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. 4 5 #ifndef BASE_GLOBAL_DESCRIPTORS_POSIX_H_ 6 #define BASE_GLOBAL_DESCRIPTORS_POSIX_H_ 7 #pragma once 8 9 #include "build/build_config.h" 10 11 #include <vector> 12 #include <utility> 13 14 #include <stdint.h> 15 16 #include "base/memory/singleton.h" 17 18 namespace base { 19 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 22 // examples. 23 // 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. 28 // 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. 31 // 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 36 // collide. 37 class GlobalDescriptors { 38 public: 39 typedef uint32_t Key; 40 typedef std::vector<std::pair<Key, int> > Mapping; 41 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. 45 46 // Return the singleton instance of GlobalDescriptors. 47 static GlobalDescriptors* GetInstance(); 48 49 // Get a descriptor given a key. It is a fatal error if the key is not known. 50 int Get(Key key) const; 51 52 // Get a descriptor give a key. Returns -1 on error. 53 int MaybeGet(Key key) const; 54 55 // Set the descriptor for the given key. 56 void Set(Key key, int fd); 57 58 void Reset(const Mapping& mapping); 59 60 private: 61 friend struct DefaultSingletonTraits<GlobalDescriptors>; 62 GlobalDescriptors(); 63 ~GlobalDescriptors(); 64 65 Mapping descriptors_; 66 }; 67 68 } // namespace base 69 70 #endif // BASE_GLOBAL_DESCRIPTORS_POSIX_H_ 71
