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Re: Warning regarding global wxStrings and thread-safety


Interesting.  I also found this:

  // NB: In UTF-8 build, (non-const) iterator needs to keep reference
  //     to the underlying wxStringImpl, because UTF-8 is variable-length
  //     encoding and changing the value pointer to by an iterator (using
  //     its operator*) requires calling wxStringImpl::replace() if the old
  //     and new values differ in their encoding's length.
  //     Furthermore, the replace() call may invalid all iterators for the
  //     string, so we have to keep track of outstanding iterators and update
  //     them if replace() happens.
  //     This is implemented by maintaining linked list of iterators for every
  //     string and traversing it in wxUniCharRef::operator=(). Head of the
  //     list is stored in wxString. (FIXME-UTF8)
At least they have a “FIXME” for it. :(


> On 2 Aug 2018, at 18:05, Seth Hillbrand <seth@xxxxxxxxxxxxx> wrote:
> Hi Jeff-
> Good find.  I note here (http://docs.wxwidgets.org/3.0/classwx_string.html <http://docs.wxwidgets.org/3.0/classwx_string.html>) that the use of wxString is explicitly discouraged:
> "While the use of wxString is unavoidable in wxWidgets program, you are encouraged to use the standard string classes std::string or std::wstring in your applications and convert them to and from wxString only when interacting with wxWidgets."
> I imagine that this or similar is what they had in mind.
> -S
> Am Do., 2. Aug. 2018 um 10:02 Uhr schrieb Jeff Young <jeff@xxxxxxxxx <mailto:jeff@xxxxxxxxx>>:
> I finally caught a long-standing but very infrequent crash in the debugger.  It’s somewhat harrowing.
> wxString keeps multiple iterators on a string up-to-date with regard to editing.  It keeps them in a linked list.  If you reference a global string in a thread (even in a const manner, such as taking its length), wxString will create an interator in your thread, link it into the list, and then unlink it when done (with no thread safety).  Sooner or later, this will crash.
> This is the offending line:
>    wxString wildcard = wxT( "*." ) + KiCadFootprintFileExtension;
> Looks innocuous enough, doesn’t it?
> Anyway, something to keep in mind….
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