// Copyright (c) 2012 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_POSIX_GLOBAL_DESCRIPTORS_H_
#define BASE_POSIX_GLOBAL_DESCRIPTORS_H_
#include "build/build_config.h"
#include <vector>
#include <utility>
#include <stdint.h>
#include "base/memory/singleton.h"
namespace base {
// It's common practice to install file descriptors into well known slot
// numbers before execing a child; stdin, stdout and stderr are ubiqutous
// examples.
//
// However, when using a zygote model, this becomes troublesome. Since the
// descriptors which need to be in these slots generally aren't known, any code
// could open a resource and take one of the reserved descriptors. Simply
// overwriting the slot isn't a viable solution.
//
// We could try to fill the reserved slots as soon as possible, but this is a
// fragile solution since global constructors etc are able to open files.
//
// Instead, we retreat from the idea of installing descriptors in specific
// slots and add a layer of indirection in the form of this singleton object.
// It maps from an abstract key to a descriptor. If independent modules each
// need to define keys, then values should be chosen randomly so as not to
// collide.
class BASE_EXPORT GlobalDescriptors {
public:
typedef uint32_t Key;
typedef std::pair<Key, int> KeyFDPair;
typedef std::vector<KeyFDPair> Mapping;
// Often we want a canonical descriptor for a given Key. In this case, we add
// the following constant to the key value:
#if !defined(OS_ANDROID)
static const int kBaseDescriptor = 3; // 0, 1, 2 are already taken.
#else
static const int kBaseDescriptor = 4; // 3 used by __android_log_write().
#endif
// Return the singleton instance of GlobalDescriptors.
static GlobalDescriptors* GetInstance();
// Get a descriptor given a key. It is a fatal error if the key is not known.
int Get(Key key) const;
// Get a descriptor give a key. Returns -1 on error.
int MaybeGet(Key key) const;
// Set the descriptor for the given key.
void Set(Key key, int fd);
void Reset(const Mapping& mapping);
private:
friend struct DefaultSingletonTraits<GlobalDescriptors>;
GlobalDescriptors();
~GlobalDescriptors();
Mapping descriptors_;
};
} // namespace base
#endif // BASE_POSIX_GLOBAL_DESCRIPTORS_H_