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本文最后更新于 2024-07-24，文中内容可能已过时。
CS144 课程 Lab Assignment 中的 Checkpoint 1: stitching substrings into a byte stream
As part of the lab assignment, you will implement a TCP receiver: the module that receives datagrams and turns them into a reliable byte stream to be read from the socket by the application—just as your webget program read the byte stream from the webserver in Checkpoint 0
作为实验任务的一部分，你将实现一个 TCP 接收器：接收数据报并将其转化为可靠字节流的模块，以便应用程序从 socket 中读取–就像你的 webget 程序在 Checkpoint 0 中从网络服务器读取字节流一样。
在 Reassembler 类中添加下面这些字段:
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| std::deque<char> buffer_ {};
std::deque<bool> buf_enable_ {false};
uint64_t used_index_ {0};
uint64_t wcount_ {0};
bool fetch_last_ {false};
uint64_t max_length_ {0};
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对于 insert() 和 bytes_pending() 的实现:
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| void Reassembler::insert( uint64_t first_index, string data, bool is_last_substring )
{
const auto limit = std::min( data.size(), used_index_ + output_.writer().available_capacity() - first_index );
if (buffer_.size() < first_index + limit) {
buffer_.resize(first_index + limit);
buf_enable_.resize(first_index + limit);
}
for ( uint64_t i = 0; i < limit; ++i ) {
if (buf_enable_.at(first_index + i)) {
continue;
}
buffer_[first_index + i] = data.at(i);
buf_enable_[first_index + i] = true;
wcount_ += 1;
}
if ( is_last_substring ) {
fetch_last_ = true;
max_length_ = first_index + data.size();
}
for (; used_index_ < buf_enable_.size() && buf_enable_.at(used_index_); ++used_index_) {
output_.writer().push( std::string { buffer_.at( used_index_ ) } );
--wcount_;
}
if ( fetch_last_ && used_index_ == max_length_ ) {
buffer_.clear();
buf_enable_.clear();
output_.writer().close();
}
}
uint64_t Reassembler::bytes_pending() const
{
return wcount_;
}
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不过这样得不到太高的速度，我等下次尝试优化一下吧（逃
我就是 C++ 菜狗，优化也优化不了什么，换了个数据结构，一开始用 std::unordered_map<uint64_t, char>，查找很方便，但是插入擦除貌似就不是很行了，我选择用了 std::deque<char> 和 std::deque<bool> 来代替，需要一个 bool 类型的 std::deque<> 是因为我为了让插入字符的位置就是该字符实际的索引位置，直接 resize 放大 buffer 的大小，我想通过 std::deque<bool> buf_enable_ 标示一下哪个位是真实有效的，哪个是还没有值的。
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| $ cmake --build build -j`nproc` --target check1
Test project /home/zuos/codPjt/Cpp/minnow/build
Connected to MAKE jobserver
Start 1: compile with bug-checkers
1/17 Test #1: compile with bug-checkers ........ Passed 0.17 sec
Start 3: byte_stream_basics
2/17 Test #3: byte_stream_basics ............... Passed 0.01 sec
Start 4: byte_stream_capacity
3/17 Test #4: byte_stream_capacity ............. Passed 0.01 sec
Start 5: byte_stream_one_write
4/17 Test #5: byte_stream_one_write ............ Passed 0.01 sec
Start 6: byte_stream_two_writes
5/17 Test #6: byte_stream_two_writes ........... Passed 0.01 sec
Start 7: byte_stream_many_writes
6/17 Test #7: byte_stream_many_writes .......... Passed 0.04 sec
Start 8: byte_stream_stress_test
7/17 Test #8: byte_stream_stress_test .......... Passed 0.25 sec
Start 9: reassembler_single
8/17 Test #9: reassembler_single ............... Passed 0.01 sec
Start 10: reassembler_cap
9/17 Test #10: reassembler_cap .................. Passed 0.01 sec
Start 11: reassembler_seq
10/17 Test #11: reassembler_seq .................. Passed 0.01 sec
Start 12: reassembler_dup
11/17 Test #12: reassembler_dup .................. Passed 0.02 sec
Start 13: reassembler_holes
12/17 Test #13: reassembler_holes ................ Passed 0.01 sec
Start 14: reassembler_overlapping
13/17 Test #14: reassembler_overlapping .......... Passed 0.01 sec
Start 15: reassembler_win
14/17 Test #15: reassembler_win .................. Passed 5.40 sec
Start 37: compile with optimization
15/17 Test #37: compile with optimization ........ Passed 0.11 sec
Start 38: byte_stream_speed_test
ByteStream throughput: 0.59 Gbit/s
16/17 Test #38: byte_stream_speed_test ........... Passed 0.19 sec
Start 39: reassembler_speed_test
Reassembler throughput: 0.30 Gbit/s
17/17 Test #39: reassembler_speed_test ........... Passed 0.50 sec
100% tests passed, 0 tests failed out of 17
Total Test time (real) = 6.78 sec
Built target check1
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后来我换成 clang++ 编译，速度还有所提升
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| $ cmake --build build -j`nproc` --target check1
Test project /home/zuos/codPjt/Cpp/minnow/build
Connected to MAKE jobserver
Start 1: compile with bug-checkers
1/17 Test #1: compile with bug-checkers ........ Passed 0.19 sec
Start 3: byte_stream_basics
2/17 Test #3: byte_stream_basics ............... Passed 0.01 sec
Start 4: byte_stream_capacity
3/17 Test #4: byte_stream_capacity ............. Passed 0.02 sec
Start 5: byte_stream_one_write
4/17 Test #5: byte_stream_one_write ............ Passed 0.02 sec
Start 6: byte_stream_two_writes
5/17 Test #6: byte_stream_two_writes ........... Passed 0.01 sec
Start 7: byte_stream_many_writes
6/17 Test #7: byte_stream_many_writes .......... Passed 0.04 sec
Start 8: byte_stream_stress_test
7/17 Test #8: byte_stream_stress_test .......... Passed 0.20 sec
Start 9: reassembler_single
8/17 Test #9: reassembler_single ............... Passed 0.01 sec
Start 10: reassembler_cap
9/17 Test #10: reassembler_cap .................. Passed 0.01 sec
Start 11: reassembler_seq
10/17 Test #11: reassembler_seq .................. Passed 0.01 sec
Start 12: reassembler_dup
11/17 Test #12: reassembler_dup .................. Passed 0.02 sec
Start 13: reassembler_holes
12/17 Test #13: reassembler_holes ................ Passed 0.01 sec
Start 14: reassembler_overlapping
13/17 Test #14: reassembler_overlapping .......... Passed 0.01 sec
Start 15: reassembler_win
14/17 Test #15: reassembler_win .................. Passed 4.12 sec
Start 37: compile with optimization
15/17 Test #37: compile with optimization ........ Passed 0.10 sec
Start 38: byte_stream_speed_test
ByteStream throughput: 0.72 Gbit/s
16/17 Test #38: byte_stream_speed_test ........... Passed 0.16 sec
Start 39: reassembler_speed_test
Reassembler throughput: 0.35 Gbit/s
17/17 Test #39: reassembler_speed_test ........... Passed 0.43 sec
100% tests passed, 0 tests failed out of 17
Total Test time (real) = 5.36 sec
Built target check1
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