plan9port

bwatch.c (6721B)

---

 #include "stdinc.h"
 #include "dat.h"
 #include "fns.h"
 #include "error.h"
 
 /*
  * Lock watcher.  Check that locking of blocks is always down.
  *
  * This is REALLY slow, and it won't work when the blocks aren't
  * arranged in a tree (e.g., after the first snapshot).  But it's great
  * for debugging.
  */
 enum
 {
 	MaxLock = 16,
 	HashSize = 1009,
 };
 
 /*
  * Thread-specific watch state.
  */
 typedef struct WThread WThread;
 struct WThread
 {
 	Block *b[MaxLock];	/* blocks currently held */
 	uint nb;
 	uint pid;
 };
 
 typedef struct WMap WMap;
 typedef struct WEntry WEntry;
 
 struct WEntry
 {
 	uchar c[VtScoreSize];
 	uchar p[VtScoreSize];
 	int off;
 
 	WEntry *cprev;
 	WEntry *cnext;
 	WEntry *pprev;
 	WEntry *pnext;
 };
 
 struct WMap
 {
 	QLock lk;
 
 	WEntry *hchild[HashSize];
 	WEntry *hparent[HashSize];
 };
 
 static WMap map;
 static void **wp;
 static uint blockSize;
 static WEntry *pool;
 uint bwatchDisabled;
 
 static uint
 hash(uchar score[VtScoreSize])
 {
 	uint i, h;
 
 	h = 0;
 	for(i=0; i<VtScoreSize; i++)
 		h = h*37 + score[i];
 	return h%HashSize;
 }
 
 #include <pool.h>
 static void
 freeWEntry(WEntry *e)
 {
 	memset(e, 0, sizeof(WEntry));
 	e->pnext = pool;
 	pool = e;
 }
 
 static WEntry*
 allocWEntry(void)
 {
 	int i;
 	WEntry *w;
 
 	w = pool;
 	if(w == nil){
 		w = vtmallocz(1024*sizeof(WEntry));
 		for(i=0; i<1024; i++)
 			freeWEntry(&w[i]);
 		w = pool;
 	}
 	pool = w->pnext;
 	memset(w, 0, sizeof(WEntry));
 	return w;
 }
 
 /*
  * remove all dependencies with score as a parent
  */
 static void
 _bwatchResetParent(uchar *score)
 {
 	WEntry *w, *next;
 	uint h;
 
 	h = hash(score);
 	for(w=map.hparent[h]; w; w=next){
 		next = w->pnext;
 		if(memcmp(w->p, score, VtScoreSize) == 0){
 			if(w->pnext)
 				w->pnext->pprev = w->pprev;
 			if(w->pprev)
 				w->pprev->pnext = w->pnext;
 			else
 				map.hparent[h] = w->pnext;
 			if(w->cnext)
 				w->cnext->cprev = w->cprev;
 			if(w->cprev)
 				w->cprev->cnext = w->cnext;
 			else
 				map.hchild[hash(w->c)] = w->cnext;
 			freeWEntry(w);
 		}
 	}
 }
 /*
  * and child
  */
 static void
 _bwatchResetChild(uchar *score)
 {
 	WEntry *w, *next;
 	uint h;
 
 	h = hash(score);
 	for(w=map.hchild[h]; w; w=next){
 		next = w->cnext;
 		if(memcmp(w->c, score, VtScoreSize) == 0){
 			if(w->pnext)
 				w->pnext->pprev = w->pprev;
 			if(w->pprev)
 				w->pprev->pnext = w->pnext;
 			else
 				map.hparent[hash(w->p)] = w->pnext;
 			if(w->cnext)
 				w->cnext->cprev = w->cprev;
 			if(w->cprev)
 				w->cprev->cnext = w->cnext;
 			else
 				map.hchild[h] = w->cnext;
 			freeWEntry(w);
 		}
 	}
 }
 
 static uchar*
 parent(uchar c[VtScoreSize], int *off)
 {
 	WEntry *w;
 	uint h;
 
 	h = hash(c);
 	for(w=map.hchild[h]; w; w=w->cnext)
 		if(memcmp(w->c, c, VtScoreSize) == 0){
 			*off = w->off;
 			return w->p;
 		}
 	return nil;
 }
 
 static void
 addChild(uchar p[VtEntrySize], uchar c[VtEntrySize], int off)
 {
 	uint h;
 	WEntry *w;
 
 	w = allocWEntry();
 	memmove(w->p, p, VtScoreSize);
 	memmove(w->c, c, VtScoreSize);
 	w->off = off;
 
 	h = hash(p);
 	w->pnext = map.hparent[h];
 	if(w->pnext)
 		w->pnext->pprev = w;
 	map.hparent[h] = w;
 
 	h = hash(c);
 	w->cnext = map.hchild[h];
 	if(w->cnext)
 		w->cnext->cprev = w;
 	map.hchild[h] = w;
 }
 
 void
 bwatchReset(uchar score[VtScoreSize])
 {
 	qlock(&map.lk);
 	_bwatchResetParent(score);
 	_bwatchResetChild(score);
 	qunlock(&map.lk);
 }
 
 void
 bwatchInit(void)
 {
 	wp = privalloc();
 	*wp = nil;
 }
 
 void
 bwatchSetBlockSize(uint bs)
 {
 	blockSize = bs;
 }
 
 static WThread*
 getWThread(void)
 {
 	WThread *w;
 
 	w = *wp;
 	if(w == nil || w->pid != getpid()){
 		w = vtmallocz(sizeof(WThread));
 		*wp = w;
 		w->pid = getpid();
 	}
 	return w;
 }
 
