shared_memory.h 11.3 KB
Newer Older
gejun's avatar
gejun committed
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325
// 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_MEMORY_SHARED_MEMORY_H_
#define BASE_MEMORY_SHARED_MEMORY_H_

#include "base/build_config.h"

#include <string>

#if defined(OS_POSIX)
#include <stdio.h>
#include <sys/types.h>
#include <semaphore.h>
#endif

#include "base/base_export.h"
#include "base/basictypes.h"
#include "base/process/process_handle.h"

#if defined(OS_POSIX)
#include "base/file_descriptor_posix.h"
#include "base/file_util.h"
#include "base/files/scoped_file.h"
#endif

namespace base {

class FilePath;

// SharedMemoryHandle is a platform specific type which represents
// the underlying OS handle to a shared memory segment.
#if defined(OS_WIN)
typedef HANDLE SharedMemoryHandle;
#elif defined(OS_POSIX)
// A SharedMemoryId is sufficient to identify a given shared memory segment on a
// system, but insufficient to map it.
typedef FileDescriptor SharedMemoryHandle;
typedef ino_t SharedMemoryId;
#endif

// Options for creating a shared memory object.
struct SharedMemoryCreateOptions {
  SharedMemoryCreateOptions()
      : name_deprecated(NULL),
        size(0),
        open_existing_deprecated(false),
        executable(false),
        share_read_only(false) {}

  // DEPRECATED (crbug.com/345734):
  // If NULL, the object is anonymous.  This pointer is owned by the caller
  // and must live through the call to Create().
  const std::string* name_deprecated;

  // Size of the shared memory object to be created.
  // When opening an existing object, this has no effect.
  size_t size;

  // DEPRECATED (crbug.com/345734):
  // If true, and the shared memory already exists, Create() will open the
  // existing shared memory and ignore the size parameter.  If false,
  // shared memory must not exist.  This flag is meaningless unless
  // name_deprecated is non-NULL.
  bool open_existing_deprecated;

  // If true, mappings might need to be made executable later.
  bool executable;

  // If true, the file can be shared read-only to a process.
  bool share_read_only;
};

// Platform abstraction for shared memory.  Provides a C++ wrapper
// around the OS primitive for a memory mapped file.
class BASE_EXPORT SharedMemory {
 public:
  SharedMemory();

#if defined(OS_WIN)
  // Similar to the default constructor, except that this allows for
  // calling LockDeprecated() to acquire the named mutex before either Create or
  // Open are called on Windows.
  explicit SharedMemory(const std::wstring& name);
#endif

  // Create a new SharedMemory object from an existing, open
  // shared memory file.
  //
  // WARNING: This does not reduce the OS-level permissions on the handle; it
  // only affects how the SharedMemory will be mmapped.  Use
  // ShareReadOnlyToProcess to drop permissions.  TODO(jln,jyasskin): DCHECK
  // that |read_only| matches the permissions of the handle.
  SharedMemory(SharedMemoryHandle handle, bool read_only);

  // Create a new SharedMemory object from an existing, open
  // shared memory file that was created by a remote process and not shared
  // to the current process.
  SharedMemory(SharedMemoryHandle handle, bool read_only,
               ProcessHandle process);

  // Closes any open files.
  ~SharedMemory();

  // Return true iff the given handle is valid (i.e. not the distingished
  // invalid value; NULL for a HANDLE and -1 for a file descriptor)
  static bool IsHandleValid(const SharedMemoryHandle& handle);

  // Returns invalid handle (see comment above for exact definition).
  static SharedMemoryHandle NULLHandle();

  // Closes a shared memory handle.
  static void CloseHandle(const SharedMemoryHandle& handle);

  // Returns the maximum number of handles that can be open at once per process.
  static size_t GetHandleLimit();

  // Creates a shared memory object as described by the options struct.
  // Returns true on success and false on failure.
  bool Create(const SharedMemoryCreateOptions& options);

  // Creates and maps an anonymous shared memory segment of size size.
  // Returns true on success and false on failure.
  bool CreateAndMapAnonymous(size_t size);

  // Creates an anonymous shared memory segment of size size.
  // Returns true on success and false on failure.
  bool CreateAnonymous(size_t size) {
    SharedMemoryCreateOptions options;
    options.size = size;
    return Create(options);
  }

  // DEPRECATED (crbug.com/345734):
  // Creates or opens a shared memory segment based on a name.
  // If open_existing is true, and the shared memory already exists,
  // opens the existing shared memory and ignores the size parameter.
  // If open_existing is false, shared memory must not exist.
  // size is the size of the block to be created.
  // Returns true on success, false on failure.
  bool CreateNamedDeprecated(
      const std::string& name, bool open_existing, size_t size) {
    SharedMemoryCreateOptions options;
    options.name_deprecated = &name;
    options.open_existing_deprecated = open_existing;
    options.size = size;
    return Create(options);
  }

  // Deletes resources associated with a shared memory segment based on name.
  // Not all platforms require this call.
  bool Delete(const std::string& name);

  // Opens a shared memory segment based on a name.
  // If read_only is true, opens for read-only access.
  // Returns true on success, false on failure.
  bool Open(const std::string& name, bool read_only);

  // Maps the shared memory into the caller's address space.
  // Returns true on success, false otherwise.  The memory address
  // is accessed via the memory() accessor.  The mapped address is guaranteed to
  // have an alignment of at least MAP_MINIMUM_ALIGNMENT. This method will fail
  // if this object is currently mapped.
  bool Map(size_t bytes) {
    return MapAt(0, bytes);
  }

