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[email protected]cc8f1462009-06-12 17:36:551// Copyright (c) 2009 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef BASE_GLOBAL_DESCRIPTORS_POSIX_H_
6#define BASE_GLOBAL_DESCRIPTORS_POSIX_H_
7
8#include "build/build_config.h"
9
10#include <vector>
11#include <utility>
12
13#include <stdint.h>
14
15#include "base/singleton.h"
16
17namespace base {
18
19// It's common practice to install file descriptors into well known slot
20// numbers before execing a child; stdin, stdout and stderr are ubiqutous
21// examples.
22//
23// However, when using a zygote model, this becomes troublesome. Since the
24// descriptors which need to be in these slots generally aren't known, any code
25// could open a resource and take one of the reserved descriptors. Simply
26// overwriting the slot isn't a viable solution.
27//
28// We could try to fill the reserved slots as soon as possible, but this is a
29// fragile solution since global constructors etc are able to open files.
30//
31// Instead, we retreat from the idea of installing descriptors in specific
32// slots and add a layer of indirection in the form of this singleton object.
33// It maps from an abstract key to a descriptor. If independent modules each
34// need to define keys, then values should be chosen randomly so as not to
35// collide.
36class GlobalDescriptors {
37 public:
38 typedef uint32_t Key;
39 // Often we want a canonical descriptor for a given Key. In this case, we add
40 // the following constant to the key value:
41 static const int kBaseDescriptor = 3; // 0, 1, 2 are already taken.
42
43 // Get a descriptor given a key. It is a fatal error if the key is not known.
44 int Get(Key key) const;
45 // Get a descriptor give a key. Returns -1 on error.
46 int MaybeGet(Key key) const;
47
48 typedef std::vector<std::pair<Key, int> > Mapping;
49
50 // Set the descriptor for the given key.
51 void Set(Key key, int fd);
52
53 void Reset(const Mapping& mapping) {
54 descriptors_ = mapping;
55 }
56
57 private:
58 GlobalDescriptors() { }
59 friend struct DefaultSingletonTraits<GlobalDescriptors>;
60
61 Mapping descriptors_;
62};
63
64} // namespace base
65
66#endif // BASE_GLOBAL_DESCRIPTORS_POSIX_H_