4 ms·

I see they made the same mistake as POSIX threads in implementing recursive mutexes. Disheartening.

• sparky 15y ago
  Of all the ways to shoot yourself in the foot with C, recursive mutexes seem relatively benign. The implementation is a handful of lines of code, and they're not always a symptom of bad design, either; imagine needing to lock each node in a path through a (possibly cyclic) graph.
  • barrkel 15y ago
    If two different threads were trying to lock different paths that entered the same cycle at different nodes, there can be a deadlock. X -> B B -> C C -> B Y -> C Thread 1 tries to lock X B C; thread 2 tries to lock Y C B; deadlock with 1 holding X and B, 2 holding Y and C. It's possible that your paths may be more restricted than this, but I reckon keeping the paths and cycles clean would be a bigger problem than recursive mutexes.
• shin_lao 15y ago
  Recursive mutexes are useful when you need to implement multithreading a posteriori and cannot evaluate all the locking paths.
  • feb 15y ago
    When adding locking without evaluating all locking paths, how can you be sure none of those paths cause a deadlock ?
    • shin_lao 15y ago
      You cannot self deadlock with a a single recursive mutex.