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No, C++ still isn’t cutting it

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 A recent blog put up asked “Does C++ aloof deserve its rotten rap?”

Whereas that title presumes the answer (despite all the pieces, a “rotten rap” implies that the judgement is undeserved), I gain C++’s reputation for making it very disturbing to operate security or memory safety or thread-safety remains richly deserved, even supposing or now no longer it’s gotten significantly higher over the years. I imply that: The c++-17 version of that program is years higher than it would had been with c++0x, and it let a careful programmer write a fine program.

The put up frail an easy multi-file note depend as an illustration:  Count all phrases in all “.txt” info in the present directory and all of its subdirectories, the set up phrases were defined as things matching the regexp “([a-z]{2,})” in a case-insensitive manner.

First, I’m going to plod via the example from that blog put up and establish some remaining bugs.  And then we are going to build up a (IMO) higher version in Rust that’s faster, safer, and more concise.  Let’s open with the body that processes the info and adds the counts to a hash desk:

A few things straight advance to mind when inspecting this code from a security perspective.  First, it makes disclose of a filesystem::recursive_directory_iterator to establish the info in the present directory, testing their forms and names earlier than processing them.  It then opens the file utilizing std::ifstream.

From the methodology I phrased this, you are perhaps already guessing that that is a TTCTTOU eror — time-to-take a look at-to-time-of-disclose. This scheme validates that the entry is a standard file, but then later opens it, and assumes that the of the take a look at holds. We can have to aloof search info from ourselves:

  • What happens if the file has been deleted between the directory list and the open?
  • What happens if the file has been replaced by, e.g., a pipe or diverse now no longer regular_file?

For the 2d case, or now no longer it’s somewhat clear that the program will strive to open it and operate on it; that is attributable to this truth a worm with appreciate to the intent of the programmer. Is it a mountainous worm in this context? Underneath no circumstances, but analogous bugs have resulted in serious security considerations.

For the first case, I wasn’t particular – and I wager many alternative C++ programmers don’t seem to be either. The solution is that the std::ifstream is gain, and can have to aloof merely behave in the same methodology as if EOF became once reached, but I wasn’t obvious about that till I googled it a lot and wrote a take a look at program to have a examine it. Unintended correctness is most practical than being contaminated, but we’re going to have to aloof strive for more in our packages.

Ultimately, the methodology or now no longer it’s written is now no longer finally very conducive to future multithreading. That’s wasn’t the purpose of the disclose, but I gain or now no longer it’s worth fascinated about as many stylish info processing packages resolve an evolutionary direction from single-threaded to multi-threaded. Constructs enjoy this invite threading bugs:

(1) It separates the computation of a gain dimension vary from utilizing that vary;  (2) it destructively modifies the word_array for no reason diverse than to manufacture it easy to print the first 10 gadgets.  And adding multithreading to things in C++ aloof remains significantly painful.

Listed below are some causes I’m coming to preserve Rust as a systems language. It’s now no longer remarkably shorter – the Python or shell version of all this can even be expressed in just a few traces of code!  However it undoubtedly’s a itsy-bitsy bit shorter, and or now no longer it’s more clear the set up corners had been reduce or errors nicely handled:

disclose as a minimal:: Result;

disclose lazysort::SortedBy;

disclose std::collections::HashMap;

disclose std::io::prelude::*;

fn scanfiles() -> Result<()> {

let mut wordcounts = HashMap:: new();

let phrases = regex::Regex:: new(r”([a-zA-Z]{2,})”)?;

for file in globwalk:: glob(“*.txt”)?

.filter_map(Result::okay)

.filter_map(|dirent| std::fs::File:: open(dirent.direction()).okay())

.filter(|file| {

file.metadata()

.and_then(|md| Okay(md.is_file()))

.unwrap_or(spurious)

})

{

let reader = std::io::BufReader:: new(file);

for line in reader.traces().filter_map(Result::okay) {

for note in phrases.captures_iter(&line) {

let w = note[0].to_lowercase();

*wordcounts.entry(w).or_insert(0) += 1;

}

}

}

let words_sorted = wordcounts.iter().sorted_by(|a, b| b.1.cmp(a.1));

for kv in words_sorted.resolve(10) {

println!(“{} {}”, kv.0, kv.1);

}

Okay(())

}

fn major() {

if let Err(e) = scanfiles() {

println!(“Error: One thing unexpected took situation: {:#?}”, e);

}

}


Okay, that’s 39 traces of code, but now no longer counting the Cargo.toml file, which is one other 4 of non-boilerplate (the four dependencies, which will doubtless be somewhat analogous to the #consist of traces in the C++ version, so will have to aloof be counted).

Comparatively shorter.  However what I enjoy about the Rust version is that there would possibly perhaps be a lot less guessing about the error handling.  Did the file fail to open?  We understand or now no longer it’s skipped, since the filter_map will discard that file if the of the open is now no longer okay.  We all know errors in globwalk or constructing the regex are handled, since the ? will motive the feature to advance abet an error in the event that they return an error.  The more functional .resolve(N) idiom is a chunk more fool-proof than the identical code in the C++ version, as we understand it returns early if there are fewer than N gadgets.

