blob: b45093ec862b8a2fb4507110571d0f10a53338e9 [file] [log] [blame]
// 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.
// Simple not-in-heap bump-pointer traceRegion allocator.
package runtime
import (
"internal/runtime/atomic"
"internal/runtime/sys"
"unsafe"
)
// traceRegionAlloc is a thread-safe region allocator.
// It holds a linked list of traceRegionAllocBlock.
type traceRegionAlloc struct {
lock mutex
dropping atomic.Bool // For checking invariants.
current atomic.UnsafePointer // *traceRegionAllocBlock
full *traceRegionAllocBlock
}
// 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
traceRegionAllocBlockHeader
data [traceRegionAllocBlockData]byte
}
type traceRegionAllocBlockHeader struct {
next *traceRegionAllocBlock
off atomic.Uintptr
}
const traceRegionAllocBlockData = 64<<10 - unsafe.Sizeof(traceRegionAllocBlockHeader{})
// alloc allocates n-byte block. The block is always aligned to 8 bytes, regardless of platform.
func (a *traceRegionAlloc) alloc(n uintptr) *notInHeap {
n = alignUp(n, 8)
if n > traceRegionAllocBlockData {
throw("traceRegion: alloc too large")
}
if a.dropping.Load() {
throw("traceRegion: alloc with concurrent drop")
}
// Try to bump-pointer allocate into the current block.
block := (*traceRegionAllocBlock)(a.current.Load())
if block != nil {
r := block.off.Add(n)
if r <= uintptr(len(block.data)) {
return (*notInHeap)(unsafe.Pointer(&block.data[r-n]))
}
}
// Try to install a new block.
lock(&a.lock)
// Check block again under the lock. Someone may
// have gotten here first.
block = (*traceRegionAllocBlock)(a.current.Load())
if block != nil {
r := block.off.Add(n)
if r <= uintptr(len(block.data)) {
unlock(&a.lock)
return (*notInHeap)(unsafe.Pointer(&block.data[r-n]))
}
// Add the existing block to the full list.
block.next = a.full
a.full = block
}
// Allocate a new block.
block = (*traceRegionAllocBlock)(sysAlloc(unsafe.Sizeof(traceRegionAllocBlock{}), &memstats.other_sys))
if block == nil {
throw("traceRegion: out of memory")
}
// Allocate space for our current request, so we always make
// progress.
block.off.Store(n)
x := (*notInHeap)(unsafe.Pointer(&block.data[0]))
// Publish the new block.
a.current.Store(unsafe.Pointer(block))
unlock(&a.lock)
return x
}
// drop frees all previously allocated memory and resets the allocator.
//
// drop is not safe to call concurrently with other calls to drop or with calls to alloc. The caller
// must ensure that it is not possible for anything else to be using the same structure.
func (a *traceRegionAlloc) drop() {
a.dropping.Store(true)
for a.full != nil {
block := a.full
a.full = block.next
sysFree(unsafe.Pointer(block), unsafe.Sizeof(traceRegionAllocBlock{}), &memstats.other_sys)
}
if current := a.current.Load(); current != nil {
sysFree(current, unsafe.Sizeof(traceRegionAllocBlock{}), &memstats.other_sys)
a.current.Store(nil)
}
a.dropping.Store(false)
}