/
mmf_linux.go
93 lines (83 loc) · 3.13 KB
/
mmf_linux.go
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
//go:build linux || darwin
// +build linux darwin
// Copyright © 2017 Microsoft <wastore@microsoft.com>
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package common
import (
"os"
"sync"
"syscall"
)
const lineEnding = "\n"
type MMF struct {
// slice represents the actual memory mapped buffer
slice []byte
// defines whether source has been mapped or not
isMapped bool
// This lock exists to fix a bug in Go's Http Client. Because the http
// client executes some operations asynchronously (via goroutines), it
// sometimes attempts to read from the http request stream AFTER the MMF
// is unmapped. This lock guards against the access violation panic.
// When the MMF is created, all readers can take the shared (read) access
// on this lock. When the MMF is no longer needed, exclusive (write) access
// it requested and once obtained, the MMF is unmapped. If the http client
// attempts to read again the request body again, our pacer code sees that
// isMapped is false and gracefully fails the http request (avoiding the
// access violation panic).
lock sync.RWMutex
}
func NewMMF(file *os.File, writable bool, offset int64, length int64) (*MMF, error) {
prot, flags := syscall.PROT_READ, syscall.MAP_SHARED // Assume read-only
if writable {
prot, flags = syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED
}
addr, err := syscall.Mmap(int(file.Fd()), offset, int(length), prot, flags)
if !writable {
_ = syscall.Madvise(addr, syscall.MADV_SEQUENTIAL|syscall.MADV_WILLNEED)
}
return &MMF{slice: (addr), isMapped: true, lock: sync.RWMutex{}}, err
}
// To unmap, we need exclusive (write) access to the MMF and
// then we set isMapped to false so that future readers know
// the MMF is unusable.
func (m *MMF) Unmap() {
m.lock.Lock()
err := syscall.Munmap(m.slice)
m.slice = nil
PanicIfErr(err)
m.isMapped = false
m.lock.Unlock()
}
func (m *MMF) UseMMF() bool {
m.lock.RLock()
if !m.isMapped {
m.lock.RUnlock()
return false
}
return true
}
// RUnlock unlocks the held lock
func (m *MMF) UnuseMMF() {
m.lock.RUnlock()
}
// Slice() returns the memory mapped byte slice
func (m *MMF) Slice() []byte {
return m.slice
}