storage_interface阅读解释

Question

我已经在libtorrent中实现了自定义存储接口，如此处的帮助部分所述。

storage_interface工作正常，尽管我不知道为什么readv下载种子时只随机调用。在我看来，每次我在piece_finished_alert中调用handle->read_piece时，都应该调用覆盖的虚拟函数readv。它应该为read_piece_alert阅读这篇文章吗？

缓冲区以read_piece_alert形式提供，而不会在readv中收到通知。

所以问题是为什么它只被随机调用，为什么它不被调用read_piece()调用？我的storage_interface可能是错的吗？

代码如下所示：

struct temp_storage : storage_interface
{
virtual int readv(file::iovec_t const* bufs, int num_bufs
, int piece, int offset, int flags, storage_error& ec)
{
// Only called on random pieces while downloading a larger torrent 
std::map<int, std::vector<char> >::const_iterator i = m_file_data.find(piece);
if (i == m_file_data.end()) return 0;
int available = i->second.size() - offset;
if (available <= 0) return 0;
if (available > num_bufs) available = num_bufs;
memcpy(&bufs, &i->second[offset], available); 
return available;
}
virtual int writev(file::iovec_t const* bufs, int num_bufs
, int piece, int offset, int flags, storage_error& ec)
{
std::vector<char>& data = m_file_data[piece];
if (data.size() < offset + num_bufs) data.resize(offset + num_bufs);
std::memcpy(&data[offset], bufs, num_bufs);
return num_bufs;
}
virtual bool has_any_file(storage_error& ec) { return false; }
virtual ... 
virtual ...
}

初始化为

storage_interface* temp_storage_constructor(storage_params const& params)
{
printf("NEW INTERFACEn");
return new temp_storage(*params.files);
}
p.storage = &temp_storage_constructor;

下面的函数设置警报并调用每个已完成作品的read_piece。

while(true) {
std::vector<alert*> alerts;
s.pop_alerts(&alerts);
for (alert* i : alerts)
{
switch (i->type()) {
case read_piece_alert::alert_type:
{
read_piece_alert* p = (read_piece_alert*)i;
if (p->ec) {
// read_piece failed
break;
}
// piece buffer, size is provided without readv
// notification after invoking read_piece in piece_finished_alert
break;
}
case piece_finished_alert::alert_type: {
piece_finished_alert* p = (piece_finished_alert*)i;               
p->handle.read_piece(p->piece_index);
// Once the piece is finished, we read it to obtain the buffer in read_piece_alert.  
break;
}
default:
break;
}
}
Sleep(100);
}

Answer 1

我会回答我自己的问题。正如 Arvid 在评论中所说：由于缓存，没有调用readv。将settings_pack::use_read_cache设置为 false 将始终调用readv。