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Commit 7f0ee023 authored by Keith Randall's avatar Keith Randall
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runtime: revert of CL 8852047: do hashmap grow work during reads. 

seems to break freebsd-386.

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/9915047
parent 07b6add0
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Inline Side-by-side
Showing with 73 additions and 94 deletions
src/pkg/runtime/hashmap.c
View file @ 7f0ee023
......@@ -107,9 +107,6 @@ struct Hmap
uintptr nevacuate; // progress counter for evacuation (buckets less than this have been evacuated)
};
// token to store in nevacuate field when locking the table to evacuate a bucket.
#define EVAC_LOCK ((uintptr)-1)
// possible flags
enum
{
......@@ -117,7 +114,7 @@ enum
IndirectValue = 2, // storing pointers to values
Iterator = 4, // there may be an iterator using buckets
OldIterator = 8, // there may be an iterator using oldbuckets
CanFreeBucket = 16, // ok to free buckets TODO: remove - unused
CanFreeBucket = 16, // ok to free buckets
CanFreeKey = 32, // keys are indirect and ok to free keys
};
......@@ -288,14 +285,12 @@ hash_init(MapType *t, Hmap *h, uint32 hint)
// Moves entries in oldbuckets[i] to buckets[i] and buckets[i+2^k].
// We leave the original bucket intact, except for the evacuated marks, so that
// lookup and iterators can still iterate through the old buckets.
// Multiple threads must not be evacuating the same bucket at the same time.
// iterators can still iterate through the old buckets.
static void
evacuate(MapType *t, Hmap *h, uintptr oldbucket)
{
Bucket *b;
Bucket *nextb;
Bucket *mainb;
Bucket *x, *y;
Bucket *newx, *newy;
uintptr xi, yi;
......@@ -304,14 +299,15 @@ evacuate(MapType *t, Hmap *h, uintptr oldbucket)
uintptr i;
byte *k, *v;
byte *xk, *yk, *xv, *yv;
byte *ob;
mainb = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
newbit = (uintptr)1 << (h->B - 1);
if(evacuated(mainb)) // someone else already evacuated this bucket.
return;
if(!evacuated(b)) {
// TODO: reuse overflow buckets instead of using new ones, if there
// is no iterator using the old buckets. (If CanFreeBuckets and !OldIterator.)
b = mainb;
x = (Bucket*)(h->buckets + oldbucket * h->bucketsize);
y = (Bucket*)(h->buckets + (oldbucket + newbit) * h->bucketsize);
clearbucket(x);
......@@ -383,75 +379,63 @@ evacuate(MapType *t, Hmap *h, uintptr oldbucket)
yv += h->valuesize;
}
}
b = b->overflow;
} while(b != nil);
// Mark main bucket as evacuated. This write commits the
// bucket evacuation (readers can start using the new buckets).
b = mainb->overflow;
runtime·atomicstorep(&mainb->overflow, (Bucket*)((uintptr)b + 1));
// Mark overflow buckets for any iterators.
// These writes don't need to reach anyone until the next hashtable
// modification, so they don't need to be synchronized.
while(b != nil) {
// mark as evacuated so we don't do it again.
// this also tells any iterators that this data isn't golden anymore.
nextb = b->overflow;
b->overflow = (Bucket*)((uintptr)nextb + 1);
b = nextb;
} while(b != nil);
// Free old overflow buckets as much as we can.
if((h->flags & OldIterator) == 0) {
b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
if((h->flags & CanFreeBucket) != 0) {
while((nextb = overflowptr(b)) != nil) {
b->overflow = nextb->overflow;
runtime·free(nextb);
}
} else {
// can't explicitly free overflow buckets, but at least
// we can unlink them.
b->overflow = (Bucket*)1;
}
}
}
// advance evacuation mark
if(oldbucket == h->nevacuate) {
h->nevacuate = oldbucket + 1;
if(oldbucket + 1 == newbit) { // newbit == # of oldbuckets
// free main bucket array
if((h->flags & (OldIterator | CanFreeBucket)) == CanFreeBucket) {
ob = h->oldbuckets;
h->oldbuckets = nil;
runtime·free(ob);
} else {
h->oldbuckets = nil;
}
}
}
if(docheck)
check(t, h);
}
// Ensure that bucket has been evacuated from oldbuckets so that we can modify it.
