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// 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 <string>
#include "base/basictypes.h"
#include "base/process.h"
// 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)
#include <semaphore.h>
typedef int SharedMemoryHandle;
typedef sem_t* SharedMemoryLock;
#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 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);
// Destructor. Will close any open files.
~SharedMemory();
// 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.
// Returns true on success, false on failure.
bool Create(const std::wstring& name, bool read_only, bool open_existing,
size_t size);
// 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::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 { return mapped_file_; }
// Closes the open shared memory segment.
// It is safe to call Close repeatedly.
void Close();
// 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(ProcessHandle process,
SharedMemoryHandle* new_handle) {
return ShareToProcessCommon(process, new_handle, false);
}
// Logically equivalent to:
// bool ok = ShareToProcess(process, new_handle);
// Close();
// return ok;
bool GiveToProcess(ProcessHandle process,
SharedMemoryHandle* new_handle) {
return ShareToProcessCommon(process, new_handle, true);
}
// Lock the shared memory.
// This is a cross-process lock which may be recursively
// locked by the same thread.
void Lock();
// Release the shared memory lock.
void Unlock();
private:
#if defined(OS_POSIX)
bool CreateOrOpen(const std::wstring &name, int posix_flags);
#endif
bool ShareToProcessCommon(ProcessHandle process,
SharedMemoryHandle* new_handle,
bool close_self);
std::wstring name_;
SharedMemoryHandle mapped_file_;
void* memory_;
bool read_only_;
size_t max_size_;
SharedMemoryLock lock_;
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);
};
#endif // BASE_SHARED_MEMORY_H_
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