 /*
  * Derive dependencies from the contents of b.
  */
 void
 bwatchDependency(Block *b)
 {
 	int i, epb, ppb;
 	Entry e;
 
 	if(bwatchDisabled)
 		return;
 
 	qlock(&map.lk);
 	_bwatchResetParent(b->score);
 
 	switch(b->l.type){
 	case BtData:
 		break;
 
 	case BtDir:
 		epb = blockSize / VtEntrySize;
 		for(i=0; i<epb; i++){
 			entryUnpack(&e, b->data, i);
 			if(!(e.flags & VtEntryActive))
 				continue;
 			addChild(b->score, e.score, i);
 		}
 		break;
 
 	default:
 		ppb = blockSize / VtScoreSize;
 		for(i=0; i<ppb; i++)
 			addChild(b->score, b->data+i*VtScoreSize, i);
 		break;
 	}
 	qunlock(&map.lk);
 }
 
 static int
 depth(uchar *s)
 {
 	int d, x;
 
 	d = -1;
 	while(s){
 		d++;
 		s = parent(s, &x);
 	}
 	return d;
 }
 
 static int
 lockConflicts(uchar xhave[VtScoreSize], uchar xwant[VtScoreSize])
 {
 	uchar *have, *want;
 	int havedepth, wantdepth, havepos, wantpos;
 
 	have = xhave;
 	want = xwant;
 
 	havedepth = depth(have);
 	wantdepth = depth(want);
 
 	/*
 	 * walk one or the other up until they're both
  	 * at the same level.
 	 */
 	havepos = -1;
 	wantpos = -1;
 	have = xhave;
 	want = xwant;
 	while(wantdepth > havedepth){
 		wantdepth--;
 		want = parent(want, &wantpos);
 	}
 	while(havedepth > wantdepth){
 		havedepth--;
 		have = parent(have, &havepos);
 	}
 
 	/*
 	 * walk them up simultaneously until we reach
 	 * a common ancestor.
 	 */
 	while(have && want && memcmp(have, want, VtScoreSize) != 0){
 		have = parent(have, &havepos);
 		want = parent(want, &wantpos);
 	}
 
 	/*
 	 * not part of same tree.  happens mainly with
 	 * newly allocated blocks.
 	 */
 	if(!have || !want)
 		return 0;
 
 	/*
 	 * never walked want: means we want to lock
 	 * an ancestor of have.  no no.
 	 */
 	if(wantpos == -1)
 		return 1;
 
 	/*
 	 * never walked have: means we want to lock a
 	 * child of have.  that's okay.
 	 */
 	if(havepos == -1)
 		return 0;
 
 	/*
 	 * walked both: they're from different places in the tree.
 	 * require that the left one be locked before the right one.
 	 * (this is questionable, but it puts a total order on the block tree).
 	 */
 	return havepos < wantpos;
 }
 
 static void
 stop(void)
 {
 	int fd;
 	char buf[32];
 
 	snprint(buf, sizeof buf, "#p/%d/ctl", getpid());
 	fd = open(buf, OWRITE);
 	write(fd, "stop", 4);
 	close(fd);
 }
 
 /*
  * Check whether the calling thread can validly lock b.
  * That is, check that the calling thread doesn't hold
  * locks for any of b's children.
  */
 void
 bwatchLock(Block *b)
 {
 	int i;
 	WThread *w;
 
 	if(bwatchDisabled)
 		return;
 
 	if(b->part != PartData)
 		return;
 
 	qlock(&map.lk);
 	w = getWThread();
 	for(i=0; i<w->nb; i++){
 		if(lockConflicts(w->b[i]->score, b->score)){
 			fprint(2, "%d: have block %V; shouldn't lock %V\n",
 				w->pid, w->b[i]->score, b->score);
 			stop();
 		}
 	}
 	qunlock(&map.lk);
 	if(w->nb >= MaxLock){
 		fprint(2, "%d: too many blocks held\n", w->pid);
 		stop();
 	}else
 		w->b[w->nb++] = b;
 }
 
 /*
  * Note that the calling thread is about to unlock b.
  */
 void
 bwatchUnlock(Block *b)
 {
 	int i;
 	WThread *w;
 
 	if(bwatchDisabled)
 		return;
 
 	if(b->part != PartData)
 		return;
 
 	w = getWThread();
 	for(i=0; i<w->nb; i++)
 		if(w->b[i] == b)
 			break;
 	if(i>=w->nb){
 		fprint(2, "%d: unlock of unlocked block %V\n", w->pid, b->score);
 		stop();
 	}else
 		w->b[i] = w->b[--w->nb];
 }