D5966: Fix race-condition in KRandom-seeding.

[Thomas Friedrichsmeier]

tfry created this revision.
Restricted Application added a project: Frameworks.
Restricted Application added a subscriber: Frameworks.

REVISION SUMMARY
  Consider the following scenario: Thread A calls KRandom::random(), for the first time.
  It will now go through a (relatively) expensive procedure to seed the RNG. Note that before
  this patch, "init" is set to true long _before_ the actual call to qsrand().
  Now, thread B calls KRandom::random() in this sensitive time window. Since it finds "init"
  to be true, it will skip over the expensive initialization, and be very likely to arrive at
  qrand(), before thread A had a chance to call qsrand().
  
  This patch is the simplest possible solution: Making sure init is set, _after_ the seed was
  really initialized. This does not prevent init races, but the worst case scenario is now, that
  several threads are each going through the seeding. A more elaborate solution would be to
  add mutex-protection during initialization.

REPOSITORY
  R244 KCoreAddons

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D5966

AFFECTED FILES
  src/lib/randomness/krandom.cpp

To: tfry, dfaure
Cc: tfry, rjvbb, #frameworks
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