[Xapian-tickets] [Xapian] #665: Avoid C library functions not guaranteed to be thread-safe

[Xapian]

#665: Avoid C library functions not guaranteed to be thread-safe
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 Reporter:  Olly Betts   |             Owner:  Olly Betts
     Type:  defect       |            Status:  assigned
 Priority:  highest      |         Milestone:  1.5.0
Component:  Library API  |           Version:  git master
 Severity:  normal       |        Resolution:
 Keywords:               |        Blocked By:
 Blocking:               |  Operating System:  All
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Comment (by Olly Betts):

 The Linux man pages seem to have been rewritten to be much clearer about
 the nuances of thread safety since we started on this (or maybe I failed
 to fully take in what they were saying before now).

 The key point to grasp is that functions that modify the environment are
 not safe to call in a multi-threaded program, but that means that in a
 multi-threaded program they should not be called so the environment can be
 considered as effectively constant and functions which only read it (like
 `getenv()`) are therefore safe.

 It's not great that in our situation this logic means relying on the code
 of the application using Xapian to not modify the environment if it uses
 threading, but we have to rely on it not to invoke undefined behaviour in
 general.

 I think this means we can probably keep using `getenv()` but that we
 should only use it in the thread that we're called in.  We don't currently
 create separate threads of our own, but if/when we start to we should
 avoid calling `getenv()` in those threads as the application code may be
 single-threaded and thus call `setenv()`.

 It's still useful to eliminate calls to `strtod()` as that suffers from
 changing behaviour if the locale is changed.  I have a WIP branch to do
 that.
-- 
Ticket URL: <https://trac.xapian.org/ticket/665#comment:22>
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