/*
 * tclProcess.c --
 *
 *	This file implements the "tcl::process" ensemble for subprocess
 *	management as defined by TIP #462.
 *
 * Copyright (c) 2017 Frederic Bonnet.
 *
 * See the file "license.terms" for information on usage and redistribution of
 * this file, and for a DISCLAIMER OF ALL WARRANTIES.
 */

#include "tclInt.h"

/*
 * Autopurge flag. Process-global because of the way Tcl manages child
 * processes (see tclPipe.c).
 */

static int autopurge = 1;	/* Autopurge flag. */

/*
 * Hash tables that keeps track of all child process statuses. Keys are the
 * child process ids and resolved pids, values are (ProcessInfo *).
 */

typedef struct ProcessInfo {
    Tcl_Pid pid;		/* Process id. */
    int resolvedPid;		/* Resolved process id. */
    int purge;			/* Purge eventualy. */
    TclProcessWaitStatus status;/* Process status. */
    int code;			/* Error code, exit status or signal
				   number. */
    Tcl_Obj *msg;		/* Error message. */
    Tcl_Obj *error;		/* Error code. */
} ProcessInfo;
static Tcl_HashTable infoTablePerPid;
static Tcl_HashTable infoTablePerResolvedPid;
static int infoTablesInitialized = 0;	/* 0 means not yet initialized. */
TCL_DECLARE_MUTEX(infoTablesMutex)

 /*
 * Prototypes for functions defined later in this file:
 */

static void		InitProcessInfo(ProcessInfo *info, Tcl_Pid pid,
			    int resolvedPid);
static void		FreeProcessInfo(ProcessInfo *info);
static int		RefreshProcessInfo(ProcessInfo *info, int options);
static TclProcessWaitStatus WaitProcessStatus(Tcl_Pid pid, int resolvedPid,
			    int options, int *codePtr, Tcl_Obj **msgPtr,
			    Tcl_Obj **errorObjPtr);
static Tcl_Obj *	BuildProcessStatusObj(ProcessInfo *info);
static int		ProcessListObjCmd(ClientData clientData,
			    Tcl_Interp *interp, int objc,
			    Tcl_Obj *const objv[]);
static int		ProcessStatusObjCmd(ClientData clientData,
			    Tcl_Interp *interp, int objc,
			    Tcl_Obj *const objv[]);
static int		ProcessPurgeObjCmd(ClientData clientData,
			    Tcl_Interp *interp, int objc,
			    Tcl_Obj *const objv[]);
static int		ProcessAutopurgeObjCmd(ClientData clientData,
			    Tcl_Interp *interp, int objc,
			    Tcl_Obj *const objv[]);

/*
 *----------------------------------------------------------------------
 *
 * InitProcessInfo --
 *
 *	Initializes the ProcessInfo structure.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Memory written.
 *
 *----------------------------------------------------------------------
 */

void
InitProcessInfo(
    ProcessInfo *info,		/* Structure to initialize. */
    Tcl_Pid pid,		/* Process id. */
    int resolvedPid)		/* Resolved process id. */
{
    info->pid = pid;
    info->resolvedPid = resolvedPid;
    info->purge = 0;
    info->status = TCL_PROCESS_UNCHANGED;
    info->code = 0;
    info->msg = NULL;
    info->error = NULL;
}

/*
 *----------------------------------------------------------------------
 *
 * FreeProcessInfo --
 *
 *	Free the ProcessInfo structure.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Memory deallocated, Tcl_Obj refcount decreased.
 *
 *----------------------------------------------------------------------
 */

void
FreeProcessInfo(
    ProcessInfo *info)		/* Structure to free. */
{
    /*
     * Free stored Tcl_Objs.
     */

    if (info->msg) {
	Tcl_DecrRefCount(info->msg);
    }
    if (info->error) {
	Tcl_DecrRefCount(info->error);
    }

