1 // Copyright (c) 2011 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.
5 #ifndef BASE_GLOBAL_DESCRIPTORS_POSIX_H_
6 #define BASE_GLOBAL_DESCRIPTORS_POSIX_H_
9 #include "build/build_config.h"
16 #include "base/memory/singleton.h"
20 // It's common practice to install file descriptors into well known slot
21 // numbers before execing a child; stdin, stdout and stderr are ubiqutous
24 // However, when using a zygote model, this becomes troublesome. Since the
25 // descriptors which need to be in these slots generally aren't known, any code
26 // could open a resource and take one of the reserved descriptors. Simply
27 // overwriting the slot isn't a viable solution.
29 // We could try to fill the reserved slots as soon as possible, but this is a
30 // fragile solution since global constructors etc are able to open files.
32 // Instead, we retreat from the idea of installing descriptors in specific
33 // slots and add a layer of indirection in the form of this singleton object.
34 // It maps from an abstract key to a descriptor. If independent modules each
35 // need to define keys, then values should be chosen randomly so as not to
37 class BASE_API GlobalDescriptors
{
40 typedef std::vector
<std::pair
<Key
, int> > Mapping
;
42 // Often we want a canonical descriptor for a given Key. In this case, we add
43 // the following constant to the key value:
44 static const int kBaseDescriptor
= 3; // 0, 1, 2 are already taken.
46 // Return the singleton instance of GlobalDescriptors.
47 static GlobalDescriptors
* GetInstance();
49 // Get a descriptor given a key. It is a fatal error if the key is not known.
50 int Get(Key key
) const;
52 // Get a descriptor give a key. Returns -1 on error.
53 int MaybeGet(Key key
) const;
55 // Set the descriptor for the given key.
56 void Set(Key key
, int fd
);
58 void Reset(const Mapping
& mapping
);
61 friend struct DefaultSingletonTraits
<GlobalDescriptors
>;
70 #endif // BASE_GLOBAL_DESCRIPTORS_POSIX_H_