This updates encoding_rs, crossbeam-utils and crossbeam-channel. This
serves two purposes. The encoding_rs update fixes a compilation failure
on the latest nightly. The crossbeam updates are good sense and to
reduce duplicate dependencies such as cfg-if. (Although, we note that
the log crate still pulls in cfg-if 0.1, so ripgrep has a duplicate
dependency there for now. But it's very small.)
Fixes#1721, Closes#1705
This replaces the use of channels in the parallel directory traversal
with a simple stack. The primary motivation for this change is to reduce
peak memory usage. In particular, when using a channel (which is a
queue), we wind up visiting files in a breadth first fashion. Using a
stack switches us to a depth first traversal. While there are no real
intrinsic differences, depth first traversal generally tends to use less
memory because directory trees are more commonly wide than they are
deep.
In particular, the queue/stack size itself is not the only concern. In
one recent case documented in #1550, a user wanted to search all Rust
crates. The directory structure was shallow but extremely wide, with a
single directory containing all crates. This in turn results is in
descending into each of those directories and building a gitignore
matcher for each (since most crates have `.gitignore` files) before ever
searching a single file. This means that ripgrep has all such matchers
in memory simultaneously, which winds up using quite a bit of memory.
In a depth first traversal, peak memory usage is much lower because
gitignore matches are built and discarded more quickly. In the case of
searching all crates, the peak memory usage decrease is dramatic. On my
system, it shrinks by an order magnitude, from almost 1GB to 50MB. The
decline in peak memory usage is consistent across other use cases as
well, but is typically more modest. For example, searching the Linux
repo has a 50% decrease in peak memory usage and searching the Chromium
repo has a 25% decrease in peak memory usage.
Search times generally remain unchanged, although some ad hoc benchmarks
that I typically run have gotten a bit slower. As far as I can tell,
this appears to be result of scheduling changes. Namely, the depth first
traversal seems to result in searching some very large files towards the
end of the search, which reduces the effectiveness of parallelism and
makes the overall search take longer. This seems to suggest that a stack
isn't optimal. It would instead perhaps be better to prioritize
searching larger files first, but it's not quite clear how to do this
without introducing more overhead (getting the file size for each file
requires a stat call).
Fixes#1550
The top-level listing was just getting a bit too long for my taste. So
put all of the code in one directory and shrink the large top-level mess
to a small top-level mess.
NOTE: This commit only contains renames. The subsequent commit will
actually make ripgrep build again. We do it this way with the naive hope
that this will make it easier for git history to track the renames.
Sigh.