    /*
     * Free allocated structure.
     */

    ckfree(info);
}

/*
 *----------------------------------------------------------------------
 *
 * RefreshProcessInfo --
 *
 *	Refresh process info.
 *
 * Results:
 *	Nonzero if state changed, else zero.
 *
 * Side effects:
 *	May call WaitProcessStatus, which can block if WNOHANG option is set.
 *
 *----------------------------------------------------------------------
 */

int
RefreshProcessInfo(
    ProcessInfo *info,		/* Structure to refresh. */
    int options			/* Options passed to WaitProcessStatus. */
)
{
    if (info->status == TCL_PROCESS_UNCHANGED) {
	/*
	 * Refresh & store status.
	 */

	info->status = WaitProcessStatus(info->pid, info->resolvedPid,
		options, &info->code, &info->msg, &info->error);
	if (info->msg) Tcl_IncrRefCount(info->msg);
	if (info->error) Tcl_IncrRefCount(info->error);
	return (info->status != TCL_PROCESS_UNCHANGED);
    } else {
	/*
	 * No change.
	 */

	return 0;
    }
}

/*
 *----------------------------------------------------------------------
 *
 * WaitProcessStatus --
 *
 *	Wait for process status to change.
 *
 * Results:
 *	TclProcessWaitStatus enum value.
 *
 * Side effects:
 *	May call WaitProcessStatus, which can block if WNOHANG option is set.
 *
 *----------------------------------------------------------------------
 */

TclProcessWaitStatus
WaitProcessStatus(
    Tcl_Pid pid,		/* Process id. */
    int resolvedPid,		/* Resolved process id. */
    int options,		/* Options passed to Tcl_WaitPid. */
    int *codePtr,		/* If non-NULL, will receive either:
				 *  - 0 for normal exit.
				 *  - errno in case of error.
				 *  - non-zero exit code for abormal exit.
				 *  - signal number if killed or suspended.
				 *  - Tcl_WaitPid status in all other cases.
				 */
    Tcl_Obj **msgObjPtr,	/* If non-NULL, will receive error message. */
    Tcl_Obj **errorObjPtr)	/* If non-NULL, will receive error code. */
{
    int waitStatus;
    Tcl_Obj *errorStrings[5];
    const char *msg;

    pid = Tcl_WaitPid(pid, &waitStatus, options);
    if (pid == 0) {
	/*
	 * No change.
	 */

	return TCL_PROCESS_UNCHANGED;
    }

    /*
     * Get process status.
     */

    if (pid == (Tcl_Pid) -1) {
	/*
	 * POSIX errName msg
	 */

	msg = Tcl_ErrnoMsg(errno);
	if (errno == ECHILD) {
	    /*
	     * This changeup in message suggested by Mark Diekhans to
	     * remind people that ECHILD errors can occur on some
	     * systems if SIGCHLD isn't in its default state.
	     */

	    msg = "child process lost (is SIGCHLD ignored or trapped?)";
	}
	if (codePtr) *codePtr = errno;
	if (msgObjPtr) *msgObjPtr = Tcl_ObjPrintf(
		"error waiting for process to exit: %s", msg);
	if (errorObjPtr) {
	    errorStrings[0] = Tcl_NewStringObj("POSIX", -1);
	    errorStrings[1] = Tcl_NewStringObj(Tcl_ErrnoId(), -1);
	    errorStrings[2] = Tcl_NewStringObj(msg, -1);
	    *errorObjPtr = Tcl_NewListObj(3, errorStrings);
	}
	return TCL_PROCESS_ERROR;
    } else if (WIFEXITED(waitStatus)) {
	if (codePtr) *codePtr = WEXITSTATUS(waitStatus);
	if (!WEXITSTATUS(waitStatus)) {
	    /*
	     * Normal exit.
	     */

	    if (msgObjPtr) *msgObjPtr = NULL;
	    if (errorObjPtr) *errorObjPtr = NULL;
	} else {
	    /*
	     * CHILDSTATUS pid code
	     *
	     * Child exited with a non-zero exit status.
	     */

	    if (msgObjPtr) *msgObjPtr = Tcl_NewStringObj(
		    "child process exited abnormally", -1);
	    if (errorObjPtr) {
		errorStrings[0] = Tcl_NewStringObj("CHILDSTATUS", -1);
		errorStrings[1] = Tcl_NewIntObj(resolvedPid);
		errorStrings[2] = Tcl_NewIntObj(WEXITSTATUS(waitStatus));
		*errorObjPtr = Tcl_NewListObj(3, errorStrings);
	    }
	}
	return TCL_PROCESS_EXITED;
    } else if (WIFSIGNALED(waitStatus)) {
	/*
	 * CHILDKILLED pid sigName msg
	 *
	 * Child killed because of a signal.
	 */

