LibCore: Introduce SharedSingleProducerCircularQueue

This new class with an admittedly long OOP-y name provides a circular
queue in shared memory. The queue is a lock-free synchronous queue
implemented with atomics, and its implementation is significantly
simplified by only accounting for one producer (and multiple consumers).
It is intended to be used as a producer-consumer communication
datastructure across processes. The original motivation behind this
class is efficient short-period transfer of audio data in userspace.

This class includes formal proofs of several correctness properties of
the main queue operations `enqueue` and `dequeue`. These proofs are not
100% complete in their existing form as the invariants they depend on
are "handwaved". This seems fine to me right now, as any proof is better
than no proof :^). Anyways, the proofs should build confidence that the
implemented algorithms, which are only roughly based on existing work,
operate correctly in even the worst-case concurrency scenarios.

1 files changed, 4 insertions, 0 deletions

diff --git a/AK/Debug.h.in b/AK/Debug.h.in
index a4693ffa6c..2861c2e210 100644
--- a/AK/Debug.h.in
+++ b/AK/Debug.h.in
@@ -386,6 +386,10 @@
 #cmakedefine01 SH_LANGUAGE_SERVER_DEBUG
 #endif
 
+#ifndef SHARED_QUEUE_DEBUG
+#cmakedefine01 SHARED_QUEUE_DEBUG
+#endif
+
 #ifndef SHELL_JOB_DEBUG
 #cmakedefine01 SHELL_JOB_DEBUG
 #endif