// Not multithreaded safe - you must not call this from anywhere except hash table
// modifications (where we're guaranteed external synchronization).
static void
grow_work(MapType *t, Hmap *h, uintptr bucket)
{
uintptr noldbuckets;
intptr n;
// evac the bucket we're going to need
noldbuckets = (uintptr)1 << (h->B - 1);
evacuate(t, h, bucket & (noldbuckets - 1));
// evac another bucket to make progress
n = h->nevacuate;
evacuate(t, h, n);
// record what we've done
h->nevacuate = n + 1;
if(n + 1 == noldbuckets)
h->oldbuckets = nil;
}
// Do some work for growing the table.
// Multithreaded-safe.
static void
grow_work_read(MapType *t, Hmap *h) {
uintptr noldbuckets;
intptr n;
noldbuckets = (uintptr)1 << (h->B - 1);
// Get evacuation lock. If we can't get it, fine, that means
// someone else is making progress which is good enough.
n = h->nevacuate;
if(n != EVAC_LOCK && // no one has evac lock
n != noldbuckets && // there's still work to do
runtime·casp((void**)&h->nevacuate, (void*)n, (void*)EVAC_LOCK)) { // we acquired lock
// We're now the exclusive evacuator.
evacuate(t, h, n);
// make sure we evacuate the oldbucket corresponding
// to the bucket we're about to use
evacuate(t, h, bucket & (noldbuckets - 1));
// record that we're done.
runtime·atomicstorep((void**)&h->nevacuate, (void*)(n + 1));
if(n + 1 == noldbuckets) {
// commit finishing of grow.
runtime·atomicstorep(&h->oldbuckets, nil);
// note: can't free oldbuckets, someone might be using it.
// it will have to get GCed.
}
}
// evacuate one more oldbucket to make progress on growing
if(h->oldbuckets != nil)
evacuate(t, h, h->nevacuate);
}
static void
......@@ -496,7 +480,7 @@ hash_lookup(MapType *t, Hmap *h, byte **keyp)
{
void *key;
uintptr hash;
uintptr bucket;
uintptr bucket, oldbucket;
Bucket *b;
uint8 top;
uintptr i;
......@@ -511,14 +495,13 @@ hash_lookup(MapType *t, Hmap *h, byte **keyp)
hash = h->hash0;
t->key->alg->hash(&hash, t->key->size, key);
bucket = hash & (((uintptr)1 << h->B) - 1);
b = runtime·atomicloadp(&h->oldbuckets);
if(b != nil) {
grow_work_read(t, h);
b = (Bucket*)((byte*)b + (bucket & (((uintptr)1 << (h->B - 1)) - 1)) * h->bucketsize);
if(((uintptr)runtime·atomicloadp(&b->overflow) & 1) != 0)
goto newbucket;
if(h->oldbuckets != nil) {
oldbucket = bucket & (((uintptr)1 << (h->B - 1)) - 1);
b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
if(evacuated(b)) {
b = (Bucket*)(h->buckets + bucket * h->bucketsize);
}
} else {
newbucket:
b = (Bucket*)(h->buckets + bucket * h->bucketsize);
}
top = hash >> (sizeof(uintptr)*8 - 8);
......@@ -535,7 +518,7 @@ hash_lookup(MapType *t, Hmap *h, byte **keyp)
}
}
}
b = overflowptr(b);
b = b->overflow;
} while(b != nil);
return nil;
}
......@@ -829,7 +812,6 @@ hash_next(struct hash_iter *it)
uintptr bucket, oldbucket;
uintptr hash;
Bucket *b;
byte *oldbuckets;
uintptr i;
intptr check_bucket;
bool eq;
......@@ -851,15 +833,14 @@ next:
it->value = nil;
return;
}
if(it->B == h->B && (oldbuckets = runtime·atomicloadp(&h->oldbuckets)) != nil) {
if(h->oldbuckets != nil && it->B == h->B) {
// Iterator was started in the middle of a grow, and the grow isn't done yet.