	msg = Tcl_SignalMsg(WTERMSIG(waitStatus));
	if (codePtr) *codePtr = WTERMSIG(waitStatus);
	if (msgObjPtr) *msgObjPtr = Tcl_ObjPrintf(
		"child killed: %s", msg);
	if (errorObjPtr) {
	    errorStrings[0] = Tcl_NewStringObj("CHILDKILLED", -1);
	    errorStrings[1] = Tcl_NewIntObj(resolvedPid);
	    errorStrings[2] = Tcl_NewStringObj(Tcl_SignalId(WTERMSIG(waitStatus)), -1);
	    errorStrings[3] = Tcl_NewStringObj(msg, -1);
	    *errorObjPtr = Tcl_NewListObj(4, errorStrings);
	}
	return TCL_PROCESS_SIGNALED;
    } else if (WIFSTOPPED(waitStatus)) {
	/*
	 * CHILDSUSP pid sigName msg
	 *
	 * Child suspended because of a signal.
	 */

	msg = Tcl_SignalMsg(WSTOPSIG(waitStatus));
	if (codePtr) *codePtr = WSTOPSIG(waitStatus);
	if (msgObjPtr) *msgObjPtr = Tcl_ObjPrintf(
		"child suspended: %s", msg);
	if (errorObjPtr) {
	    errorStrings[0] = Tcl_NewStringObj("CHILDSUSP", -1);
	    errorStrings[1] = Tcl_NewIntObj(resolvedPid);
	    errorStrings[2] = Tcl_NewStringObj(Tcl_SignalId(WSTOPSIG(waitStatus)), -1);
	    errorStrings[3] = Tcl_NewStringObj(msg, -1);
	    *errorObjPtr = Tcl_NewListObj(4, errorStrings);
	}
	return TCL_PROCESS_STOPPED;
    } else {
	/*
	 * TCL OPERATION EXEC ODDWAITRESULT
	 *
	 * Child wait status didn't make sense.
	 */

	if (codePtr) *codePtr = waitStatus;
	if (msgObjPtr) *msgObjPtr = Tcl_NewStringObj(
		"child wait status didn't make sense\n", -1);
	if (errorObjPtr) {
	    errorStrings[0] = Tcl_NewStringObj("TCL", -1);
	    errorStrings[1] = Tcl_NewStringObj("OPERATION", -1);
	    errorStrings[2] = Tcl_NewStringObj("EXEC", -1);
	    errorStrings[3] = Tcl_NewStringObj("ODDWAITRESULT", -1);
	    errorStrings[4] = Tcl_NewIntObj(resolvedPid);
	    *errorObjPtr = Tcl_NewListObj(5, errorStrings);
	}
	return TCL_PROCESS_UNKNOWN_STATUS;
    }
}


/*
 *----------------------------------------------------------------------
 *
 * BuildProcessStatusObj --
 *
 *	Build a list object with process status. The first element is always
 *	a standard Tcl return value, which can be either TCL_OK or TCL_ERROR.
 *	In the latter case, the second element is the error message and the
 *	third element is a Tcl error code (see tclvars).
 *
 * Results:
 *	A list object.
 *
 * Side effects:
 *	Tcl_Objs are created.
 *
 *----------------------------------------------------------------------
 */

Tcl_Obj *
BuildProcessStatusObj(
    ProcessInfo *info)
{
    Tcl_Obj *resultObjs[3];

    if (info->status == TCL_PROCESS_UNCHANGED) {
	/*
	 * Process still running, return empty obj.
	 */

	return Tcl_NewObj();
    }
    if (info->status == TCL_PROCESS_EXITED && info->code == 0) {
	/*
	 * Normal exit, return TCL_OK.
	 */

	return Tcl_NewIntObj(TCL_OK);
    }

    /*
     * Abnormal exit, return {TCL_ERROR msg error}
     */

    resultObjs[0] = Tcl_NewIntObj(TCL_ERROR);
    resultObjs[1] = info->msg;
    resultObjs[2] = info->error;
    return Tcl_NewListObj(3, resultObjs);
}

/*----------------------------------------------------------------------
 *
 * ProcessListObjCmd --
 *
 *	This function implements the 'tcl::process list' Tcl command.
 *	Refer to the user documentation for details on what it does.
 *
 * Results:
 *	Returns a standard Tcl result.
 *
 * Side effects:
 *	Access to the internal structures is protected by infoTablesMutex.
 *
 *----------------------------------------------------------------------
 */

static int
ProcessListObjCmd(
    ClientData clientData,	/* Not used. */
    Tcl_Interp *interp,		/* Current interpreter. */
    int objc,			/* Number of arguments. */
    Tcl_Obj *const objv[])	/* Argument objects. */
{
    Tcl_Obj *list;
    Tcl_HashEntry *entry;
    Tcl_HashSearch search;
    ProcessInfo *info;

    if (objc != 1) {
	Tcl_WrongNumArgs(interp, 1, objv, NULL);
	return TCL_ERROR;
    }

    /*
     * Return the list of all chid process ids.
     */

    list = Tcl_NewListObj(0, NULL);
    Tcl_MutexLock(&infoTablesMutex);
    for (entry = Tcl_FirstHashEntry(&infoTablePerResolvedPid, &search);
	    entry != NULL; entry = Tcl_NextHashEntry(&search)) {
	info = (ProcessInfo *) Tcl_GetHashValue(entry);
	Tcl_ListObjAppendElement(interp, list,
		Tcl_NewIntObj(info->resolvedPid));
    }
    Tcl_MutexUnlock(&infoTablesMutex);
    Tcl_SetObjResult(interp, list);
    return TCL_OK;
}

/*----------------------------------------------------------------------
 *
 * ProcessStatusObjCmd --
 *
 *	This function implements the 'tcl::process status' Tcl command.
 *	Refer to the user documentation for details on what it does.
 *
 * Results:
 *	Returns a standard Tcl result.
 *
 * Side effects:
 *	Access to the internal structures is protected by infoTablesMutex.
 *	Calls RefreshProcessInfo, which can block if -wait switch is given.
 *
 *----------------------------------------------------------------------
 */

static int
ProcessStatusObjCmd(
    ClientData clientData,	/* Not used. */
    Tcl_Interp *interp,		/* Current interpreter. */
    int objc,			/* Number of arguments. */
    Tcl_Obj *const objv[])	/* Argument objects. */
{
    Tcl_Obj *dict;
    int index, options = WNOHANG;
    Tcl_HashEntry *entry;
    Tcl_HashSearch search;
    ProcessInfo *info;
    int numPids;
    Tcl_Obj **pidObjs;
    int result;
    int i;
    int pid;
    Tcl_Obj *const *savedobjv = objv;
    static const char *const switches[] = {
	"-wait", "--", NULL
    };
    enum switches {
	STATUS_WAIT, STATUS_LAST
    };

    while (objc > 1) {
	if (TclGetString(objv[1])[0] != '-') {
	    break;
	}
	if (Tcl_GetIndexFromObj(interp, objv[1], switches, "switches", 0,
		&index) != TCL_OK) {
	    return TCL_ERROR;
	}
	++objv; --objc;
	if (STATUS_WAIT == (enum switches) index) {
	    options = 0;
	} else {
	    break;
	}
    }

    if (objc != 1 && objc != 2) {
	Tcl_WrongNumArgs(interp, 1, savedobjv, "?switches? ?pids?");
	return TCL_ERROR;
    }

    if (objc == 1) {
	/*
	* Return a dict with all child process statuses.
	*/

	dict = Tcl_NewDictObj();
	Tcl_MutexLock(&infoTablesMutex);
	for (entry = Tcl_FirstHashEntry(&infoTablePerResolvedPid, &search);
		entry != NULL; entry = Tcl_NextHashEntry(&search)) {
	    info = (ProcessInfo *) Tcl_GetHashValue(entry);
	    RefreshProcessInfo(info, options);

	    if (info->purge && autopurge) {
		/*
		 * Purge entry.
		 */

		Tcl_DeleteHashEntry(entry);
		entry = Tcl_FindHashEntry(&infoTablePerPid, info->pid);
		Tcl_DeleteHashEntry(entry);
		FreeProcessInfo(info);
	    } else {
		/*
		 * Add to result.
		 */

