rhg: Don’t compare ambiguous files one byte at a time
Even though the use of `BufReader` reduces the number of syscalls to read
the file from disk, `.bytes()` yields a separate `Result` for every byte.
Creating those results and dispatching on them is most likely costly.
Instead, this commit opts for simplicity by reading the entire file into memory
and comparing a single pair of byte strings. Note that memory already needs to
contain the entire previous contents of the file, as read from the filelog.
So with an extremely large file this doubles memory use but does not make it
grow by orders of magnitude.
At first I wrote code that still avoids reading the entire file into memory
and compares one buffer at a time with `BufReader`. Find this code below for
posterity. However its correctness is subtle. I ended up preferring the
simplicity of the obviously-correct single comparison.
```rust
let mut reader = BufReader::new(fobj);
let mut expected = &contents_in_p1[..];
loop {
let buf = reader.fill_buf().when_reading_file(&fs_path)?;
if buf.is_empty() {
// Found EOF
return Ok(expected.is_empty());
} else if let Some(rest) = expected.drop_prefix(buf) {
// What we read so far matches the expected content, continue reading
let buf_len = buf.len();
reader.consume(buf_len);
expected = rest
} else {
// Found different content
return Ok(false);
}
}
```
Differential Revision: https://phab.mercurial-scm.org/D11412
# memory.py - track memory usage
#
# Copyright 2009 Olivia Mackall <olivia@selenic.com> and others
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
'''helper extension to measure memory usage
Reads current and peak memory usage from ``/proc/self/status`` and
prints it to ``stderr`` on exit.
'''
from __future__ import absolute_import
def memusage(ui):
"""Report memory usage of the current process."""
result = {'peak': 0, 'rss': 0}
with open('/proc/self/status', 'r') as status:
# This will only work on systems with a /proc file system
# (like Linux).
for line in status:
parts = line.split()
key = parts[0][2:-1].lower()
if key in result:
result[key] = int(parts[1])
ui.write_err(
", ".join(
["%s: %.1f MiB" % (k, v / 1024.0) for k, v in result.iteritems()]
)
+ "\n"
)
def extsetup(ui):
ui.atexit(memusage, ui)