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 Reset(const Mapping & mapping)53 void Reset(const Mapping& mapping) { 54 descriptors_ = mapping; 55 } 56 57 private: GlobalDescriptors()58 GlobalDescriptors() { } 59 friend struct DefaultSingletonTraits<GlobalDescriptors>; 60 61 Mapping descriptors_; 62 }; 63 64 } // namespace base 65 66 #endif // BASE_GLOBAL_DESCRIPTORS_POSIX_H_ 67