void file_storage::optimize(int pad_file_limit)
{
// the main purpuse of padding is to optimize disk
// I/O. This is a conservative memory page size assumption
int alignment = 8*1024;
// it doesn't make any sense to pad files that
// are smaller than one piece
if (pad_file_limit >= 0 && pad_file_limit < alignment)
pad_file_limit = alignment;
size_type off = 0;
int padding_file = 0;
for (std::vector<internal_file_entry>::iterator i = m_files.begin();
i != m_files.end(); ++i)
{
if ((off & (alignment-1)) == 0)
{
// this file position is aligned, pick the largest
// available file to put here
std::vector<internal_file_entry>::iterator best_match
= std::max_element(i, m_files.end()
, &compare_file_entry_size);
if (best_match != i)
{
int index = file_index(*best_match);
int cur_index = file_index(*i);
reorder_file(index, cur_index);
i = m_files.begin() + cur_index;
}
}
else if (pad_file_limit >= 0
&& (off & (alignment-1)) != 0
&& i->size > pad_file_limit
&& i->pad_file == false)
{
// if we have pad files enabled, and this file is
// not piece-aligned and the file size exceeds the
// limit, and it's not a padding file itself.
// so add a padding file in front of it
int pad_size = alignment - (off & (alignment-1));
// find the largest file that fits in pad_size
std::vector<internal_file_entry>::iterator best_match = m_files.end();
for (std::vector<internal_file_entry>::iterator j = i+1; j < m_files.end(); ++j)
{
if (j->size > pad_size) continue;
if (best_match == m_files.end() || j->size > best_match->size)
best_match = j;
}
if (best_match != m_files.end())
{
// we found one
// We cannot have found i, because i->size > pad_file_limit
// which is forced to be no less than alignment. We only
// look for files <= pad_size, which never is greater than
// alignment
TORRENT_ASSERT(best_match != i);
int index = file_index(*best_match);
int cur_index = file_index(*i);
reorder_file(index, cur_index);
i = m_files.begin() + cur_index;
i->offset = off;
off += i->size;
continue;
}
// we could not find a file that fits in pad_size
// add a padding file
// note that i will be set to point to the
// new pad file. Once we're done adding it, we need
// to increment i to point to the current file again
internal_file_entry e;
i = m_files.insert(i, e);
i->size = pad_size;
i->offset = off;
char name[30];
snprintf(name, sizeof(name), ".____padding_file/%d", padding_file);
std::string path = combine_path(m_name, name);
i->set_name(path.c_str());
i->pad_file = true;
off += pad_size;
++padding_file;
// skip the pad file we just added and point
// at the current file again
++i;
}
i->offset = off;
off += i->size;
}
m_total_size = off;
}
void file_storage::optimize(int pad_file_limit, int alignment)
{
// it doesn't make any sense to pad files that
// are smaller than one block
if (pad_file_limit >= 0 && pad_file_limit < 0x4000)
pad_file_limit = 0x4000;
// also, it doesn't make any sense to pad files
// that are smaller than the alignment, since they
// won't get aligned anyway; they are used as padding
if (pad_file_limit >= 0 && pad_file_limit < alignment)
pad_file_limit = alignment;
size_type off = 0;
int padding_file = 0;
for (std::vector<internal_file_entry>::iterator i = m_files.begin();
i != m_files.end(); ++i)
{
if ((off & (alignment-1)) == 0)
{
// this file position is aligned, pick the largest
// available file to put here
std::vector<internal_file_entry>::iterator best_match
= std::max_element(i, m_files.end()
, &compare_file_entry_size);
if (best_match != i)
{
int index = file_index(*best_match);
int cur_index = file_index(*i);
reorder_file(index, cur_index);
i = m_files.begin() + cur_index;
}
}
else if (pad_file_limit >= 0
&& i->size > pad_file_limit
&& i->pad_file == false)
{
// if we have pad files enabled, and this file is
// not piece-aligned and the file size exceeds the
// limit, and it's not a padding file itself.
// so add a padding file in front of it
int pad_size = alignment - (off & (alignment-1));
// find the largest file that fits in pad_size
std::vector<internal_file_entry>::iterator best_match = m_files.end();
for (std::vector<internal_file_entry>::iterator j = i+1; j < m_files.end(); ++j)
{
if (j->size > pad_size) continue;
if (best_match == m_files.end() || j->size > best_match->size)
best_match = j;
}
if (best_match != m_files.end())
{
// we found one
// We cannot have found i, because i->size > pad_file_limit
// which is forced to be no less than alignment. We only
// look for files <= pad_size, which never is greater than
// alignment
TORRENT_ASSERT(best_match != i);
int index = file_index(*best_match);
int cur_index = file_index(*i);
reorder_file(index, cur_index);
i = m_files.begin() + cur_index;
i->offset = off;
off += i->size;
continue;
}
// we could not find a file that fits in pad_size
// add a padding file
// note that i will be set to point to the
// new pad file. Once we're done adding it, we need
// to increment i to point to the current file again
// first add the pad file to the end of the file list
// then swap it in place. This minimizes the amount
// of copying of internal_file_entry, which is somewhat
// expensive (until we have move semantics)
int cur_index = file_index(*i);
int index = m_files.size();
m_files.push_back(internal_file_entry());
internal_file_entry& e = m_files.back();
// i may have been invalidated, refresh it
i = m_files.begin() + cur_index;
e.size = pad_size;
e.offset = off;
char name[30];
snprintf(name, sizeof(name), ".____padding_file/%d", padding_file);
std::string path = combine_path(m_name, name);
e.set_name(path.c_str());
e.pad_file = true;
off += pad_size;
++padding_file;
if (!m_mtime.empty()) m_mtime.resize(index + 1, 0);
if (!m_file_hashes.empty()) m_file_hashes.resize(index + 1, NULL);
if (!m_file_base.empty()) m_file_base.resize(index + 1, 0);
reorder_file(index, cur_index);
TORRENT_ASSERT((off & (alignment-1)) == 0);
continue;
}
i->offset = off;
off += i->size;
}
m_total_size = off;
}
