The Detroit Post
Thursday, 21 October, 2021

Rust Fastest Way To Read File

author
Bob Roberts
• Friday, 25 December, 2020
• 8 min read

In fact, it meant that the fastest one token was suddenly faster than my SCC for almost all tests. In addition, a new project polyglot written in a language I have never heard of ATS popped up which is also now faster than my Go program for any repository when running on a machine with less than 8 cores.

Contents

I looked a little further into SCC to determine if I could improve the performance at all and came away unconvinced. During this process I tried running it compared to token on a 32 core machine with 50 copies of the Linux kernel.

I played around with how SCC worked internally and I couldn’t come up with any way to speed it up. Seeing as I wanted to learn Rust anyway it seemed like a good idea to attempt to port SCC into Rust, and learn if SCC had been faster if so.

It's certainly a very easy language to get started with, has a fast feedback loop and generally I don’t write much code that needs such a level performance. When you are working with HTTP endpoints what's a few milliseconds between friends.

I was not going to do this with any parallel code as I wanted to see how fast Rust was compared to Go on the core loop. This would be the very least amount required in order to start porting SCC across.

My goal was to a Rust version to run at the same speed. My first attempt to do the above in Rust I used the Walk Dir crate used in rip grep and as with the Go version didn’t bother with any error checking.

Looking again at the Rust docs its possible to read the file into a Vector from the start. Since the Go code actually reads the whole file into memory this seemed like a likely candidate as to the difference.

In fact what is actually happening in the above Rust is that it is performing a miscall to fetch every byte. Just to be sure my laptop was not infusing the result I created a Digital Ocean instance and tried it out on a copy of the Linux kernel.

Wondering if perhaps the first version was faster on Linux I copied that up and ran it. The changes are to set up the buffer Vector outside the core loop and clear it and reload each run.

Trying it out on a much larger repository, which is a fresh checkout of the Linux kernel. That said Rust does push the happy parts of my brain in a way that Python does.

The last line write_all function will write bytes in newly created file. If any of the operations fail, the expect() function returns an error message.

The following program reads the contents in a file data.txt and prints it to the console. An absolute or relative path to the file is passed to the open() function as a parameter.

The open() function throws an exception if the file does not exist, or if it is not accessible for whatever reason. The expect() function returns a custom message in case an error occurs.

Two command line arguments are passed while executing the file Note : this answer is about PRE Rust 1.0 and thus outdated.

The file descriptor will be closed automatically on the exit of the scope, so there is no f.close() method. A reference to an open file on the file system.

An instance of a File can be read and/or written depending on what options it was opened with. Errors detected on closing are ignored by the implementation of Drop.

Additionally, many operating systems allow concurrent modification of files by different processes. Attempts to open a file in read -only mode.

This function will return an error if path does not already exist. This function will create a file if it does not exist, and will truncate it if it does.

This function returns a new Operations object that you can use to open or create a file with specific options if open() or create() are not appropriate. It is equivalent to Operations::new() but allows you to write more readable code.

This function will attempt to ensure that all in-memory data reaches the file system before returning. This can be used to handle errors that would otherwise only be caught when the File is closed.

Dropping a file will ignore errors in synchronizing this in-memory data. This function is similar to sync_all, except that it may not synchronize file metadata to the file system.

This is intended for use cases that must synchronize content, but don't need the metadata on disk. The goal of this method is to reduce disk operations.

Note that some platforms may simply implement this in terms of sync_all. If it is greater than the current file's size, then the file will be extended to size and have all the intermediate data filled in with 0s.

This function will return an error if the file is not opened for writing. Also, std::Io::ErrorKind::Invaliding will be returned if the desired length would cause an overflow due to the implementation specifics.

Note that this method alters the content of the underlying file, even though it takes self rather than smut self. Queries metadata about the underlying file.

Changes the permissions on the underlying file. This function will return an error if the user lacks permission change attributes on the underlying file.

Note that this method alters the permissions of the underlying file, even though it takes self rather than smut self. Determines if this Read her can work with buffers of uninitialized memory.

Read all bytes until EOF in this source, placing them into BUF. Read all bytes until EOF in this source, appending them to BUF.

Fn take (self, limit: u64) Take where Self: Sized, Creates an adaptor which will read at most limit bytes from it. Determines if this Read her can work with buffers of uninitialized memory.

Read all bytes until EOF in this source, placing them into BUF. Read all bytes until EOF in this source, appending them to BUF.

Fn take (self, limit: u64) Take where Self: Sized, Creates an adaptor which will read at most limit bytes from it. Write a buffer into this writer, returning how many bytes were written.

Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Attempts to write an entire buffer into this writer.

Attempts to write multiple buffers into this writer. Writes a formatted string into this writer, returning any error encountered.

Creates a “by reference” adaptor for this instance of Write. Write a buffer into this writer, returning how many bytes were written.

Flush this output stream, ensuring that all intermediately buffered contents reach their destination. Attempts to write an entire buffer into this writer.

Attempts to write multiple buffers into this writer. Writes a formatted string into this writer, returning any error encountered.

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