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Cache non-symlinks in realpathSync

Rodrigo Muino Tomonari requested to merge github/fork/yallop/cache-non-symlinks into master
Background

The fs.realpathSync function synchronously traverses paths componentwise to resolve symbolic links.

The optional cache argument stores the results of resolution to avoid repeated lookups. The cache can be used to override resolution and to store the results of calls to readlinkSync.

However, the cache only records paths that lstat reveals to be symlinks. Consequently, a call to fs.realpathSync for a path without symlinks may result in many calls to lstat, even if most parts of the path have been resolved in an earlier call.

Checklist
  • make -j4 test (UNIX), or vcbuild test nosign (Windows) passes
  • commit message follows commit guidelines
Affected core subsystem(s)

fs

Description of change

This tiny patch extends fs.realpathSync to record the results for paths that are not symlinks. The code suggests that this was originally the intention, since the cache is expected to contain entries that resolve to themselves:

cache.get(base) === base

With this patch a run of ember build on a fresh application makes around 6,200 fewer lstat calls (out of a total of around 70,000 syscalls). On a typical native file system the performance difference is negligible, but in situations where a syscall has more significant overhead it can be a worthwhile saving. For example, with a file system that forwards operations over a socket via FUSE this patch saves around 10% of the build time.

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