (NEEDS_USLEEP_DECL)

        int usleep(useconds_t usec);

        #endif

    #endif

    #define MPIU_PW_Sched_yield() usleep(0)

#elif defined (USE_SLEEP_FOR_YIELD)

    #ifdef HAVE_UNISTD_H

        #include <unistd.h>

    #endif

    #define MPIU_PW_Sched_yield() sleep(0)

#elif defined (USE_NOTHING_FOR_YIELD)

    #define MPIU_PW_Sched_yield() do {} while (0)

#else

    #error "No mechanism available to yield"

#endif

#endif /* MPIU_PROCESS_WRAPPERS_H_INCLUDED */