tidb manual 代码
文件路径：/br/pkg/lightning/manual/manual.go
/ Copyright 2020 The LevelDB-Go and Pebble 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 manual
/ #include <stdlib.h>
import "C"
import "unsafe"
/ The go:linkname directives provides backdoor access to private functions in
/ the runtime. Below we're accessing the throw function.
/go:linkname throw runtime.throw
func throw(s string)
/ TODO(peter): Rather than relying an C malloc/free, we could fork the Go
/ runtime page allocator and allocate large chunks of memory using mmap or
/ similar.
const (
/ MaxArrayLen is a safe maximum length for slices on this architecture.
MaxArrayLen = 1<<31 - 1
)
/ New allocates a slice of size n. The returned slice is from manually managed
/ memory and MUST be released by calling Free. Failure to do so will result in
/ a memory leak.
func New(n int) []byte {
if n == 0 {
return make([]byte, 0)
}
/ We need to be conscious of the Cgo pointer passing rules:
/
/ https://golang.org/cmd/cgo/#hdr-Passing_pointers
/
/ ...
/ Note: the current implementation has a bug. While Go code is permitted
/ to write nil or a C pointer (but not a Go pointer) to C memory, the
/ current implementation may sometimes cause a runtime error if the
/ contents of the C memory appear to be a Go pointer. Therefore, avoid
/ passing uninitialized C memory to Go code if the Go code is going to
/ store pointer values in it. Zero out the memory in C before passing it
/ to Go.
ptr := C.calloc(C.size_t(n), 1)
if ptr == nil {
/ NB: throw is like panic, except it guarantees the process will be
/ terminated. The call below is exactly what the Go runtime invokes when
/ it cannot allocate memory.
throw("out of memory")
}
/ Interpret the C pointer as a pointer to a Go array, then slice.
return (*[MaxArrayLen]byte)(ptr)[:n:n]
}
/ Free frees the specified slice.
func Free(b []byte) {
if cap(b) != 0 {
if len(b) == 0 {
b = b[:cap(b)]
}
ptr := unsafe.Pointer(&b[0])
C.free(ptr)
}
}