[email protected] | cc8f146 | 2009-06-12 17:36:55 | [diff] [blame] | 1 | // 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 | |
| 17 | namespace 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. |
| 36 | class 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_ |