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Ignore return of SymInitializeW on Windows #231

Merged
merged 1 commit into from
Jul 31, 2019
Merged

Ignore return of SymInitializeW on Windows #231

merged 1 commit into from
Jul 31, 2019

Commits on Jul 31, 2019

  1. Ignore return of SymInitializeW on Windows 

    This commit updates the behavior of backtraces on Windows to execute
`SymInitializeW` globally once-per-process and ignore the return value
as to whether it succeeded or not. This undoes previous work in this
crate to specifically check the return value, and this is a behavior
update for the standard library when this goes into the standard
library.

The `SymInitializeW` function is required to be called on MSVC before
any backtraces can be captured or before any addresses can be
symbolized. This function is quite slow. It can only be called
once-per-process and there's a corresponding `SymCleanup` to undo the
work of `SymInitializeW`.

The behavior of what to do with `SymInitializeW` has changed a lot over
time in this crate. The very first implementation for Windows paired
with `SymCleanup`. Then reports of slowness at rust-lang/rustup#591
led to ac8c6d2 where `SymCleanup` was removed. This led to #165 where
because the standard library still checked `SymInitializeW`'s return
value and called `SymCleanup` generating a backtrace with this crate
would break `RUST_BACKTRACE=1`. Finally (and expectedly) the performance
report has come back as #229 for this crate.

I'm proposing that the final nail is put in this coffin at this point
where this crate will ignore the return value of `SymInitializeW`,
initializing symbols once per process globally. This update will go into
the standard library and get updated on the stable channel eventually,
meaning both libstd and this crate will be able to work with one another
and only initialize the process's symbols once globally. This does mean
that there will be a period of "breakage" where we will continue to make
`RUST_BACKTRACE=1` not useful if this crate is used on MSVC, but that's
sort of the extension of the status quo as of a month or so ago. This
will eventually be fixed once the stable channel of Rust is updated.
    @alexcrichton
    alexcrichton committed Jul 31, 2019
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