• 9898287 (33/33) Oct 25 2019 Hi I want to find out what's causing my file writes to be so
• rikki cattermole (10/21) Oct 25 2019 I assume what you intended is:
• 9898287 (3/16) Oct 25 2019 Thank you for pointing that out.

9898287 <relay.public.adnan outlook.com> writes:

Hi I want to find out what's causing my file writes to be so 
slow. I'm setting up buffer and locking the file and writing them 
to the file.

$ cat d.d && ldc2 -O5  d.d && time ./d >> /dev/null
void main() {
     import std.stdio;
     stdout.setvbuf(4096);
     stdout.lock();

     foreach(i; 0 .. 900_000_000)
         writef("Hello, {}\n", i);
}
real    0m58.790s
user    0m58.545s
sys     0m0.232s

For comparison, I come from the Rust land and here's somewhat 
equivalent code which is consistently faster:

$ cat rust.rs && rustc -C opt-level=3 rust.rs && time ./rust >> 
/dev/null
use std::io::Write;

fn main() {
     let stdout = std::io::stdout();
     let lock = stdout.lock();
     let mut buf = std::io::BufWriter::new(lock);
     for i in 0 .. 900_000_000 {
         buf.write_fmt(format_args!(
             "Hello, {}\n", i
         )).unwrap();
     }
}

real    0m46.502s
user    0m46.263s
sys     0m0.228s

What am I missing?

rikki cattermole <rikki cattermole.co.nz> writes:

On 26/10/2019 2:27 PM, 9898287 wrote:
 Hi I want to find out what's causing my file writes to be so slow. I'm 
 setting up buffer and locking the file and writing them to the file.
 
 $ cat d.d && ldc2 -O5  d.d && time ./d >> /dev/null

You probably want -O3 not -O5.

 void main() {
      import std.stdio;
      stdout.setvbuf(4096);
      stdout.lock();
 
      foreach(i; 0 .. 900_000_000)
          writef("Hello, {}\n", i);

I assume what you intended is:
writeln("Hello, ", i);

Also for format functions in D you should prefer the templated variation 
as it provides compile time verification of arguments e.g.

writef!"Hello, {}\n%d"(i);

Please note that {} is not a format specifier.
printf style functions (which is what Phobos uses as the basis) for 
format specifiers begin with a percentage sign.

9898287 <relay.public.adnan outlook.com> writes:

On Saturday, 26 October 2019 at 02:42:04 UTC, rikki cattermole 
wrote:
 On 26/10/2019 2:27 PM, 9898287 wrote:
 [...]

 You probably want -O3 not -O5.

  [...]

 I assume what you intended is:
 writeln("Hello, ", i);

 Also for format functions in D you should prefer the templated 
 variation as it provides compile time verification of arguments 
 e.g.

 writef!"Hello, {}\n%d"(i);

 Please note that {} is not a format specifier.
 printf style functions (which is what Phobos uses as the basis) 
 for format specifiers begin with a percentage sign.

Thank you for pointing that out.