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| author | Austin Clements <austin@google.com> | 2016-09-26 13:10:41 -0400 |
|---|---|---|
| committer | Austin Clements <austin@google.com> | 2016-10-03 22:00:06 +0000 |
| commit | bf776a988bf6fe82cbef5cfc954f33d127c5172c (patch) | |
| tree | 2929d956388f87b7d538bd87c3aee26c93700dc1 /src/runtime | |
| parent | 38f1df66ff231458a81cb07e7b147f30854b45d4 (diff) | |
| download | go-bf776a988bf6fe82cbef5cfc954f33d127c5172c.tar.xz | |
runtime: document bmap.tophash
In particular, it wasn't obvious that some values are special (unless
you also found those special values), so document that it isn't
necessarily a hash value.
Change-Id: Iff292822b44408239e26cd882dc07be6df2c1d38
Reviewed-on: https://go-review.googlesource.com/30143
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Diffstat (limited to 'src/runtime')
| -rw-r--r-- | src/runtime/hashmap.go | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/src/runtime/hashmap.go b/src/runtime/hashmap.go index e15926b05a..ab99d24c35 100644 --- a/src/runtime/hashmap.go +++ b/src/runtime/hashmap.go @@ -130,6 +130,9 @@ type hmap struct { // A bucket for a Go map. type bmap struct { + // tophash generally contains the top byte of the hash value + // for each key in this bucket. If tophash[0] < minTopHash, + // tophash[0] is a bucket evacuation state instead. tophash [bucketCnt]uint8 // Followed by bucketCnt keys and then bucketCnt values. // NOTE: packing all the keys together and then all the values together makes the @@ -1079,6 +1082,8 @@ func evacuate(t *maptype, h *hmap, oldbucket uintptr) { // Unlink the overflow buckets & clear key/value to help GC. if h.flags&oldIterator == 0 { b = (*bmap)(add(h.oldbuckets, oldbucket*uintptr(t.bucketsize))) + // Preserve b.tophash because the evacuation + // state is maintained there. memclr(add(unsafe.Pointer(b), dataOffset), uintptr(t.bucketsize)-dataOffset) } } |