SolarMutex: please educate me

[Stephan Bergmann]

On 05/13/2013 07:12 PM, Lionel Elie Mamane wrote:
> Base or Base-related code seems to have some issues around the
> "SolarMutex".
>
> https://bugs.freedesktop.org/show_bug.cgi?id=61725
> https://bugs.freedesktop.org/show_bug.cgi?id=64241
> (and others historically)
>
> Please educate me on the SolarMutex. What is its meaning, when should
> be held/acquired, ... From
> http://cgit.freedesktop.org/libreoffice/core/commit/?id=b34b8d3372364b3c5043da0357ec69505e8d8602,
> my "guess" is that it is related to GUI stuff. Maybe it should be held
> when calling a GUI (that is, GTK/Win32/QT/...) function? But it can't
> be that simple, else vcl would "just do it"... It seems to expect
> higher-level code to hold it already. Why?

Historically, the SolarMutex was assumed to be a clever solution to the 
problem of turning StarOffice from a single-threaded application to a 
multi-threaded one---lock the SolarMutex around any code that is not yet 
thread-safe, and be done with it.  Or so people thought.

The world has long since found out that "single global mutex" is a 
horrible idea for GUI applications (where all GUI frameworks have 
settled on "confine relevant code to run in a single event-loop thread" 
instead).

This leaves us with completely unmaintainable ("where do I need to lock 
SolarMutex?"---"nobody knows for sure") and broken (cf. 
SolarMutexReleaser) code.

Incidentally, I had exactly the same problem with 
<https://gerrit.libreoffice.org/#/c/3894/> "TODO: Ensure SolarMutex is 
locked at DBG_TESTSOLARMUTEX checkpoints" last night.

Stephan