		Tcl_DictObjPut(interp, dict, Tcl_NewIntObj(info->resolvedPid),
			BuildProcessStatusObj(info));
	    }
	}
	Tcl_MutexUnlock(&infoTablesMutex);
    } else {
	/*
	 * Only return statuses of provided processes.
	 */

	result = Tcl_ListObjGetElements(interp, objv[1], &numPids, &pidObjs);
	if (result != TCL_OK) {
	    return result;
	}
	dict = Tcl_NewDictObj();
	Tcl_MutexLock(&infoTablesMutex);
	for (i = 0; i < numPids; i++) {
	    result = Tcl_GetIntFromObj(interp, pidObjs[i], (int *) &pid);
	    if (result != TCL_OK) {
		Tcl_MutexUnlock(&infoTablesMutex);
		Tcl_DecrRefCount(dict);
		return result;
	    }

	    entry = Tcl_FindHashEntry(&infoTablePerResolvedPid, INT2PTR(pid));
	    if (!entry) {
		/*
		 * Skip unknown process.
		 */

		continue;
	    }

	    info = (ProcessInfo *) Tcl_GetHashValue(entry);
	    RefreshProcessInfo(info, options);

	    if (info->purge && autopurge) {
		/*
		 * Purge entry.
		 */

		Tcl_DeleteHashEntry(entry);
		entry = Tcl_FindHashEntry(&infoTablePerPid, info->pid);
		Tcl_DeleteHashEntry(entry);
		FreeProcessInfo(info);
	    } else {
		/*
		 * Add to result.
		 */

		Tcl_DictObjPut(interp, dict, Tcl_NewIntObj(info->resolvedPid),
			BuildProcessStatusObj(info));
	    }
	}
	Tcl_MutexUnlock(&infoTablesMutex);
    }
    Tcl_SetObjResult(interp, dict);
    return TCL_OK;
}

/*----------------------------------------------------------------------
 *
 * ProcessPurgeObjCmd --
 *
 *	This function implements the 'tcl::process purge' Tcl command.
 *	Refer to the user documentation for details on what it does.
 *
 * Results:
 *	Returns a standard Tcl result.
 *
 * Side effects:
 *	Frees all ProcessInfo structures with their purge flag set.
 *
 *----------------------------------------------------------------------
 */

static int
ProcessPurgeObjCmd(
    ClientData clientData,	/* Not used. */
    Tcl_Interp *interp,		/* Current interpreter. */
    int objc,			/* Number of arguments. */
    Tcl_Obj *const objv[])	/* Argument objects. */
{
    Tcl_HashEntry *entry;
    Tcl_HashSearch search;
    ProcessInfo *info;
    int numPids;
    Tcl_Obj **pidObjs;
    int result;
    int i;
    int pid;

    if (objc != 1 && objc != 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "?pids?");
	return TCL_ERROR;
    }

    /*
     * First reap detached procs so that their purge flag is up-to-date.
     */

    Tcl_ReapDetachedProcs();

    if (objc == 1) {
	/*
	 * Purge all terminated processes.
	 */

	Tcl_MutexLock(&infoTablesMutex);
	for (entry = Tcl_FirstHashEntry(&infoTablePerResolvedPid, &search);
		entry != NULL; entry = Tcl_NextHashEntry(&search)) {
	    info = (ProcessInfo *) Tcl_GetHashValue(entry);
	    if (info->purge) {
		Tcl_DeleteHashEntry(entry);
		entry = Tcl_FindHashEntry(&infoTablePerPid, info->pid);
		Tcl_DeleteHashEntry(entry);
		FreeProcessInfo(info);
	    }
	}
	Tcl_MutexUnlock(&infoTablesMutex);
    } else {
	/*
	 * Purge only provided processes.
	 */

	result = Tcl_ListObjGetElements(interp, objv[1], &numPids, &pidObjs);
	if (result != TCL_OK) {
	    return result;
	}
	Tcl_MutexLock(&infoTablesMutex);
	for (i = 0; i < numPids; i++) {
	    result = Tcl_GetIntFromObj(interp, pidObjs[i], (int *) &pid);
	    if (result != TCL_OK) {
		Tcl_MutexUnlock(&infoTablesMutex);
		return result;
	    }

	    entry = Tcl_FindHashEntry(&infoTablePerResolvedPid, INT2PTR(pid));
	    if (!entry) {
		/*
		 * Skip unknown process.
		 */

		continue;
	    }

	    info = (ProcessInfo *) Tcl_GetHashValue(entry);
	    if (info->purge) {
		Tcl_DeleteHashEntry(entry);
		entry = Tcl_FindHashEntry(&infoTablePerPid, info->pid);
		Tcl_DeleteHashEntry(entry);
		FreeProcessInfo(info);
	    }
	}
	Tcl_MutexUnlock(&infoTablesMutex);
    }

