base/memory/shared_memory.h

   1 // Copyright (c) 2012 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_MEMORY_SHARED_MEMORY_H_
   6 #define BASE_MEMORY_SHARED_MEMORY_H_
   7
   8 #include "build/build_config.h"
   9
  10 #include <string>
  11
  12 #if defined(OS_POSIX)
  13 #include <stdio.h>
  14 #include <sys/types.h>
  15 #include <semaphore.h>
  16 #endif
  17
  18 #include "base/base_export.h"
  19 #include "base/basictypes.h"
  20 #include "base/process/process_handle.h"
  21
  22 #if defined(OS_POSIX)
  23 #include "base/file_descriptor_posix.h"
  24 #include "base/files/file_util.h"
  25 #include "base/files/scoped_file.h"
  26 #endif
  27
  28 namespace base {
  29
  30 class FilePath;
  31
  32 // SharedMemoryHandle is a platform specific type which represents
  33 // the underlying OS handle to a shared memory segment.
  34 #if defined(OS_WIN)
  35 typedef HANDLE SharedMemoryHandle;
  36 #elif defined(OS_POSIX)
  37 typedef FileDescriptor SharedMemoryHandle;
  38 #endif
  39
  40 // Options for creating a shared memory object.
  41 struct SharedMemoryCreateOptions {
  42   SharedMemoryCreateOptions()
  43       : name_deprecated(NULL),
  44         size(0),
  45         open_existing_deprecated(false),
  46         executable(false),
  47         share_read_only(false) {}
  48
  49   // DEPRECATED (crbug.com/345734):
  50   // If NULL, the object is anonymous.  This pointer is owned by the caller
  51   // and must live through the call to Create().
  52   const std::string* name_deprecated;
  53
  54   // Size of the shared memory object to be created.
  55   // When opening an existing object, this has no effect.
  56   size_t size;
  57
  58   // DEPRECATED (crbug.com/345734):
  59   // If true, and the shared memory already exists, Create() will open the
  60   // existing shared memory and ignore the size parameter.  If false,
  61   // shared memory must not exist.  This flag is meaningless unless
  62   // name_deprecated is non-NULL.
  63   bool open_existing_deprecated;
  64
  65   // If true, mappings might need to be made executable later.
  66   bool executable;
  67
  68   // If true, the file can be shared read-only to a process.
  69   bool share_read_only;
  70 };
  71
  72 // Platform abstraction for shared memory.  Provides a C++ wrapper
  73 // around the OS primitive for a memory mapped file.
  74 class BASE_EXPORT SharedMemory {
  75  public:
  76   SharedMemory();
  77
  78 #if defined(OS_WIN)
  79   // Similar to the default constructor, except that this allows for
  80   // calling LockDeprecated() to acquire the named mutex before either Create or
  81   // Open are called on Windows.
  82   explicit SharedMemory(const std::wstring& name);
  83 #endif
  84
  85   // Create a new SharedMemory object from an existing, open
  86   // shared memory file.
  87   //
  88   // WARNING: This does not reduce the OS-level permissions on the handle; it
  89   // only affects how the SharedMemory will be mmapped.  Use
  90   // ShareReadOnlyToProcess to drop permissions.  TODO(jln,jyasskin): DCHECK
  91   // that |read_only| matches the permissions of the handle.
  92   SharedMemory(SharedMemoryHandle handle, bool read_only);
  93
  94   // Create a new SharedMemory object from an existing, open
  95   // shared memory file that was created by a remote process and not shared
  96   // to the current process.
  97   SharedMemory(SharedMemoryHandle handle, bool read_only,
  98                ProcessHandle process);
  99
 100   // Closes any open files.
 101   ~SharedMemory();
 102
 103   // Return true iff the given handle is valid (i.e. not the distingished
 104   // invalid value; NULL for a HANDLE and -1 for a file descriptor)
 105   static bool IsHandleValid(const SharedMemoryHandle& handle);
 106
 107   // Returns invalid handle (see comment above for exact definition).
