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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
// Copyright (c) 2006-2008 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_SHARED_MEMORY_H_
#define BASE_SHARED_MEMORY_H_
#include "build/build_config.h"
#if defined(OS_POSIX)
#include <sys/types.h>
#include <semaphore.h>
#include "base/file_descriptor_posix.h"
#endif
#include <string>
#include "base/basictypes.h"
#include "base/process.h"
namespace base {
// SharedMemoryHandle is a platform specific type which represents
// the underlying OS handle to a shared memory segment.
#if defined(OS_WIN)
typedef HANDLE SharedMemoryHandle;
typedef HANDLE SharedMemoryLock;
#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;
// On POSIX, the lock is implemented as a lockf() on the mapped file,
// so no additional member (or definition of SharedMemoryLock) is
// needed.
#endif
// Platform abstraction for shared memory. Provides a C++ wrapper
// around the OS primitive for a memory mapped file.
class SharedMemory {
public:
// Create a new SharedMemory object.
SharedMemory();
// Create a new SharedMemory object from an existing, open
// shared memory file.
SharedMemory(SharedMemoryHandle init_handle, bool read_only)
: SharedMemory() {
SetHandle(init_handle, read_only);
}
// Destructor. Will close any open files.
~SharedMemory();
// Initialize a new SharedMemory object from an existing, open
// shared memory file.
bool SetHandle(SharedMemoryHandle handle, bool read_only);
// 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);
// Return invalid handle (see comment above for exact definition).
static SharedMemoryHandle NULLHandle();
// Creates or opens a shared memory segment based on a name.
// If read_only is true, opens the memory as read-only.
// If open_existing is true, and the shared memory already exists,
// opens the existing shared memory and ignores the size parameter.
// If name is the empty string, use a unique name.
// Returns true on success, false on failure.
bool Create(const std::string& name, bool read_only, bool open_existing,
size_t size);
// Deletes resources associated with a shared memory segment based on name.
// Not all platforms require this call.
bool Delete(const std::wstring& name);
// Opens a shared memory segment based on a name.
// If read_only is true, opens for read-only access.
// If name is the empty string, use a unique name.
// Returns true on success, false on failure.
bool Open(const std::wstring& 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.
bool Map(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();
// Get the size of the opened shared memory backing file.
// Note: This size is only available to the creator of the
// shared memory, and not to those that opened shared memory
// created externally.
// Returns 0 if not opened or unknown.
size_t max_size() const { return max_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_; }
// Get access to 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)
// Return 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(bool unmap_view = true);
// Share 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 ouput parameter to receive
// the handle for use in the remote process.
// Returns true on success, false otherwise.
bool ShareToProcess(base::ProcessId target_pid,
SharedMemoryHandle* new_handle) {
return ShareToProcessCommon(target_pid, new_handle, false);
}
// 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(ProcessId target_pid,
SharedMemoryHandle* new_handle) {
return ShareToProcessCommon(target_pid, new_handle, true);
}
// Lock the shared memory.
// This is a cross-process lock which may be recursively
// locked by the same thread.
// TODO(port):
// WARNING: on POSIX the lock only works across processes, not
// across threads. 2 threads in the same process can both grab the
// lock at the same time. There are several solutions for this
// (futex, lockf+anon_semaphore) but none are both clean and common
// across Mac and Linux.
void Lock();
// Release the shared memory lock.
void Unlock();
private:
#if defined(OS_POSIX)
bool CreateOrOpen(const std::wstring &name, int posix_flags, size_t size);
bool FilenameForMemoryName(const std::wstring &memname,
std::wstring *filename);
void LockOrUnlockCommon(int function);
#endif
bool ShareToProcessCommon(ProcessId target_pid,
SharedMemoryHandle* new_handle,
bool close_self);
#if defined(OS_WIN)
std::wstring name_;
HANDLE mapped_file_;
#elif defined(OS_POSIX)
int mapped_file_;
ino_t inode_;
#endif
void* memory_;
bool read_only_;
size_t max_size_;
#if !defined(OS_POSIX)
SharedMemoryLock lock_;
#endif
DISALLOW_EVIL_CONSTRUCTORS(SharedMemory);
};
// A helper class that acquires the shared memory lock while
// the SharedMemoryAutoLock is in scope.
class SharedMemoryAutoLock {
public:
explicit SharedMemoryAutoLock(SharedMemory* shared_memory)
: shared_memory_(shared_memory) {
shared_memory_->Lock();
}
~SharedMemoryAutoLock() {
shared_memory_->Unlock();
}
private:
SharedMemory* shared_memory_;
DISALLOW_EVIL_CONSTRUCTORS(SharedMemoryAutoLock);
};
} // namespace base
#endif // BASE_SHARED_MEMORY_H_
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