issue69110.go

     1  // run
     2  
     3  // Copyright 2024 The Go Authors. All rights reserved.
     4  // Use of this source code is governed by a BSD-style
     5  // license that can be found in the LICENSE file.
     6  
     7  package main
     8  
     9  import (
    10  	"maps"
    11  	_ "unsafe"
    12  )
    13  
    14  func main() {
    15  	for i := 0; i < 100; i++ {
    16  		f()
    17  	}
    18  }
    19  
    20  const NB = 4
    21  
    22  func f() {
    23  	// Make a map with NB buckets, at max capacity.
    24  	// 6.5 entries/bucket.
    25  	ne := NB * 13 / 2
    26  	m := map[int]int{}
    27  	for i := 0; i < ne; i++ {
    28  		m[i] = i
    29  	}
    30  
    31  	// delete/insert a lot, to hopefully get lots of overflow buckets
    32  	// and trigger a same-size grow.
    33  	ssg := false
    34  	for i := ne; i < ne+1000; i++ {
    35  		delete(m, i-ne)
    36  		m[i] = i
    37  		if sameSizeGrow(m) {
    38  			ssg = true
    39  			break
    40  		}
    41  	}
    42  	if !ssg {
    43  		return
    44  	}
    45  
    46  	// Insert 1 more entry, which would ordinarily trigger a growth.
    47  	// We can't grow while growing, so we instead go over our
    48  	// target capacity.
    49  	m[-1] = -1
    50  
    51  	// Cloning in this state will make a map with a destination bucket
    52  	// array twice the size of the source.
    53  	_ = maps.Clone(m)
    54  }
    55  
    56  //go:linkname sameSizeGrow runtime.sameSizeGrowForIssue69110Test
    57  func sameSizeGrow(m map[int]int) bool
    58
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