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pack.c: limit number of open packfiles.

Git repositories with a lot of pushes or pulls
but few repacks would end up with a lot of open
files. This wasn't a real problem, but it would
cause warnings on the command line.

This change limits the number of concurrent open
packs to 32.

--- a/pack.c

+++ b/pack.c

@@ -50,10 +50,13 @@

 };

 struct Packf {

-	int	refs;

-	Biobuf	*pack;

+	char	path[128];

 	char	*idx;

 	vlong	nidx;

+

+	int	refs;

+	Biobuf	*pack;

+	vlong	opentm;

 };

 static int	readpacked(Biobuf *, Object *, int);

@@ -66,6 +69,7 @@

 int	cachemax = 4096;

 Packf	*packf;

 int	npackf;

+int	openpacks;

 static void

 clear(Object *o)

@@ -169,66 +173,119 @@

 }

 static int

-openpack(Packf *pf, char *name)

+loadpack(Packf *pf, char *name)

 {

 	char buf[128];

-	int ifd;

+	int i, ifd;

 	Dir *d;

 	memset(pf, 0, sizeof(Packf));

-	snprint(buf, sizeof(buf), ".git/objects/pack/%s.pack", name);

-	pf->pack = Bopen(buf, OREAD);

 	snprint(buf, sizeof(buf), ".git/objects/pack/%s.idx", name);

-	ifd = open(buf, OREAD);

-	if(pf->pack == nil || ifd == -1)

-		goto errorf;

+	snprint(pf->path, sizeof(pf->path), ".git/objects/pack/%s.pack", name);

+	/*

+	 * if we already have the pack open, just

+	 * steal the loaded info

+	 */

+	for(i = 0; i < npackf; i++){

+		if(strcmp(pf->path, packf[i].path) == 0){

+			pf->pack = packf[i].pack;

+			pf->idx = packf[i].idx;

+			pf->nidx = packf[i].nidx;

+			packf[i].idx = nil;

+			packf[i].pack = nil;

+		}

+	}

+	if((ifd = open(buf, OREAD)) == -1)

+		goto error;

 	if((d = dirfstat(ifd)) == nil)

-		goto errorf;

+		goto error;

 	pf->nidx = d->length;

 	pf->idx = emalloc(pf->nidx);

-	if(readn(ifd, pf->idx, pf->nidx) != pf->nidx)

-		goto errori;

+	if(readn(ifd, pf->idx, pf->nidx) != pf->nidx){

+		free(pf->idx);

+		free(d);

+		goto error;

+	}

 	free(d);

 	return 0;

-errori:

-	free(d);

-	free(pf->idx);

-errorf:

-	if(pf->pack == nil) Bterm(pf->pack);

-	if(ifd != -1) close(ifd);

-	return -1;		

+error:

+	if(ifd != -1)

+		close(ifd);

+	return -1;	

 }

 static void

 refreshpacks(void)

 {

-	Packf *pf;

-	int i, n, l;

+	Packf *pf, *new;

+	int i, n, l, nnew;

 	Dir *d;

-	for(i = 0; i < npackf; i++){

-		pf = &packf[i];

-		free(pf->idx);

-		Bterm(pf->pack);

-	}

-	free(packf);

 	if((n = slurpdir(".git/objects/pack", &d)) == -1)

 		return;

-

-	npackf = 0;

-	packf = eamalloc(n, sizeof(Packf));

+	nnew = 0;

+	new = eamalloc(n, sizeof(Packf));

 	for(i = 0; i < n; i++){

 		l = strlen(d[i].name);

 		if(l > 4 && strcmp(d[i].name + l - 4, ".idx") != 0)

 			continue;

 		d[i].name[l - 4] = 0;

-		if(openpack(&packf[npackf], d[i].name) != -1)

-			npackf++;

+		if(loadpack(&new[nnew], d[i].name) != -1)

+			nnew++;

 	}

+	for(i = 0; i < npackf; i++){

+		pf = &packf[i];

+		free(pf->idx);

+		if(pf->pack != nil)

+			Bterm(pf->pack);

+	}

+	free(packf);

+	packf = new;

+	npackf = nnew;

 	free(d);

 }

+static Biobuf*

+openpack(Packf *pf)

+{

+	vlong t;

+	int i, best;

+

+	if(pf->pack == nil){

+		if((pf->pack = Bopen(pf->path, OREAD)) == nil)

+			return nil;

+		pf->opentm = nsec();

+		openpacks++;

+	}

+	if(openpacks == Npackcache){

+		t = pf->opentm;

+		best = -1;

+		for(i = 0; i < npackf; i++){

+			if(packf[i].opentm >= t && packf[i].refs > 0){

+				t = packf[i].opentm;

+				best = i;

+			}

+		}

+		if(best != -1){

+			Bterm(packf[best].pack);

+			packf[best].pack = nil;

+			openpacks--;

+		}

+	}

+	pf->refs++;

+	return pf->pack;

+}

+

+static void

+closepack(Packf *pf)

+{

+	if(--pf->refs == 0){

+		Bterm(pf->pack);

+		pf->pack = nil;

+	}

+}

+

 static u32int

 crc32(u32int crc, char *b, int nb)

 {

@@ -898,7 +955,7 @@

 {

 	char path[Pathmax], hbuf[41];

 	Object *obj, *new;

-	int i, retried;

+	int i, r, retried;

 	Biobuf *f;

 	vlong o;

@@ -944,11 +1001,13 @@

 retry:

 	for(i = 0; i < npackf; i++){

 		if((o = searchindex(packf[i].idx, packf[i].nidx, h)) != -1){

-			f = packf[i].pack;

-			if(Bseek(f, o, 0) == -1)

-				goto errorf;

-			if(readpacked(f, obj, flag) == -1)

-				goto errorf;

+			if((f = openpack(&packf[i])) == nil)

+				goto error;

+			if((r = Bseek(f, o, 0)) != -1)

+				r = readpacked(f, obj, flag);

+			closepack(&packf[i]);

+			if(r == -1)

+				goto error;

 			parseobject(obj);

 			cache(obj);

 			return obj;

@@ -974,7 +1033,6 @@

 		refreshpacks();

 		goto retry;

 	}

-

 errorf:

 	Bterm(f);

 error: