source: downloads/tcl8.5.2/compat/waitpid.c @ 37

/* 
 * waitpid.c --
 *
 *      This procedure emulates the POSIX waitpid kernel call on BSD systems
 *      that don't have waitpid but do have wait3. This code is based on a
 *      prototype version written by Mark Diekhans and Karl Lehenbauer.
 *
 * Copyright (c) 1993 The Regents of the University of California.
 * Copyright (c) 1994 Sun Microsystems, Inc.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 *
 * RCS: @(#) $Id: waitpid.c,v 1.5 2007/04/16 13:36:35 dkf Exp $
 */

#include "tclPort.h"

#ifndef pid_t
#define pid_t int
#endif

/*
 * A linked list of the following structures is used to keep track of
 * processes for which we received notification from the kernel, but the
 * application hasn't waited for them yet (this can happen because wait may
 * not return the process we really want). We save the information here until
 * the application finally does wait for the process.
 */

typedef struct WaitInfo {
    pid_t pid;                  /* Pid of process that exited. */
    WAIT_STATUS_TYPE status;    /* Status returned when child exited or
                                 * suspended. */
    struct WaitInfo *nextPtr;   /* Next in list of exited processes. */
} WaitInfo;

static WaitInfo *deadList = NULL;
                                /* First in list of all dead processes. */

/*
 *----------------------------------------------------------------------
 *
 * waitpid --
 *
 *      This procedure emulates the functionality of the POSIX waitpid kernel
 *      call, using the BSD wait3 kernel call. Note: it doesn't emulate
 *      absolutely all of the waitpid functionality, in that it doesn't
 *      support pid's of 0 or < -1.
 *
 * Results:
 *      -1 is returned if there is an error in the wait kernel call. Otherwise
 *      the pid of an exited or suspended process is returned and *statusPtr
 *      is set to the status value of the process.
 *
 * Side effects:
 *      None.
 *
 *----------------------------------------------------------------------
 */

#ifdef waitpid
#   undef waitpid
#endif

pid_t
waitpid(
    pid_t pid,                  /* The pid to wait on. Must be -1 or greater
                                 * than zero. */
    int *statusPtr,             /* Where to store wait status for the
                                 * process. */
    int options)                /* OR'ed combination of WNOHANG and
                                 * WUNTRACED. */
{
    register WaitInfo *waitPtr, *prevPtr;
    pid_t result;
    WAIT_STATUS_TYPE status;

    if ((pid < -1) || (pid == 0)) {
        errno = EINVAL;
        return -1;
    }

    /*
     * See if there's a suitable process that has already stopped or exited.
     * If so, remove it from the list of exited processes and return its
     * information.
     */

    for (waitPtr = deadList, prevPtr = NULL; waitPtr != NULL;
            prevPtr = waitPtr, waitPtr = waitPtr->nextPtr) {
        if ((pid != waitPtr->pid) && (pid != -1)) {
            continue;
        }
        if (!(options & WUNTRACED) && (WIFSTOPPED(waitPtr->status))) {
            continue;
        }
        result = waitPtr->pid;
        *statusPtr = *((int *) &waitPtr->status);
        if (prevPtr == NULL) {
            deadList = waitPtr->nextPtr;
        } else {
            prevPtr->nextPtr = waitPtr->nextPtr;
        }
        ckfree((char *) waitPtr);
        return result;
    }

    /*
     * Wait for any process to stop or exit. If it's an acceptable one then
     * return it to the caller; otherwise store information about it in the
     * list of exited processes and try again. On systems that have only wait
     * but not wait3, there are several situations we can't handle, but we do
     * the best we can (e.g. can still handle some combinations of options by
     * invoking wait instead of wait3).
     */

    while (1) {
#if NO_WAIT3
        if (options & WNOHANG) {
            return 0;
        }
        if (options != 0) {
            errno = EINVAL;
            return -1;
        }
        result = wait(&status);
#else
        result = wait3(&status, options, 0);
#endif
        if ((result == -1) && (errno == EINTR)) {
            continue;
        }
        if (result <= 0) {
            return result;
        }

        if ((pid != result) && (pid != -1)) {
            goto saveInfo;
        }
        if (!(options & WUNTRACED) && (WIFSTOPPED(status))) {
            goto saveInfo;
        }
        *statusPtr = *((int *) &status);
        return result;

        /*
         * Can't return this info to caller. Save it in the list of stopped or
         * exited processes. Tricky point: first check for an existing entry
         * for the process and overwrite it if it exists (e.g. a previously
         * stopped process might now be dead).
         */

    saveInfo:
        for (waitPtr = deadList; waitPtr != NULL; waitPtr = waitPtr->nextPtr) {
            if (waitPtr->pid == result) {
                waitPtr->status = status;
                goto waitAgain;
            }
        }
        waitPtr = (WaitInfo *) ckalloc(sizeof(WaitInfo));
        waitPtr->pid = result;
        waitPtr->status = status;
        waitPtr->nextPtr = deadList;
        deadList = waitPtr;

    waitAgain:
        continue;
    }
}