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Why RawStream
contains an Iterator
of Vec<u8>
instead of std::io::Read
?
#7017
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Hi, I looked at this a bit and I'm not sure why we did it that way, sorry! If you want to try adding a new custom
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stormasm
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May 16, 2024
# Description This PR introduces a `ByteStream` type which is a `Read`-able stream of bytes. Internally, it has an enum over three different byte stream sources: ```rust pub enum ByteStreamSource { Read(Box<dyn Read + Send + 'static>), File(File), Child(ChildProcess), } ``` This is in comparison to the current `RawStream` type, which is an `Iterator<Item = Vec<u8>>` and has to allocate for each read chunk. Currently, `PipelineData::ExternalStream` serves a weird dual role where it is either external command output or a wrapper around `RawStream`. `ByteStream` makes this distinction more clear (via `ByteStreamSource`) and replaces `PipelineData::ExternalStream` in this PR: ```rust pub enum PipelineData { Empty, Value(Value, Option<PipelineMetadata>), ListStream(ListStream, Option<PipelineMetadata>), ByteStream(ByteStream, Option<PipelineMetadata>), } ``` The PR is relatively large, but a decent amount of it is just repetitive changes. This PR fixes #7017, fixes #10763, and fixes #12369. This PR also improves performance when piping external commands. Nushell should, in most cases, have competitive pipeline throughput compared to, e.g., bash. | Command | Before (MB/s) | After (MB/s) | Bash (MB/s) | | -------------------------------------------------- | -------------:| ------------:| -----------:| | `throughput \| rg 'x'` | 3059 | 3744 | 3739 | | `throughput \| nu --testbin relay o> /dev/null` | 3508 | 8087 | 8136 | # User-Facing Changes - This is a breaking change for the plugin communication protocol, because the `ExternalStreamInfo` was replaced with `ByteStreamInfo`. Plugins now only have to deal with a single input stream, as opposed to the previous three streams: stdout, stderr, and exit code. - The output of `describe` has been changed for external/byte streams. - Temporary breaking change: `bytes starts-with` no longer works with byte streams. This is to keep the PR smaller, and `bytes ends-with` already does not work on byte streams. - If a process core dumped, then instead of having a `Value::Error` in the `exit_code` column of the output returned from `complete`, it now is a `Value::Int` with the negation of the signal number. # After Submitting - Update docs and book as necessary - Release notes (e.g., plugin protocol changes) - Adapt/convert commands to work with byte streams (high priority is `str length`, `bytes starts-with`, and maybe `bytes ends-with`). - Refactor the `tee` code, Devyn has already done some work on this. --------- Co-authored-by: Devyn Cairns <devyn.cairns@gmail.com>
FilipAndersson245
pushed a commit
to FilipAndersson245/nushell
that referenced
this issue
May 18, 2024
# Description This PR introduces a `ByteStream` type which is a `Read`-able stream of bytes. Internally, it has an enum over three different byte stream sources: ```rust pub enum ByteStreamSource { Read(Box<dyn Read + Send + 'static>), File(File), Child(ChildProcess), } ``` This is in comparison to the current `RawStream` type, which is an `Iterator<Item = Vec<u8>>` and has to allocate for each read chunk. Currently, `PipelineData::ExternalStream` serves a weird dual role where it is either external command output or a wrapper around `RawStream`. `ByteStream` makes this distinction more clear (via `ByteStreamSource`) and replaces `PipelineData::ExternalStream` in this PR: ```rust pub enum PipelineData { Empty, Value(Value, Option<PipelineMetadata>), ListStream(ListStream, Option<PipelineMetadata>), ByteStream(ByteStream, Option<PipelineMetadata>), } ``` The PR is relatively large, but a decent amount of it is just repetitive changes. This PR fixes nushell#7017, fixes nushell#10763, and fixes nushell#12369. This PR also improves performance when piping external commands. Nushell should, in most cases, have competitive pipeline throughput compared to, e.g., bash. | Command | Before (MB/s) | After (MB/s) | Bash (MB/s) | | -------------------------------------------------- | -------------:| ------------:| -----------:| | `throughput \| rg 'x'` | 3059 | 3744 | 3739 | | `throughput \| nu --testbin relay o> /dev/null` | 3508 | 8087 | 8136 | # User-Facing Changes - This is a breaking change for the plugin communication protocol, because the `ExternalStreamInfo` was replaced with `ByteStreamInfo`. Plugins now only have to deal with a single input stream, as opposed to the previous three streams: stdout, stderr, and exit code. - The output of `describe` has been changed for external/byte streams. - Temporary breaking change: `bytes starts-with` no longer works with byte streams. This is to keep the PR smaller, and `bytes ends-with` already does not work on byte streams. - If a process core dumped, then instead of having a `Value::Error` in the `exit_code` column of the output returned from `complete`, it now is a `Value::Int` with the negation of the signal number. # After Submitting - Update docs and book as necessary - Release notes (e.g., plugin protocol changes) - Adapt/convert commands to work with byte streams (high priority is `str length`, `bytes starts-with`, and maybe `bytes ends-with`). - Refactor the `tee` code, Devyn has already done some work on this. --------- Co-authored-by: Devyn Cairns <devyn.cairns@gmail.com>
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Question
RawStream
is an iterator of heap-allocated chunks of bytes as opposed tostd::io::Read
which may harm performance in some cases. The only reason that comes to my mind is having a different error type but that could've been implemented by having a customRead
trait that's a copy ofstd::io::Read
except for error bytes.Is there any other reason I don' see? If not how hard would it be to refactor it?
Additional context and details
I started working on optimizing json objects parsing to not collect the whole stream into string as mentioned in #6979 (comment) and assumed it implements
Read
which is not the case. I even implemented a bunch of optimizations aiming at significantly reducing heap allocations. 🤦♂️ I'm now wondering how to proceed.The text was updated successfully, but these errors were encountered: