1536109 - NSPRIOInterposer doesn't interpose nsLocalFile.exists

Status: NEW

(Core :: Gecko Profiler, enhancement, P2)

Description

[Florian Quèze [:florian]]

On Windows, calling nsLocalFile.exists will show a 'stat' marker in the profile when profiling with the mainthreadio feature.

On Linux/OSX we don't have markers when calling nsLocalFile.exists. We still have 'stat' markers when the some code queries the size of a file.

This is because NSPRIOInterposer interposes FileInfo and FileInfo64, but not 'access' which is used directly by nsLocalFileUnix.

Comment 1

[:Gijs (he/him)]

Does this explain all the stats that get reported in bug 1579607 and the last few comments of bug 1543752 , or should there be a separate bug for incomplete reports of stat on Linux?

Comment 2

[Florian Quèze [:florian]]

My understanding is that:

• On Windows we intercept the I/O syscalls at the operating system level (PoisonIOInterposer).
• On Unix we instead intercept it within the gecko platform (NSPRIOInterposer), which means that we get I/O markers for main thread I/O done by Gecko code, but not for main thread I/O done by OS functions we are calling (eg. gtk functions). I think this is the reason for not seeing bug 1579607 in profiles.
• The NSPRIOInterposer support for stat calls is incomplete: it will produce markers when some code is checking the file size or last modified date of a file, but won't produce markers when checking if a file exists. This is what this bug is about.