 108   static SharedMemoryHandle NULLHandle();
 109
 110   // Closes a shared memory handle.
 111   static void CloseHandle(const SharedMemoryHandle& handle);
 112
 113   // Returns the maximum number of handles that can be open at once per process.
 114   static size_t GetHandleLimit();
 115
 116   // Duplicates The underlying OS primitive. Returns NULLHandle() on failure.
 117   // The caller is responsible for destroying the duplicated OS primitive.
 118   static SharedMemoryHandle DuplicateHandle(const SharedMemoryHandle& handle);
 119
 120 #if defined(OS_POSIX)
 121   // This method requires that the SharedMemoryHandle is backed by a POSIX fd.
 122   static int GetFdFromSharedMemoryHandle(const SharedMemoryHandle& handle);
 123 #endif
 124
 125 #if defined(OS_POSIX) && !defined(OS_ANDROID)
 126   // Returns the size of the shared memory region referred to by |handle|.
 127   // Returns '-1' on a failure to determine the size.
 128   static int GetSizeFromSharedMemoryHandle(const SharedMemoryHandle& handle);
 129 #endif  // defined(OS_POSIX) && !defined(OS_ANDROID)
 130
 131   // Creates a shared memory object as described by the options struct.
 132   // Returns true on success and false on failure.
 133   bool Create(const SharedMemoryCreateOptions& options);
 134
 135   // Creates and maps an anonymous shared memory segment of size size.
 136   // Returns true on success and false on failure.
 137   bool CreateAndMapAnonymous(size_t size);
 138
 139   // Creates an anonymous shared memory segment of size size.
 140   // Returns true on success and false on failure.
 141   bool CreateAnonymous(size_t size) {
 142     SharedMemoryCreateOptions options;
 143     options.size = size;
 144     return Create(options);
 145   }
 146
 147   // DEPRECATED (crbug.com/345734):
 148   // Creates or opens a shared memory segment based on a name.
 149   // If open_existing is true, and the shared memory already exists,
 150   // opens the existing shared memory and ignores the size parameter.
 151   // If open_existing is false, shared memory must not exist.
 152   // size is the size of the block to be created.
 153   // Returns true on success, false on failure.
 154   bool CreateNamedDeprecated(
 155       const std::string& name, bool open_existing, size_t size) {
 156     SharedMemoryCreateOptions options;
 157     options.name_deprecated = &name;
 158     options.open_existing_deprecated = open_existing;
 159     options.size = size;
 160     return Create(options);
 161   }
 162
 163   // Deletes resources associated with a shared memory segment based on name.
 164   // Not all platforms require this call.
 165   bool Delete(const std::string& name);
 166
 167   // Opens a shared memory segment based on a name.
 168   // If read_only is true, opens for read-only access.
 169   // Returns true on success, false on failure.
 170   bool Open(const std::string& name, bool read_only);
 171
 172   // Maps the shared memory into the caller's address space.
 173   // Returns true on success, false otherwise.  The memory address
 174   // is accessed via the memory() accessor.  The mapped address is guaranteed to
 175   // have an alignment of at least MAP_MINIMUM_ALIGNMENT. This method will fail
 176   // if this object is currently mapped.
 177   bool Map(size_t bytes) {
 178     return MapAt(0, bytes);
 179   }
 180
 181   // Same as above, but with |offset| to specify from begining of the shared
 182   // memory block to map.
 183   // |offset| must be alignent to value of |SysInfo::VMAllocationGranularity()|.
 184   bool MapAt(off_t offset, size_t bytes);
 185   enum { MAP_MINIMUM_ALIGNMENT = 32 };
 186
 187   // Unmaps the shared memory from the caller's address space.
 188   // Returns true if successful; returns false on error or if the
 189   // memory is not mapped.
 190   bool Unmap();
 191
 192   // The size requested when the map is first created.
 193   size_t requested_size() const { return requested_size_; }
 194
 195   // The actual size of the mapped memory (may be larger than requested).
