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// 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.
//go:build goexperiment.exectracer2
// Simple not-in-heap bump-pointer traceRegion allocator.
package runtime
import (
"internal/goarch"
"runtime/internal/sys"
"unsafe"
)
// traceRegionAlloc is a non-thread-safe region allocator.
// It holds a linked list of traceRegionAllocBlock.
type traceRegionAlloc struct {
head *traceRegionAllocBlock
off uintptr
}
// traceRegionAllocBlock is a block in traceRegionAlloc.
//
// traceRegionAllocBlock is allocated from non-GC'd memory, so it must not
// contain heap pointers. Writes to pointers to traceRegionAllocBlocks do
// not need write barriers.
type traceRegionAllocBlock struct {
_ sys.NotInHeap
next *traceRegionAllocBlock
data [64<<10 - goarch.PtrSize]byte
}
// alloc allocates n-byte block.
func (a *traceRegionAlloc) alloc(n uintptr) *notInHeap {
n = alignUp(n, goarch.PtrSize)
if a.head == nil || a.off+n > uintptr(len(a.head.data)) {
if n > uintptr(len(a.head.data)) {
throw("traceRegion: alloc too large")
}
block := (*traceRegionAllocBlock)(sysAlloc(unsafe.Sizeof(traceRegionAllocBlock{}), &memstats.other_sys))
if block == nil {
throw("traceRegion: out of memory")
}
block.next = a.head
a.head = block
a.off = 0
}
p := &a.head.data[a.off]
a.off += n
return (*notInHeap)(unsafe.Pointer(p))
}
// drop frees all previously allocated memory and resets the allocator.
func (a *traceRegionAlloc) drop() {
for a.head != nil {
block := a.head
a.head = block.next
sysFree(unsafe.Pointer(block), unsafe.Sizeof(traceRegionAllocBlock{}), &memstats.other_sys)
}
}
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