  // Same as above, but with |offset| to specify from begining of the shared
  // memory block to map.
  // |offset| must be alignent to value of |SysInfo::VMAllocationGranularity()|.
  bool MapAt(off_t offset, size_t bytes);
  enum { MAP_MINIMUM_ALIGNMENT = 32 };

  // Unmaps the shared memory from the caller's address space.
  // Returns true if successful; returns false on error or if the
  // memory is not mapped.
  bool Unmap();

  // The size requested when the map is first created.
  size_t requested_size() const { return requested_size_; }

  // The actual size of the mapped memory (may be larger than requested).
  size_t mapped_size() const { return mapped_size_; }

  // Gets a pointer to the opened memory space if it has been
  // Mapped via Map().  Returns NULL if it is not mapped.
  void *memory() const { return memory_; }

  // Returns the underlying OS handle for this segment.
  // Use of this handle for anything other than an opaque
  // identifier is not portable.
  SharedMemoryHandle handle() const;

#if defined(OS_POSIX) && !defined(OS_NACL)
  // Returns a unique identifier for this shared memory segment. Inode numbers
  // are technically only unique to a single filesystem. However, we always
  // allocate shared memory backing files from the same directory, so will end
  // up on the same filesystem.
  SharedMemoryId id() const { return inode_; }
#endif

  // Closes the open shared memory segment.
  // It is safe to call Close repeatedly.
  void Close();

  // Shares the shared memory to another process.  Attempts to create a
  // platform-specific new_handle which can be used in a remote process to read
  // the shared memory file.  new_handle is an output parameter to receive the
  // handle for use in the remote process.
  //
  // |*this| must have been initialized using one of the Create*() or Open()
  // methods with share_read_only=true. If it was constructed from a
  // SharedMemoryHandle, this call will CHECK-fail.
  //
  // Returns true on success, false otherwise.
  bool ShareReadOnlyToProcess(ProcessHandle process,
                              SharedMemoryHandle* new_handle) {
    return ShareToProcessCommon(process, new_handle, false, SHARE_READONLY);
  }

  // Logically equivalent to:
  //   bool ok = ShareReadOnlyToProcess(process, new_handle);
  //   Close();
  //   return ok;
  // Note that the memory is unmapped by calling this method, regardless of the
  // return value.
  bool GiveReadOnlyToProcess(ProcessHandle process,
                             SharedMemoryHandle* new_handle) {
    return ShareToProcessCommon(process, new_handle, true, SHARE_READONLY);
  }

  // Shares the shared memory to another process.  Attempts
  // to create a platform-specific new_handle which can be
  // used in a remote process to access the shared memory
  // file.  new_handle is an output parameter to receive
  // the handle for use in the remote process.
  // Returns true on success, false otherwise.
  bool ShareToProcess(ProcessHandle process,
                      SharedMemoryHandle* new_handle) {
    return ShareToProcessCommon(process, new_handle, false, SHARE_CURRENT_MODE);
  }

  // Logically equivalent to:
  //   bool ok = ShareToProcess(process, new_handle);
  //   Close();
  //   return ok;
  // Note that the memory is unmapped by calling this method, regardless of the
  // return value.
  bool GiveToProcess(ProcessHandle process,
                     SharedMemoryHandle* new_handle) {
    return ShareToProcessCommon(process, new_handle, true, SHARE_CURRENT_MODE);
  }

  // DEPRECATED (crbug.com/345734):
  // Locks the shared memory.
  //
  // WARNING: on POSIX the memory locking primitive only works across
  // processes, not across threads.  The LockDeprecated method is not currently
  // used in inner loops, so we protect against multiple threads in a
  // critical section using a class global lock.
  void LockDeprecated();

  // DEPRECATED (crbug.com/345734):
  // Releases the shared memory lock.
  void UnlockDeprecated();

 private:
#if defined(OS_POSIX) && !defined(OS_NACL)
#if !defined(OS_ANDROID)
  bool PrepareMapFile(ScopedFILE fp, ScopedFD readonly);
  bool FilePathForMemoryName(const std::string& mem_name, FilePath* path);
#endif
  void LockOrUnlockCommon(int function);
#endif  // defined(OS_POSIX) && !defined(OS_NACL)
  enum ShareMode {
    SHARE_READONLY,
    SHARE_CURRENT_MODE,
  };
  bool ShareToProcessCommon(ProcessHandle process,
                            SharedMemoryHandle* new_handle,
                            bool close_self,
                            ShareMode);

#if defined(OS_WIN)
  std::wstring       name_;
  HANDLE             mapped_file_;
#elif defined(OS_POSIX)
  int                mapped_file_;
  int                readonly_mapped_file_;
  ino_t              inode_;
#endif
  size_t             mapped_size_;
  void*              memory_;
  bool               read_only_;
  size_t             requested_size_;
#if !defined(OS_POSIX)
  HANDLE             lock_;
#endif

  DISALLOW_COPY_AND_ASSIGN(SharedMemory);
};

// DEPRECATED (crbug.com/345734):
// A helper class that acquires the shared memory lock while
// the SharedMemoryAutoLockDeprecated is in scope.
class SharedMemoryAutoLockDeprecated {
 public:
  explicit SharedMemoryAutoLockDeprecated(SharedMemory* shared_memory)
      : shared_memory_(shared_memory) {
    shared_memory_->LockDeprecated();
  }

  ~SharedMemoryAutoLockDeprecated() {
    shared_memory_->UnlockDeprecated();
  }

 private:
  SharedMemory* shared_memory_;
  DISALLOW_COPY_AND_ASSIGN(SharedMemoryAutoLockDeprecated);
};

}  // namespace base

#endif  // BASE_MEMORY_SHARED_MEMORY_H_