diff --git a/src/runtime/map.go b/src/runtime/map.go index 273e315ea0..9c3a7e2b8c 100644 --- a/src/runtime/map.go +++ b/src/runtime/map.go @@ -1008,6 +1008,22 @@ func mapclear(t *maptype, h *hmap) { h.flags ^= hashWriting + // Mark buckets empty, so existing iterators can be terminated, see issue #59411. + markBucketsEmpty := func(bucket unsafe.Pointer, mask uintptr) { + for i := uintptr(0); i <= mask; i++ { + b := (*bmap)(add(bucket, i*uintptr(t.bucketsize))) + for ; b != nil; b = b.overflow(t) { + for i := uintptr(0); i < bucketCnt; i++ { + b.tophash[i] = emptyRest + } + } + } + } + markBucketsEmpty(h.buckets, bucketMask(h.B)) + if oldBuckets := h.oldbuckets; oldBuckets != nil { + markBucketsEmpty(oldBuckets, h.oldbucketmask()) + } + h.flags &^= sameSizeGrow h.oldbuckets = nil h.nevacuate = 0 diff --git a/test/fixedbugs/issue59411.go b/test/fixedbugs/issue59411.go new file mode 100644 index 0000000000..fc35c9801d --- /dev/null +++ b/test/fixedbugs/issue59411.go @@ -0,0 +1,77 @@ +// run + +// Copyright 2023 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package main + +import ( + "math" + "reflect" +) + +func main() { + for i := 0; i < 100; i++ { + f() + g() + } +} + +func f() { + // Allocate map. + m := map[float64]int{} + // Fill to just before a growth trigger. + const N = 13 << 4 // 6.5 * 2 * 2^k + for i := 0; i < N; i++ { + m[math.NaN()] = i + } + // Trigger growth. + m[math.NaN()] = N + + // Iterate through map. + i := 0 + for range m { + if i == 6 { + // Partway through iteration, clear the map. + clear(m) + } else if i > 6 { + // If we advance to the next iteration, that's a bug. + panic("BAD") + } + i++ + } + if len(m) != 0 { + panic("clear did not empty the map") + } +} + +func g() { + // Allocate map. + m := map[float64]int{} + // Fill to just before a growth trigger. + const N = 13 << 4 // 6.5 * 2 * 2^k + for i := 0; i < N; i++ { + m[math.NaN()] = i + } + // Trigger growth. + m[math.NaN()] = N + + // Iterate through map. + i := 0 + v := reflect.ValueOf(m) + iter := v.MapRange() + for iter.Next() { + if i == 6 { + // Partway through iteration, clear the map. + v.Clear() + } else if i > 6 { + // If we advance to the next iteration, that's a bug. + panic("BAD") + } + i++ + } + if v.Len() != 0 { + panic("clear did not empty the map") + } +}