Whereas stylish C++ lets a careful programmer write a factual program, it aloof lets a less-careful programmer attain things in strategies that create errors. Rust has less of that: this would possibly perhaps nag you to quilt corner cases more carefully.

Rust would no longer fabricate it magically more straightforward to support a ways from that TTCTTOU arrangement back – it would had been right as easy to write the code utilizing std::fs::metadata(direction) in the same methodology it became once in the C++ version.  However it undoubtedly does toughen my self assurance that were that worm grunt, the code would have handled the “file would no longer exist” arrangement back. However it undoubtedly aloof would have opened a explicit file or directory with aplomb.

It’s moreover very easy to convert to a multithreaded program:  Factual turn the for x in … loop into a for_each, and disclose the Rayon crate .par_bridge() to motive the feature in for_each to be accomplished in parallel.

globwalk:: glob(“*.txt”)?

.filter_map(Result::okay)

.filter_map(|dirent| std::fs::File:: open(dirent.direction()).okay())

.filter(|file| {

file.metadata()

.and_then(|md| Okay(md.is_file()))

.unwrap_or(spurious)

})

.par_bridge()

.for_each(|file| {

Of route, that obtained’t bring collectively, because we’ve forgotten to disclose any locking on the hash desk into which we’re inserting counts:

error[E0596]: can now no longer borrow `wordcounts` as mutable, because it’s a ways a captured variable in a `Fn` closure

  –> src/major.rs: 25: 22

   |

25 |                     *wordcounts.entry(w).or_insert(0) += 1;

   |                      ^^^^^^^^^^ can now no longer borrow as mutable

So then we either swap it to a parallel hash desk, or we guard it with a mutex. I’m going to resolve the easy methodology of locking the desk earlier than utilizing it, and put only satisfactory optimization to manufacture it faster than the single-threaded version. On this case, I parse every line into lowercased-phrases, which I retailer in a vector, earlier than locking the hash desk and then bulk-inserting the highway’s worth of phrases:

disclose as a minimal:: Result;

disclose lazysort::SortedBy;

disclose rayon::prelude::*; // NEW

disclose std::collections::HashMap;

disclose std::io::prelude::*;

fn scanfiles() -> Result<()> {

let mut wordcounts = HashMap:: new();

let wordcounts_locked = std::sync::Mutex:: new(&mut wordcounts); // NEW

let phrases = regex::Regex:: new(r”([a-zA-Z]{2,})”)?;

globwalk:: glob(“*.txt”)?

.filter_map(Result::okay)

.filter_map(|dirent| std::fs::File:: open(dirent.direction()).okay())

.filter(|file| {

file.metadata()

.and_then(|md| Okay(md.is_file()))

.unwrap_or(spurious)

})

.par_bridge() // NEW

.for_each(|file| { // CHANGED

let reader = std::io::BufReader:: new(file);

for line in reader.traces().filter_map(Result::okay) {

let wordlist: Vec<String> = phrases // NEW DESIGN

.captures_iter(&line)

.draw(|w| w[0].to_lowercase())

.gain();

let mut wordcounts = wordcounts_locked.lock().unwrap();

for w in wordlist {

*wordcounts.entry(w).or_insert(0) += 1;

}

}

});

let words_sorted = wordcounts.iter().sorted_by(|a, b| b.1.cmp(a.1));

for kv in words_sorted.resolve(10) {

println!(“{} {}”, kv.1, kv.0);

}

Okay(())

}

fn major() {

if let Err(e) = scanfiles() {

println!(“Error: One thing unexpected took situation: {:#?}”, e);

}

}


No longer rotten – about ten traces of code modified to manufacture a usual parallel version of the code.

There are some advantages to the C++ version that judge the immaturity of the Rust standard library.  It became once able to without arrangement back disclose a partial_sort to reduce the amount of labor accomplished sorting by counts; I had to procure the lazysort crate, which is now no longer finally half of the usual library, which does the same thing.  

Each and each are swiftly, but curiously (and now no longer outdoors of my trip), the single-threaded Rust version is faster: With a sizzling cache, the C++ version (compiled with -O3)  takes 0.94 seconds to note depend 6 info on my MacBook pro, 5 of them runt and one among them a 2mb sample file with very repetitive text.  The Rust version (compiled with –open) takes about 0.2 seconds.

With a form of increased info, the parallel version can wordcount four 2mb sample info in 0.307 seconds utilizing a quad-core CPU – now no longer rather linear scaling, but now no longer rotten for a couple of minutes of tweaking.  The one-threaded C++ version, meanwhile, is caught taking about 3.55 seconds.

Despite its shorter dimension, the Rust version perhaps took me longer to write than the C++ version would have.  I had to spend more time determining what functions returned so I’m able to also handle their doable return forms, and had to spend a itsy-bitsy bit more time googling for things enjoy the filesystem metadata, perhaps because I’m more moderen to the language. However making it correct and making it parallel took less time, even supposing I’m less skilled in the language. I’m going to resolve that tradeoff in a form of what I attain.

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