// If the bucket we're looking at hasn't been filled in yet (i.e. the old
// bucket hasn't been evacuated) then we need to iterate through the old
// bucket and only return the ones that will be migrated to this bucket.
grow_work_read(t, h);
oldbucket = bucket & (((uintptr)1 << (it->B - 1)) - 1);
b = (Bucket*)(oldbuckets + oldbucket * h->bucketsize);
if(((uintptr)runtime·atomicloadp(&b->overflow) & 1) == 0) {
b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
if(!evacuated(b)) {
check_bucket = bucket;
} else {
b = (Bucket*)(it->buckets + bucket * h->bucketsize);
......
src/pkg/runtime/hashmap_fast.c
View file @ 7f0ee023
......@@ -17,7 +17,7 @@ void
HASH_LOOKUP1(MapType *t, Hmap *h, KEYTYPE key, byte *value)
{
uintptr hash;
uintptr bucket;
uintptr bucket, oldbucket;
Bucket *b;
uintptr i;
KEYTYPE *k;
......@@ -83,14 +83,13 @@ dohash:
hash = h->hash0;
HASHFUNC(&hash, sizeof(KEYTYPE), &key);
bucket = hash & (((uintptr)1 << h->B) - 1);
b = runtime·atomicloadp(&h->oldbuckets);
if(b != nil) {
grow_work_read(t, h);
b = (Bucket*)((byte*)b + (bucket & (((uintptr)1 << (h->B - 1)) - 1)) * h->bucketsize);
if(((uintptr)runtime·atomicloadp(&b->overflow) & 1) != 0)
goto newbucket;
if(h->oldbuckets != nil) {
oldbucket = bucket & (((uintptr)1 << (h->B - 1)) - 1);
b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
if(evacuated(b)) {
b = (Bucket*)(h->buckets + bucket * h->bucketsize);
}
} else {
newbucket:
b = (Bucket*)(h->buckets + bucket * h->bucketsize);
}
top = hash >> (sizeof(uintptr)*8 - 8);
......@@ -104,7 +103,7 @@ dohash:
return;
}
}
b = overflowptr(b);
b = b->overflow;
} while(b != nil);
}
value = empty_value;
......@@ -116,7 +115,7 @@ void
HASH_LOOKUP2(MapType *t, Hmap *h, KEYTYPE key, byte *value, bool res)
{
uintptr hash;
uintptr bucket;
uintptr bucket, oldbucket;
Bucket *b;
uintptr i;
KEYTYPE *k;
......@@ -188,14 +187,13 @@ dohash:
hash = h->hash0;
HASHFUNC(&hash, sizeof(KEYTYPE), &key);
bucket = hash & (((uintptr)1 << h->B) - 1);
b = runtime·atomicloadp(&h->oldbuckets);
if(b != nil) {
grow_work_read(t, h);
b = (Bucket*)((byte*)b + (bucket & (((uintptr)1 << (h->B - 1)) - 1)) * h->bucketsize);
if(((uintptr)runtime·atomicloadp(&b->overflow) & 1) != 0)
goto newbucket;
if(h->oldbuckets != nil) {
oldbucket = bucket & (((uintptr)1 << (h->B - 1)) - 1);
b = (Bucket*)(h->oldbuckets + oldbucket * h->bucketsize);
if(evacuated(b)) {
b = (Bucket*)(h->buckets + bucket * h->bucketsize);
}
} else {
newbucket:
b = (Bucket*)(h->buckets + bucket * h->bucketsize);
}
top = hash >> (sizeof(uintptr)*8 - 8);
......@@ -211,7 +209,7 @@ dohash:
return;
}
}
b = overflowptr(b);
b = b->overflow;
} while(b != nil);
}
value = empty_value;
......
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