well-goknown/vendor/github.com/gobwas/pool/pbytes/pool_sanitize.go

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// +build pool_sanitize
package pbytes
import (
"reflect"
"runtime"
"sync/atomic"
"syscall"
"unsafe"
"golang.org/x/sys/unix"
)
const magic = uint64(0x777742)
type guard struct {
magic uint64
size int
owners int32
}
const guardSize = int(unsafe.Sizeof(guard{}))
type Pool struct {
min, max int
}
func New(min, max int) *Pool {
return &Pool{min, max}
}
// Get returns probably reused slice of bytes with at least capacity of c and
// exactly len of n.
func (p *Pool) Get(n, c int) []byte {
if n > c {
panic("requested length is greater than capacity")
}
pageSize := syscall.Getpagesize()
pages := (c+guardSize)/pageSize + 1
size := pages * pageSize
bts := alloc(size)
g := (*guard)(unsafe.Pointer(&bts[0]))
*g = guard{
magic: magic,
size: size,
owners: 1,
}
return bts[guardSize : guardSize+n]
}
func (p *Pool) GetCap(c int) []byte { return p.Get(0, c) }
func (p *Pool) GetLen(n int) []byte { return Get(n, n) }
// Put returns given slice to reuse pool.
func (p *Pool) Put(bts []byte) {
hdr := *(*reflect.SliceHeader)(unsafe.Pointer(&bts))
ptr := hdr.Data - uintptr(guardSize)
g := (*guard)(unsafe.Pointer(ptr))
if g.magic != magic {
panic("unknown slice returned to the pool")
}
if n := atomic.AddInt32(&g.owners, -1); n < 0 {
panic("multiple Put() detected")
}
// Disable read and write on bytes memory pages. This will cause panic on
// incorrect access to returned slice.
mprotect(ptr, false, false, g.size)
runtime.SetFinalizer(&bts, func(b *[]byte) {
mprotect(ptr, true, true, g.size)
free(*(*[]byte)(unsafe.Pointer(&reflect.SliceHeader{
Data: ptr,
Len: g.size,
Cap: g.size,
})))
})
}
func alloc(n int) []byte {
b, err := unix.Mmap(-1, 0, n, unix.PROT_READ|unix.PROT_WRITE|unix.PROT_EXEC, unix.MAP_SHARED|unix.MAP_ANONYMOUS)
if err != nil {
panic(err.Error())
}
return b
}
func free(b []byte) {
if err := unix.Munmap(b); err != nil {
panic(err.Error())
}
}
func mprotect(ptr uintptr, r, w bool, size int) {
// Need to avoid "EINVAL addr is not a valid pointer,
// or not a multiple of PAGESIZE."
start := ptr & ^(uintptr(syscall.Getpagesize() - 1))
prot := uintptr(syscall.PROT_EXEC)
switch {
case r && w:
prot |= syscall.PROT_READ | syscall.PROT_WRITE
case r:
prot |= syscall.PROT_READ
case w:
prot |= syscall.PROT_WRITE
}
_, _, err := syscall.Syscall(syscall.SYS_MPROTECT,
start, uintptr(size), prot,
)
if err != 0 {
panic(err.Error())
}
}