blob: 2eb9ee29223fa32b01a713aa9a0f63ddfd264838 [file] [log] [blame]
// 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.
#include <stddef.h>
#include <string>
#include "base/base_export.h"
#include "base/hash.h"
#include "base/macros.h"
#include "base/memory/shared_memory_handle.h"
#include "base/process/process_handle.h"
#include "base/strings/string16.h"
#include "build/build_config.h"
#if defined(OS_POSIX)
#include <stdio.h>
#include <sys/types.h>
#include <semaphore.h>
#include "base/file_descriptor_posix.h"
#include "base/files/file_util.h"
#include "base/files/scoped_file.h"
#if defined(OS_WIN)
#include "base/win/scoped_handle.h"
namespace base {
class FilePath;
// Options for creating a shared memory object.
struct BASE_EXPORT SharedMemoryCreateOptions {
#if defined(OS_MACOSX) && !defined(OS_IOS)
// The type of OS primitive that should back the SharedMemory object.
SharedMemoryHandle::Type type = SharedMemoryHandle::MACH;
#elif !defined(OS_FUCHSIA)
// 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 = nullptr;
// 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 = false;
#endif // defined(OS_MACOSX) && !defined(OS_IOS)
// Size of the shared memory object to be created.
// When opening an existing object, this has no effect.
size_t size = 0;
// If true, mappings might need to be made executable later.
bool executable = false;
// If true, the file can be shared read-only to a process.
bool share_read_only = false;
// Platform abstraction for shared memory.
// SharedMemory consumes a SharedMemoryHandle [potentially one that it created]
// to map a shared memory OS resource into the virtual address space of the
// current process.
class BASE_EXPORT 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 string16& name);
// 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
// GetReadOnlyHandle to drop permissions. TODO(jln,jyasskin): DCHECK
// that |read_only| matches the permissions of the handle.
SharedMemory(const SharedMemoryHandle& handle, bool read_only);
// Closes any open files.
// 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);
// 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();
// Duplicates The underlying OS primitive. Returns an invalid handle on
// failure. The caller is responsible for destroying the duplicated OS
// primitive.
static SharedMemoryHandle DuplicateHandle(const SharedMemoryHandle& handle);
#if defined(OS_POSIX) && !defined(OS_FUCHSIA)
// This method requires that the SharedMemoryHandle is backed by a POSIX fd.
static int GetFdFromSharedMemoryHandle(const SharedMemoryHandle& handle);
// 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);
#if (!defined(OS_MACOSX) || defined(OS_IOS)) && !defined(OS_FUCHSIA)
// 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);
#endif // !defined(OS_MACOSX) || defined(OS_IOS)
// 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);
// 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;
// Returns the underlying OS handle for this segment. The caller takes
// ownership of the handle and memory is unmapped. This is equivalent to
// duplicating the handle and then calling Unmap() and Close() on this object,
// without the overhead of duplicating the handle.
SharedMemoryHandle TakeHandle();
// Closes the open shared memory segment. The memory will remain mapped if
// it was previously mapped.
// It is safe to call Close repeatedly.
void Close();
// Returns a read-only handle to this shared memory region. The caller takes
// ownership of the handle. For POSIX handles, CHECK-fails if the region
// wasn't Created or Opened with share_read_only=true, which is required to
// make the handle read-only. When the handle is passed to the IPC subsystem,
// that takes ownership of the handle. As such, it's not valid to pass the
// sample handle to the IPC subsystem twice. Returns an invalid handle on
// failure.
SharedMemoryHandle GetReadOnlyHandle() const;
// Returns an ID for the mapped region. This is ID of the SharedMemoryHandle
// that was mapped. The ID is valid even after the SharedMemoryHandle is
// Closed, as long as the region is not unmapped.
const UnguessableToken& mapped_id() const { return mapped_id_; }
#if defined(OS_POSIX) && !defined(OS_NACL) && !defined(OS_ANDROID) && \
!defined(OS_FUCHSIA) && (!defined(OS_MACOSX) || defined(OS_IOS))
bool FilePathForMemoryName(const std::string& mem_name, FilePath* path);
#if defined(OS_WIN)
// If true indicates this came from an external source so needs extra checks
// before being mapped.
bool external_section_ = false;
string16 name_;
#elif !defined(OS_ANDROID) && !defined(OS_FUCHSIA)
// If valid, points to the same memory region as shm_, but with readonly
// permissions.
SharedMemoryHandle readonly_shm_;
#if defined(OS_MACOSX) && !defined(OS_IOS)
// The mechanism by which the memory is mapped. Only valid if |memory_| is not
// |nullptr|.
SharedMemoryHandle::Type mapped_memory_mechanism_ = SharedMemoryHandle::MACH;
// The OS primitive that backs the shared memory region.
SharedMemoryHandle shm_;
size_t mapped_size_ = 0;
void* memory_ = nullptr;
bool read_only_ = false;
size_t requested_size_ = 0;
base::UnguessableToken mapped_id_;
} // namespace base