    return TCL_OK;
}

/*----------------------------------------------------------------------
 *
 * ProcessAutopurgeObjCmd --
 *
 *	This function implements the 'tcl::process autopurge' Tcl command.
 *	Refer to the user documentation for details on what it does.
 *
 * Results:
 *	Returns a standard Tcl result.
 *
 * Side effects:
 *	Alters detached process handling by Tcl_ReapDetachedProcs().
 *
 *----------------------------------------------------------------------
 */

static int
ProcessAutopurgeObjCmd(
    ClientData clientData,	/* Not used. */
    Tcl_Interp *interp,		/* Current interpreter. */
    int objc,			/* Number of arguments. */
    Tcl_Obj *const objv[])	/* Argument objects. */
{
    if (objc != 1 && objc != 2) {
	Tcl_WrongNumArgs(interp, 1, objv, "?flag?");
	return TCL_ERROR;
    }

    if (objc == 2) {
	/*
	 * Set given value.
	 */

	int flag;
	int result = Tcl_GetBooleanFromObj(interp, objv[1], &flag);
	if (result != TCL_OK) {
	    return result;
	}

	autopurge = !!flag;
    }

    /*
     * Return current value.
     */

    Tcl_SetObjResult(interp, Tcl_NewBooleanObj(autopurge));
    return TCL_OK;
}

/*
 *----------------------------------------------------------------------
 *
 * TclInitProcessCmd --
 *
 *	This procedure creates the "tcl::process" Tcl command. See the user
 *	documentation for details on what it does.
 *
 * Results:
 *	A standard Tcl result.
 *
 * Side effects:
 *	See the user documentation.
 *
 *----------------------------------------------------------------------
 */

Tcl_Command
TclInitProcessCmd(
    Tcl_Interp *interp)		/* Current interpreter. */
{
    static const EnsembleImplMap processImplMap[] = {
	{"list", ProcessListObjCmd, TclCompileBasic0ArgCmd, NULL, NULL, 1},
	{"status", ProcessStatusObjCmd, TclCompileBasicMin0ArgCmd, NULL, NULL, 1},
	{"purge", ProcessPurgeObjCmd, TclCompileBasic0Or1ArgCmd, NULL, NULL, 1},
	{"autopurge", ProcessAutopurgeObjCmd, TclCompileBasic0Or1ArgCmd, NULL, NULL, 1},
	{NULL, NULL, NULL, NULL, NULL, 0}
    };
    Tcl_Command processCmd;

    if (infoTablesInitialized == 0) {
	Tcl_MutexLock(&infoTablesMutex);
	if (infoTablesInitialized == 0) {
	    Tcl_InitHashTable(&infoTablePerPid, TCL_ONE_WORD_KEYS);
	    Tcl_InitHashTable(&infoTablePerResolvedPid, TCL_ONE_WORD_KEYS);
	    infoTablesInitialized = 1;
	}
	Tcl_MutexUnlock(&infoTablesMutex);
    }

    processCmd = TclMakeEnsemble(interp, "::tcl::process", processImplMap);
    Tcl_Export(interp, Tcl_FindNamespace(interp, "::tcl", NULL, 0),
	    "process", 0);
    return processCmd;
}

/*
 *----------------------------------------------------------------------
 *
 * TclProcessCreated --
 *
 *	Called when a child process has been created by Tcl.
 *
 * Results:
 *	None.
 *
 * Side effects:
 *	Internal structures are updated with a new ProcessInfo.
 *
 *----------------------------------------------------------------------
 */

void
TclProcessCreated(
    Tcl_Pid pid)		/* Process id. */
{
    int resolvedPid;
    Tcl_HashEntry *entry, *entry2;
    int isNew;
    ProcessInfo *info;

    /*
     * Get resolved pid first.
     */

    resolvedPid = TclpGetPid(pid);

    Tcl_MutexLock(&infoTablesMutex);

