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94 lines
2.6 KiB
C++
94 lines
2.6 KiB
C++
// Copyright 2014 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_MAC_SCOPED_MACH_VM_H_
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#define BASE_MAC_SCOPED_MACH_VM_H_
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#include <mach/mach.h>
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#include <stddef.h>
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#include <algorithm>
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#include "base/base_export.h"
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#include "base/logging.h"
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#include "base/macros.h"
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// Use ScopedMachVM to supervise ownership of pages in the current process
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// through the Mach VM subsystem. Pages allocated with vm_allocate can be
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// released when exiting a scope with ScopedMachVM.
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//
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// The Mach VM subsystem operates on a page-by-page basis, and a single VM
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// allocation managed by a ScopedMachVM object may span multiple pages. As far
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// as Mach is concerned, allocated pages may be deallocated individually. This
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// is in contrast to higher-level allocators such as malloc, where the base
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// address of an allocation implies the size of an allocated block.
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// Consequently, it is not sufficient to just pass the base address of an
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// allocation to ScopedMachVM, it also needs to know the size of the
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// allocation. To avoid any confusion, both the base address and size must
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// be page-aligned.
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//
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// When dealing with Mach VM, base addresses will naturally be page-aligned,
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// but user-specified sizes may not be. If there's a concern that a size is
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// not page-aligned, use the mach_vm_round_page macro to correct it.
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//
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// Example:
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//
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// vm_address_t address = 0;
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// vm_size_t size = 12345; // This requested size is not page-aligned.
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// kern_return_t kr =
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// vm_allocate(mach_task_self(), &address, size, VM_FLAGS_ANYWHERE);
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// if (kr != KERN_SUCCESS) {
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// return false;
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// }
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// ScopedMachVM vm_owner(address, mach_vm_round_page(size));
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namespace base {
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namespace mac {
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class BASE_EXPORT ScopedMachVM {
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public:
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explicit ScopedMachVM(vm_address_t address = 0, vm_size_t size = 0)
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: address_(address), size_(size) {
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DCHECK_EQ(address % PAGE_SIZE, 0u);
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DCHECK_EQ(size % PAGE_SIZE, 0u);
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}
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~ScopedMachVM() {
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if (size_) {
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vm_deallocate(mach_task_self(), address_, size_);
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}
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}
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void reset(vm_address_t address = 0, vm_size_t size = 0);
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vm_address_t address() const {
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return address_;
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}
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vm_size_t size() const {
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return size_;
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}
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void swap(ScopedMachVM& that) {
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std::swap(address_, that.address_);
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std::swap(size_, that.size_);
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}
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void release() {
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address_ = 0;
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size_ = 0;
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}
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private:
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vm_address_t address_;
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vm_size_t size_;
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DISALLOW_COPY_AND_ASSIGN(ScopedMachVM);
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};
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} // namespace mac
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} // namespace base
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#endif // BASE_MAC_SCOPED_MACH_VM_H_
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