[Bug binutils/30969] New: ar cannot be safely invoked in parallel on windows

[sterpumihai at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30969

            Bug ID: 30969
           Summary: ar cannot be safely invoked in parallel on windows
           Product: binutils
           Version: 2.42 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: sterpumihai at gmail dot com
  Target Milestone: ---

Created attachment 15167
  --> https://sourceware.org/bugzilla/attachment.cgi?id=15167&action=edit
patch for adding getpid() to temp file name

It seems there is a race condition in ar which is closely related to the usage
of mkstemp in function make_tempname (bucomm.c).

In certain situations, due to the implementation of mkstemp, the same "unique"
file name is generated.

This results in a sporadic error of ar:
"ar.exe: could not create temporary file whilst writing archive: Permission
denied"

I repoduced this on Windows on a test system where ar was invoked in parallel.
My investigation revealed that all ar invocations used the same temporary file
name, "stP1kAlM". This is because the implementation of mkstemp provided by
gnulib always uses seed value 0. They do use clock() but given ar calls mkstemp
pretty quick, the resolution of clock() on Windows (millisecond) yields the
same result.

There are basically two solutions here:
1. Investigate and fix the race condition (might prove difficult) OR
2. Add some process specific information to the temporary file name.

I personally used getpid() and appended it between "st" and "XXXXXX" so each ar
invocation truly has a different temporary file. See attached patch.

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