libcruft-util/memory/buffer/paged.cpp

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/*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* Copyright 2015 Danny Robson <danny@nerdcruft.net>
*/
#include "paged.hpp"
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#include "../system.hpp"
#include "../../except.hpp"
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#include "../../maths.hpp"
#include "../../pointer.hpp"
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#include "../../cast.hpp"
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#include <sys/mman.h>
using util::memory::buffer::paged;
///////////////////////////////////////////////////////////////////////////////
paged::paged (size_t bytes, size_t _window):
m_window (round_to (_window, pagesize ()))
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{
// reserve the address region with no access permissions
m_begin = reinterpret_cast<char*> (
mmap (nullptr, bytes, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0)
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);
if (m_begin == MAP_FAILED)
errno_error::throw_code ();
// remap the initial window with read/write permissions
m_cursor = m_begin + round_to (min (m_window, bytes), pagesize ());
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if (MAP_FAILED == mmap (m_begin,
m_cursor - m_begin,
PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0))
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errno_error::throw_code ();
// record the nominal end address
m_end = m_begin + round_to (bytes, pagesize ());
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}
//-----------------------------------------------------------------------------
paged::~paged ()
{
// ignore errors in production; we don't want to double throw.
auto res = munmap (m_begin, m_end - m_begin);
(void)res;
CHECK_ZERO (res);
}
///////////////////////////////////////////////////////////////////////////////
char*
paged::begin (void)&
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{
return m_begin;
}
//-----------------------------------------------------------------------------
char*
paged::end (void)&
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{
return m_end;
}
///////////////////////////////////////////////////////////////////////////////
void
paged::access (char *cursor)
{
if (cursor < m_cursor)
release (cursor);
else
commit (cursor);
}
//-----------------------------------------------------------------------------
void
paged::commit (char *cursor)
{
// bail if it's already mapped
if (cursor <= m_cursor)
return;
if (cursor > m_end || cursor < m_begin)
throw std::out_of_range ("invalid commit cursor");
// bump the request up to page aligned and tack on a little to amortize
// syscall overheads
cursor = align (cursor, pagesize ()) + m_window;
cursor = min (cursor, m_end);
if (MAP_FAILED == mmap (m_cursor,
cursor - m_cursor,
PROT_READ | PROT_WRITE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0))
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errno_error::throw_code ();
m_cursor = cursor;
}
//-----------------------------------------------------------------------------
void
paged::release (char *desired)
{
if (desired > m_end || desired < m_begin)
throw std::out_of_range ("invalid release cursor");
align (desired, pagesize ());
// bail if the region is alread unmapped, or if it's not sufficiently
// behind the current cursor.
if (desired >= m_cursor || sign_cast<size_t> (m_cursor - desired) < m_window)
return;
desired += m_window;
if (MAP_FAILED == mmap (desired,
m_end - desired,
PROT_NONE,
MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS,
-1, 0))
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errno_error::throw_code ();
m_cursor = desired;
}
///////////////////////////////////////////////////////////////////////////////
size_t
paged::size (void) const
{
return m_cursor - m_begin;
}
//-----------------------------------------------------------------------------
size_t
paged::capacity (void) const
{
return m_end - m_begin;
}
//-----------------------------------------------------------------------------
size_t
paged::window (void) const
{
return m_window;
}