--- ray/src/rt/ambient.c	1993/01/20 10:48:23	2.15
+++ ray/src/rt/ambient.c	1993/08/04 14:22:11	2.19
@@ -35,8 +35,8 @@ double	minarad;		/* minimum ambient radius */
 
 static AMBTREE	atrunk;		/* our ambient trunk node */
 
-static char  *ambfname = NULL;	/* ambient file name */
 static FILE  *ambfp = NULL;	/* ambient file pointer */
+static int  nunflshed = 0;	/* number of unflushed ambient values */
 
 #define	 AMBFLUSH	(BUFSIZ/AMBVALSIZ)
 
@@ -45,7 +45,10 @@ static FILE  *ambfp = NULL;	/* ambient file pointer */
 #define	 newambtree()	(AMBTREE *)calloc(8, sizeof(AMBTREE))
 
 extern long  ftell(), lseek();
-static int  initambfile(), avsave(), avinsert(), ambsync();
+static int  initambfile(), avsave(), avinsert();
+#ifdef  F_SETLKW
+static  aflock();
+#endif
 
 
 setambres(ar)				/* set ambient resolution */
@@ -73,23 +76,25 @@ char  *afile;
 	AMBVAL	amb;
 						/* init ambient limits */
 	setambres(ambres);
+	if (afile == NULL)
+		return;
 						/* open ambient file */
-	if ((ambfname = afile) != NULL)
-		if ((ambfp = fopen(afile, "r+")) != NULL) {
-			initambfile(0);
-			headlen = ftell(ambfp);
-			while (readambval(&amb, ambfp))
-				avinsert(&amb, &atrunk, thescene.cuorg,
-						thescene.cusize);
-							/* align */
-			fseek(ambfp, -((ftell(ambfp)-headlen)%AMBVALSIZ), 1);
-		} else if ((ambfp = fopen(afile, "w+")) != NULL)
-			initambfile(1);
-		else {
-			sprintf(errmsg, "cannot open ambient file \"%s\"",
-					afile);
-			error(SYSTEM, errmsg);
-		}
+	if ((ambfp = fopen(afile, "r+")) != NULL) {
+		initambfile(0);
+		headlen = ftell(ambfp);
+		while (readambval(&amb, ambfp))
+			avinsert(&amb, &atrunk, thescene.cuorg,
+					thescene.cusize);
+						/* align */
+		fseek(ambfp, -((ftell(ambfp)-headlen)%AMBVALSIZ), 1);
+	} else if ((ambfp = fopen(afile, "w+")) != NULL)
+		initambfile(1);
+	else {
+		sprintf(errmsg, "cannot open ambient file \"%s\"", afile);
+		error(SYSTEM, errmsg);
+	}
+	nunflshed++;	/* lie */
+	ambsync();
 }
 
 
@@ -305,6 +310,9 @@ int  creat;
 {
 	extern char  *progname, *octname, VersionID[];
 
+#ifdef	F_SETLKW
+	aflock(creat ? F_WRLCK : F_RDLCK);
+#endif
 #ifdef MSDOS
 	setmode(fileno(ambfp), O_BINARY);
 #endif
@@ -323,7 +331,6 @@ int  creat;
 		putambmagic(ambfp);
 	} else if (checkheader(ambfp, AMBFMT, NULL) < 0 || !hasambmagic(ambfp))
 		error(USER, "bad ambient file");
-	ambsync();
 }
 
 
@@ -331,18 +338,14 @@ static
 avsave(av)				/* insert and save an ambient value */
 AMBVAL	*av;
 {
-	static int  nunflshed = 0;
-
 	avinsert(av, &atrunk, thescene.cuorg, thescene.cusize);
 	if (ambfp == NULL)
 		return;
 	if (writambval(av, ambfp) < 0)
 		goto writerr;
-	if (++nunflshed >= AMBFLUSH) {
+	if (++nunflshed >= AMBFLUSH)
 		if (ambsync() == EOF)
 			goto writerr;
-		nunflshed = 0;
-	}
 	return;
 writerr:
 	error(SYSTEM, "error writing ambient file");
@@ -386,42 +389,43 @@ memerr:
 }
 
 
-#ifdef	NIX
+#ifdef	F_SETLKW
 
 static
-ambsync()			/* flush ambient file */
+aflock(typ)			/* lock/unlock ambient file */
+int  typ;
 {
-	return(fflush(ambfp));
+	static struct flock  fls;	/* static so initialized to zeroes */
+
+	fls.l_type = typ;
+	if (fcntl(fileno(ambfp), F_SETLKW, &fls) < 0)
+		error(SYSTEM, "cannot (un)lock ambient file");
 }
 
-#else
 
-static
+int
 ambsync()			/* synchronize ambient file */
 {
 	static FILE  *ambinp = NULL;
 	static long  lastpos = -1;
-	struct flock  fls;
 	long  flen;
 	AMBVAL	avs;
 	register int  n;
-				/* gain exclusive access */
-	fls.l_type = F_WRLCK;
-	fls.l_whence = 0;
-	fls.l_start = 0L;
-	fls.l_len = 0L;
-	if (fcntl(fileno(ambfp), F_SETLKW, &fls) < 0)
-		error(SYSTEM, "cannot lock ambient file");
-	if (lastpos < 0)	/* initializing */
+
+	if (nunflshed == 0)
+		return(0);
+	if (lastpos < 0)	/* initializing (locked in initambfile) */
 		goto syncend;
+				/* gain exclusive access */
+	aflock(F_WRLCK);
 				/* see if file has grown */
 	if ((flen = lseek(fileno(ambfp), 0L, 2)) < 0)
 		error(SYSTEM, "cannot seek on ambient file");
 	if (n = flen - lastpos) {		/* file has grown */
-		if (ambinp == NULL) {
-			ambinp = fopen(ambfname, "r");
+		if (ambinp == NULL) {		/* use duplicate filedes */
+			ambinp = fdopen(dup(fileno(ambfp)), "r");
 			if (ambinp == NULL)
-				error(SYSTEM, "fopen failed in ambsync");
+				error(SYSTEM, "fdopen failed in ambsync");
 		}
 		if (fseek(ambinp, lastpos, 0) < 0)
 			error(SYSTEM, "fseek failed in ambsync");
@@ -436,9 +440,20 @@ ambsync()			/* synchronize ambient file */
 syncend:
 	n = fflush(ambfp);			/* calls write() at last */
 	lastpos = lseek(fileno(ambfp), 0L, 1);
-	fls.l_type = F_UNLCK;			/* release file */
-	fcntl(fileno(ambfp), F_SETLKW, &fls);
+	aflock(F_UNLCK);			/* release file */
+	nunflshed = 0;
 	return(n);
+}
+
+#else
+
+int
+ambsync()			/* flush ambient file */
+{
+	if (nunflshed == 0)
+		return(0);
+	nunflshed = 0;
+	return(fflush(ambfp));
 }
 
 #endif