wtf/PageReservation.h

   1 /*
   2  * Copyright (C) 2010 Apple Inc. All rights reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef PageReservation_h
  27 #define PageReservation_h
  28
  29 #include <wtf/PageAllocation.h>
  30
  31 namespace WTF {
  32
  33 /*
  34     PageReservation
  35
  36     Like PageAllocation, the PageReservation class provides a cross-platform memory
  37     allocation interface, but with a set of capabilities more similar to that of
  38     VirtualAlloc than posix mmap.  PageReservation can be used to allocate virtual
  39     memory without committing physical memory pages using PageReservation::reserve.
  40     Following a call to reserve all memory in the region is in a decommited state,
  41     in which the memory should not be used (accessing the memory may cause a fault).
  42
  43     Before using memory it must be committed by calling commit, which is passed start
  44     and size values (both of which require system page size granularity).  One the
  45     committed memory is no longer needed 'decommit' may be called to return the
  46     memory to its devommitted state.  Commit should only be called on memory that is
  47     currently decommitted, and decommit should only be called on memory regions that
  48     are currently committed.  All memory should be decommited before the reservation
  49     is deallocated.  Values in memory may not be retained accross a pair of calls if
  50     the region of memory is decommitted and then committed again.
  51
  52     Memory protection should not be changed on decommitted memory, and if protection
  53     is changed on memory while it is committed it should be returned to the orignal
  54     protection before decommit is called.
  55 */
  56
  57 class PageReservation : private PageBlock {
  58 public:
  59     PageReservation()
  60         : m_committed(0)
  61         , m_writable(false)
  62         , m_executable(false)
  63     {
  64     }
  65
  66     using PageBlock::base;
  67     using PageBlock::size;
  68
  69 #ifndef __clang__
  70     using PageBlock::operator bool;
  71 #else
  72     // FIXME: This is a workaround for <rdar://problem/8876150>, wherein Clang incorrectly emits an access
  73     // control warning when a client tries to use operator bool exposed above via "using PageBlock::operator bool".
  74     operator bool() const { return PageBlock::operator bool(); }
  75 #endif
  76
  77     void commit(void* start, size_t size)
  78     {
  79         ASSERT(*this);
  80         ASSERT(isPageAligned(start));
  81         ASSERT(isPageAligned(size));
  82         ASSERT(contains(start, size));
  83
  84         m_committed += size;
  85         OSAllocator::commit(start, size, m_writable, m_executable);
  86     }
  87
  88     void decommit(void* start, size_t size)
  89     {
  90         ASSERT(*this);
  91         ASSERT(isPageAligned(start));
  92         ASSERT(isPageAligned(size));
  93         ASSERT(contains(start, size));
  94
  95         m_committed -= size;
  96         OSAllocator::decommit(start, size);
  97     }
  98
  99     size_t committed()
 100     {
 101         return m_committed;
 102     }
 103
 104     static PageReservation reserve(size_t size, OSAllocator::Usage usage = OSAllocator::UnknownUsage, bool writable = true, bool executable = false)
 105     {
 106         ASSERT(isPageAligned(size));
 107         return PageReservation(OSAllocator::reserveUncommitted(size, usage, writable, executable), size, writable, executable, false);
 108     }
 109
 110     static PageReservation reserveWithGuardPages(size_t size, OSAllocator::Usage usage = OSAllocator::UnknownUsage, bool writable = true, bool executable = false)
 111     {
 112         ASSERT(isPageAligned(size));
 113         return PageReservation(OSAllocator::reserveUncommitted(size + pageSize() * 2, usage, writable, executable, true), size, writable, executable, true);
 114     }
 115
 116     void deallocate()
 117     {
 118         ASSERT(!m_committed);
 119
 120         // Clear base & size before calling release; if this is *inside* allocation
 121         // then we won't be able to clear then after deallocating the memory.
 122         PageReservation tmp;
 123         std::swap(tmp, *this);
 124
 125         ASSERT(tmp);
 126         ASSERT(!*this);
 127
 128         OSAllocator::releaseDecommitted(tmp.base(), tmp.size());
 129     }
 130
 131 private:
 132     PageReservation(void* base, size_t size, bool writable, bool executable, bool hasGuardPages)
 133         : PageBlock(base, size, hasGuardPages)
 134         , m_committed(0)
 135         , m_writable(writable)
 136         , m_executable(executable)
 137     {
 138     }
 139
 140     size_t m_committed;
 141     bool m_writable;
 142     bool m_executable;
 143 };
 144
 145 }
 146
 147 using WTF::PageReservation;
 148
 149 #endif // PageReservation_h