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fix concurrency issue in part_file::export_file

This commit is contained in:
arvidn 2016-04-02 12:05:59 -04:00
parent 0020900a58
commit dff0e7b0cd
1 changed files with 29 additions and 8 deletions
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37
src/part_file.cpp
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@ -301,8 +301,10 @@ namespace libtorrent
void part_file::export_file(file& f, boost::int64_t offset, boost::int64_t size, error_code& ec)
{
mutex::scoped_lock l(m_mutex);
int piece = offset / m_piece_size;
int end = ((offset + size) + m_piece_size - 1) / m_piece_size;
int const end = ((offset + size) + m_piece_size - 1) / m_piece_size;
boost::scoped_array<char> buf;
@ -311,30 +313,49 @@ namespace libtorrent
for (; piece < end; ++piece)
{
boost::unordered_map<int, int>::iterator i = m_piece_map.find(piece);
int block_to_copy = (std::min)(m_piece_size - piece_offset, size);
int const block_to_copy = (std::min)(m_piece_size - piece_offset, size);
if (i != m_piece_map.end())
{
int const slot = i->second;
open_file(file::read_only, ec);
if (ec) return;
if (!buf) buf.reset(new char[m_piece_size]);
boost::int64_t slot_offset = boost::int64_t(m_header_size) + boost::int64_t(i->second) * m_piece_size;
file::iovec_t v = { buf.get(), size_t(block_to_copy) };
boost::int64_t const slot_offset = boost::int64_t(m_header_size)
+ boost::int64_t(slot) * m_piece_size;
// don't hold the lock during disk I/O
l.unlock();
file::iovec_t const v = { buf.get(), size_t(block_to_copy) };
int ret = m_file.readv(slot_offset + piece_offset, &v, 1, ec);
TORRENT_ASSERT(ec || ret == block_to_copy);
if (ec || ret != block_to_copy) return;
ret = f.writev(file_offset, &v, 1, ec);
TORRENT_ASSERT(ec || ret == block_to_copy);
if (ec || ret != block_to_copy) return;
// we're done with the disk I/O, grab the lock again to update
// the slot map
l.lock();
if (block_to_copy == m_piece_size)
{
m_free_slots.push_back(i->second);
m_piece_map.erase(i);
m_dirty_metadata = true;
// since we released the lock, it's technically possible that
// another thread removed this slot map entry, and invalidated
// our iterator. Now that we hold the lock again, perform
// another lookup to be sure.
boost::unordered_map<int, int>::iterator j = m_piece_map.find(piece);
if (j != m_piece_map.end())
{
// if the slot moved, that's really suspicious
TORRENT_ASSERT(j->second == slot);
m_free_slots.push_back(j->second);
m_piece_map.erase(j);
m_dirty_metadata = true;
}
}
}
file_offset += block_to_copy;