mirror of
https://github.com/superseriousbusiness/gotosocial.git
synced 2024-11-23 12:16:38 +00:00
63 lines
1.6 KiB
Go
63 lines
1.6 KiB
Go
|
// Copyright 2019 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.
|
||
|
|
|
||
|
|
// +build darwin dragonfly freebsd linux netbsd openbsd
|
||
|
|
|
||
|
|
package bio
|
||
|
|
|
||
|
|
import (
|
||
|
|
"runtime"
|
||
|
|
"sync/atomic"
|
||
|
|
"syscall"
|
||
|
|
)
|
||
|
|
|
||
|
|
// mmapLimit is the maximum number of mmaped regions to create before
|
||
|
|
// falling back to reading into a heap-allocated slice. This exists
|
||
|
|
// because some operating systems place a limit on the number of
|
||
|
|
// distinct mapped regions per process. As of this writing:
|
||
|
|
//
|
||
|
|
// Darwin unlimited
|
||
|
|
// DragonFly 1000000 (vm.max_proc_mmap)
|
||
|
|
// FreeBSD unlimited
|
||
|
|
// Linux 65530 (vm.max_map_count) // TODO: query /proc/sys/vm/max_map_count?
|
||
|
|
// NetBSD unlimited
|
||
|
|
// OpenBSD unlimited
|
||
|
|
var mmapLimit int32 = 1<<31 - 1
|
||
|
|
|
||
|
|
func init() {
|
||
|
|
// Linux is the only practically concerning OS.
|
||
|
|
if runtime.GOOS == "linux" {
|
||
|
|
mmapLimit = 30000
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
func (r *Reader) sliceOS(length uint64) ([]byte, bool) {
|
||
|
|
// For small slices, don't bother with the overhead of a
|
||
|
|
// mapping, especially since we have no way to unmap it.
|
||
|
|
const threshold = 16 << 10
|
||
|
|
if length < threshold {
|
||
|
|
return nil, false
|
||
|
|
}
|
||
|
|
|
||
|
|
// Have we reached the mmap limit?
|
||
|
|
if atomic.AddInt32(&mmapLimit, -1) < 0 {
|
||
|
|
atomic.AddInt32(&mmapLimit, 1)
|
||
|
|
return nil, false
|
||
|
|
}
|
||
|
|
|
||
|
|
// Page-align the offset.
|
||
|
|
off := r.Offset()
|
||
|
|
align := syscall.Getpagesize()
|
||
|
|
aoff := off &^ int64(align-1)
|
||
|
|
|
||
|
|
data, err := syscall.Mmap(int(r.f.Fd()), aoff, int(length+uint64(off-aoff)), syscall.PROT_READ, syscall.MAP_SHARED|syscall.MAP_FILE)
|
||
|
|
if err != nil {
|
||
|
|
return nil, false
|
||
|
|
}
|
||
|
|
|
||
|
|
data = data[off-aoff:]
|
||
|
|
r.MustSeek(int64(length), 1)
|
||
|
|
return data, true
|
||
|
|
}
|