 196   size_t mapped_size() const { return mapped_size_; }
 197
 198   // Gets a pointer to the opened memory space if it has been
 199   // Mapped via Map().  Returns NULL if it is not mapped.
 200   void *memory() const { return memory_; }
 201
 202   // Returns the underlying OS handle for this segment.
 203   // Use of this handle for anything other than an opaque
 204   // identifier is not portable.
 205   SharedMemoryHandle handle() const;
 206
 207   // Closes the open shared memory segment. The memory will remain mapped if
 208   // it was previously mapped.
 209   // It is safe to call Close repeatedly.
 210   void Close();
 211
 212   // Shares the shared memory to another process.  Attempts to create a
 213   // platform-specific new_handle which can be used in a remote process to read
 214   // the shared memory file.  new_handle is an output parameter to receive the
 215   // handle for use in the remote process.
 216   //
 217   // |*this| must have been initialized using one of the Create*() or Open()
 218   // methods with share_read_only=true. If it was constructed from a
 219   // SharedMemoryHandle, this call will CHECK-fail.
 220   //
 221   // Returns true on success, false otherwise.
 222   bool ShareReadOnlyToProcess(ProcessHandle process,
 223                               SharedMemoryHandle* new_handle) {
 224     return ShareToProcessCommon(process, new_handle, false, SHARE_READONLY);
 225   }
 226
 227   // Logically equivalent to:
 228   //   bool ok = ShareReadOnlyToProcess(process, new_handle);
 229   //   Close();
 230   //   return ok;
 231   // Note that the memory is unmapped by calling this method, regardless of the
 232   // return value.
 233   bool GiveReadOnlyToProcess(ProcessHandle process,
 234                              SharedMemoryHandle* new_handle) {
 235     return ShareToProcessCommon(process, new_handle, true, SHARE_READONLY);
 236   }
 237
 238   // Shares the shared memory to another process.  Attempts
 239   // to create a platform-specific new_handle which can be
 240   // used in a remote process to access the shared memory
 241   // file.  new_handle is an output parameter to receive
 242   // the handle for use in the remote process.
 243   // Returns true on success, false otherwise.
 244   bool ShareToProcess(ProcessHandle process,
 245                       SharedMemoryHandle* new_handle) {
 246     return ShareToProcessCommon(process, new_handle, false, SHARE_CURRENT_MODE);
 247   }
 248
 249   // Logically equivalent to:
 250   //   bool ok = ShareToProcess(process, new_handle);
 251   //   Close();
 252   //   return ok;
 253   // Note that the memory is unmapped by calling this method, regardless of the
 254   // return value.
 255   bool GiveToProcess(ProcessHandle process,
 256                      SharedMemoryHandle* new_handle) {
 257     return ShareToProcessCommon(process, new_handle, true, SHARE_CURRENT_MODE);
 258   }
 259
 260  private:
 261 #if defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_ANDROID)
 262   bool PrepareMapFile(ScopedFILE fp, ScopedFD readonly);
 263   bool FilePathForMemoryName(const std::string& mem_name, FilePath* path);
 264 #endif  // defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_ANDROID)
 265   enum ShareMode {
 266     SHARE_READONLY,
 267     SHARE_CURRENT_MODE,
 268   };
 269   bool ShareToProcessCommon(ProcessHandle process,
 270                             SharedMemoryHandle* new_handle,
 271                             bool close_self,
 272                             ShareMode);
 273
 274 #if defined(OS_WIN)
 275   std::wstring       name_;
 276   HANDLE             mapped_file_;
 277 #elif defined(OS_POSIX)
 278   int                mapped_file_;
 279   int                readonly_mapped_file_;
 280 #endif
 281   size_t             mapped_size_;
 282   void*              memory_;
 283   bool               read_only_;
 284   size_t             requested_size_;
 285
 286   DISALLOW_COPY_AND_ASSIGN(SharedMemory);
 287 };
 288 }  // namespace base
 289
 290 #endif  // BASE_MEMORY_SHARED_MEMORY_H_