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perf: cut down excess copying when downloading (#5907) 

* refactor: directly copy from socket to incoming payload

* refactor: directly process the incoming field

There is no need to copy the payload to a new buffer before processing.

`process_peer_message()` isn't going to return until it's done, and nothing else is going to mess with the incoming field while inside `process_peer_message()`.

* refactor: remove while loop

* add assert
This commit is contained in:
Yat Ho 2023-10-25 21:51:36 +08:00 committed by GitHub
parent f62f7427ed
commit 6e7fdef721
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1 changed files with 13 additions and 19 deletions
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32
libtransmission/peer-msgs.cc
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@ -1741,37 +1741,31 @@ ReadState canRead(tr_peerIo* io, void* vmsgs, size_t* piece)
// read <payload>
auto& current_payload = msgs->incoming.payload;
auto const full_payload_len = *current_message_len - sizeof(uint8_t /*message_type*/);
auto const full_payload_len = *current_message_len - sizeof(*current_message_type);
auto n_left = full_payload_len - std::size(current_payload);
while (n_left > 0U && io->read_buffer_size() > 0U)
{
auto buf = std::array<char, tr_block_info::BlockSize>{};
auto const n_this_pass = std::min({ n_left, io->read_buffer_size(), std::size(buf) });
io->read_bytes(std::data(buf), n_this_pass);
current_payload.add(std::data(buf), n_this_pass);
n_left -= n_this_pass;
logtrace(msgs, fmt::format("read {:d} payload bytes; {:d} left to go", n_this_pass, n_left));
}
auto const [buf, n_this_pass] = current_payload.reserve_space(std::min(n_left, io->read_buffer_size()));
TR_ASSERT(n_this_pass > 0U);
io->read_bytes(buf, n_this_pass);
current_payload.commit_space(n_this_pass);
n_left -= n_this_pass;
logtrace(msgs, fmt::format("read {:d} payload bytes; {:d} left to go", n_this_pass, n_left));
if (n_left > 0U)
{
return READ_LATER;
}
// The incoming message is now complete. Reset the peerMsgs' incoming
// field so it's ready to receive the next message, then process the
// current one with `process_peer_message()`.
// The incoming message is now complete. After processing the message
// with `process_peer_message()`, reset the peerMsgs' incoming
// field so it's ready to receive the next message.
auto const [read_state, n_piece_bytes_read] = process_peer_message(msgs, *current_message_type, current_payload);
*piece = n_piece_bytes_read;
current_message_len.reset();
auto const message_type = *current_message_type;
current_message_type.reset();
auto payload = MessageBuffer{};
payload.add(current_payload);
current_payload.clear();
auto const [read_state, n_piece_bytes_read] = process_peer_message(msgs, message_type, payload);
*piece = n_piece_bytes_read;
return read_state;
}