Repo created

TMessagesProj/jni/voip/webrtc/base/posix/global_descriptors.h

@@ -0,0 +1,98 @@
+// 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/files/memory_mapped_file.h"
+#include "base/files/scoped_file.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.
+//
+// Note that this class is deprecated and passing file descriptor should ideally
+// be done through the command line and using FileDescriptorStore.
+// See https://crbugs.com/detail?id=692619
+class BASE_EXPORT GlobalDescriptors {
+ public:
+  typedef uint32_t Key;
+  struct Descriptor {
+    Descriptor(Key key, int fd);
+    Descriptor(Key key, int fd, base::MemoryMappedFile::Region region);
+
+    // Globally unique key.
+    Key key;
+    // Actual FD.
+    int fd;
+    // Optional region, defaults to kWholeFile.
+    base::MemoryMappedFile::Region region;
+  };
+  typedef std::vector<Descriptor> Mapping;
+
+  // Often we want a canonical descriptor for a given Key. In this case, we add
+  // the following constant to the key value:
+  static const int kBaseDescriptor = 3;  // 0, 1, 2 are already taken.
+
+  // 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 given a key. Returns -1 on error.
+  int MaybeGet(Key key) const;
+
+  // Returns a descriptor given a key and removes it from this class mappings.
+  // Also populates |region|.
+  // It is a fatal error if the key is not known.
+  base::ScopedFD TakeFD(Key key, base::MemoryMappedFile::Region* region);
+
+  // Get a region given a key. It is a fatal error if the key is not known.
+  base::MemoryMappedFile::Region GetRegion(Key key) const;
+
+  // Set the descriptor for the given |key|. This sets the region associated
+  // with |key| to kWholeFile.
+  void Set(Key key, int fd);
+
+  // Set the descriptor and |region| for the given |key|.
+  void Set(Key key, int fd, base::MemoryMappedFile::Region region);
+
+  void Reset(const Mapping& mapping);
+
+ private:
+  friend struct DefaultSingletonTraits<GlobalDescriptors>;
+  GlobalDescriptors();
+  ~GlobalDescriptors();
+
+  Mapping descriptors_;
+};
+
+}  // namespace base
+
+#endif  // BASE_POSIX_GLOBAL_DESCRIPTORS_H_