    /*
     * Create entry in pid table.
     */

    entry = Tcl_CreateHashEntry(&infoTablePerPid, pid, &isNew);
    if (!isNew) {
	/*
	 * Pid was reused, free old info and reuse structure.
	 */

	info = (ProcessInfo *) Tcl_GetHashValue(entry);
	entry2 = Tcl_FindHashEntry(&infoTablePerResolvedPid,
		INT2PTR(resolvedPid));
	if (entry2) Tcl_DeleteHashEntry(entry2);
	FreeProcessInfo(info);
    }

    /*
     * Allocate and initialize info structure.
     */

    info = (ProcessInfo *) ckalloc(sizeof(ProcessInfo));
    InitProcessInfo(info, pid, resolvedPid);

    /*
     * Add entry to tables.
     */

    Tcl_SetHashValue(entry, info);
    entry = Tcl_CreateHashEntry(&infoTablePerResolvedPid, INT2PTR(resolvedPid),
	    &isNew);
    Tcl_SetHashValue(entry, info);

    Tcl_MutexUnlock(&infoTablesMutex);
}

/*
 *----------------------------------------------------------------------
 *
 * TclProcessWait --
 *
 *	Wait for process status to change.
 *
 * Results:
 *	TclProcessWaitStatus enum value.
 *
 * Side effects:
 *	Completed process info structures are purged immediately (autopurge on)
 *	or eventually (autopurge off).
 *
 *----------------------------------------------------------------------
 */

TclProcessWaitStatus
TclProcessWait(
    Tcl_Pid pid,		/* Process id. */
    int options,		/* Options passed to WaitProcessStatus. */
    int *codePtr,		/* If non-NULL, will receive either:
				 *  - 0 for normal exit.
				 *  - errno in case of error.
				 *  - non-zero exit code for abormal exit.
				 *  - signal number if killed or suspended.
				 *  - Tcl_WaitPid status in all other cases.
				 */
    Tcl_Obj **msgObjPtr,	/* If non-NULL, will receive error message. */
    Tcl_Obj **errorObjPtr)	/* If non-NULL, will receive error code. */
{
    Tcl_HashEntry *entry;
    ProcessInfo *info;
    TclProcessWaitStatus result;

    /*
     * First search for pid in table.
     */

    Tcl_MutexLock(&infoTablesMutex);
    entry = Tcl_FindHashEntry(&infoTablePerPid, pid);
    if (!entry) {
	/*
	 * Unknown process, just call WaitProcessStatus and return.
	 */

	result = WaitProcessStatus(pid, TclpGetPid(pid), options, codePtr,
		msgObjPtr, errorObjPtr);
	if (msgObjPtr && *msgObjPtr) Tcl_IncrRefCount(*msgObjPtr);
	if (errorObjPtr && *errorObjPtr) Tcl_IncrRefCount(*errorObjPtr);
    Tcl_MutexUnlock(&infoTablesMutex);
	return result;
    }

    info = (ProcessInfo *) Tcl_GetHashValue(entry);
    if (info->purge) {
	/*
	 * Process has completed but TclProcessWait has already been called,
	 * so report no change.
	 */
    Tcl_MutexUnlock(&infoTablesMutex);

	return TCL_PROCESS_UNCHANGED;
    }

    RefreshProcessInfo(info, options);
    if (info->status == TCL_PROCESS_UNCHANGED) {
	/*
	 * No change, stop there.
	 */
    Tcl_MutexUnlock(&infoTablesMutex);

	return TCL_PROCESS_UNCHANGED;
    }

    /*
     * Set return values.
     */

    result = info->status;
    if (codePtr) *codePtr = info->code;
    if (msgObjPtr) *msgObjPtr = info->msg;
    if (errorObjPtr) *errorObjPtr = info->error;
    if (msgObjPtr && *msgObjPtr) Tcl_IncrRefCount(*msgObjPtr);
    if (errorObjPtr && *errorObjPtr) Tcl_IncrRefCount(*errorObjPtr);

    if (autopurge) {
	/*
	 * Purge now.
	 */

	Tcl_DeleteHashEntry(entry);
	entry = Tcl_FindHashEntry(&infoTablePerResolvedPid,
		INT2PTR(info->resolvedPid));
	Tcl_DeleteHashEntry(entry);
	FreeProcessInfo(info);
    } else {
	/*
	 * Eventually purge. Subsequent calls will return
	 * TCL_PROCESS_UNCHANGED.
	 */

	info->purge = 1;
    }
    Tcl_MutexUnlock(&infoTablesMutex);
    return result;
}