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