fix O(n^2) perf bug for std::io::fs::walk_dir #13720
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We don't currently have a pressing reason to define a particular ordering of yielded directories from this function, so I'm ok leaving is unspecified. If we want to be conservative, perhaps the documentation could indicate that the order of traversal is subject to change? (not specified) |
The `walk_dir` iterator was simulating a queue using a vector (in particular, using `shift`), leading to O(n^2) performance. Since the order was not well-specified (see issue rust-lang#13411), the simplest fix is to use the vector as a stack (and thus yield a depth-first traversal). This patch does exactly that. It leaves the order as originally specified -- "some top-down order" -- and adds a test to ensure a top-down traversal. Note that the underlying `readdir` function does not specify any particular order, nor does the system call it uses. Closes rust-lang#13411.
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@alexcrichton Updated the patch to revert the spec comment, and changed the test to only ensure some top-down order, rather than depth-first. r? |
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The `walk_dir` iterator was simulating a queue using a vector (in particular, using `shift`), leading to O(n^2) performance. Since the order was not well-specified (see issue #13411), the simplest fix is to use the vector as a stack (and thus yield a depth-first traversal). This patch does exactly that, and adds a test checking for depth-first behavior. Note that the underlying `readdir` function does not specify any particular order, nor does the system call it uses. Closes #13411.
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The
walk_diriterator was simulating a queue using a vector (in particular, usingshift),leading to O(n^2) performance. Since the order was not well-specified (see issue #13411),
the simplest fix is to use the vector as a stack (and thus yield a depth-first traversal).
This patch does exactly that, and adds a test checking for depth-first behavior.
Note that the underlying
readdirfunction does not specify any particular order, nordoes the system call it uses.
Closes #13411.