Claude's docstrings

src/ThreadPipeline.h

@@ -9,7 +9,48 @@
 #include <utility>
 #include <vector>
 
+// Multi-stage lock-free pipeline for high-throughput inter-thread
+// communication.
+//
+// Overview:
+// - Items flow through multiple processing stages (stage 0 -> stage 1 -> ... ->
+// final stage)
+// - Each stage can have multiple worker threads processing items in parallel
+// - Uses a shared ring buffer with atomic counters for lock-free coordination
+// - Supports batch processing for efficiency
+//
+// Usage Pattern:
+//   // Producer threads (add items to stage 0):
+//   auto guard = pipeline.push(batchSize, /*block=*/true);
+//   for (auto& item : guard.batch) {
+//     // Initialize item data
+//   }
+//   // Guard destructor publishes batch to consumers
+//
+//   // Consumer threads (process items from any stage):
+//   auto guard = pipeline.acquire(stageNum, threadId, maxBatch,
+//   /*mayBlock=*/true); for (auto& item : guard.batch) {
+//     // Process item
+//   }
+//   // Guard destructor marks items as consumed and available to next stage
+//
+// Memory Model:
+// - Ring buffer size must be power of 2 for efficient masking
+// - Uses 64-bit indices to avoid ABA problems (indices never repeat until
+// uint32_t overflow)
+// - Actual ring slots accessed via: index & (slotCount - 1)
+// - 128-byte aligned atomics prevent false sharing between CPU cache lines
+//
+// Thread Safety:
+// - Fully lock-free using atomic operations with acquire/release memory
+// ordering
+// - Uses C++20 atomic wait/notify for efficient blocking when no work available
+// - RAII guards ensure proper cleanup even with exceptions
 template <class T> struct ThreadPipeline {
+  // Constructor
+  // lgSlotCount: log2 of ring buffer size (e.g., 10 -> 1024 slots)
+  // threadsPerStage: number of threads for each stage (e.g., {1, 4, 2} = 1
+  // producer, 4 stage-1 workers, 2 stage-2 workers)
   ThreadPipeline(int lgSlotCount, const std::vector<int> &threadsPerStage)
       : slotCount(1 << lgSlotCount), slotCountMask(slotCount - 1),
         threadState(threadsPerStage.size()), ring(slotCount) {
@@ -218,6 +259,12 @@ public:
     uint32_t newSlot;
   };
 
+  // Acquire a batch of items for processing by a consumer thread.
+  // stage: which processing stage (0 = first consumer stage after producers)
+  // thread: thread ID within the stage (0 to threadsPerStage[stage]-1)
+  // maxBatch: maximum items to acquire (0 = no limit)
+  // mayBlock: whether to block waiting for items (false = return empty batch if
+  // none available) Returns: StageGuard with batch of items to process
   [[nodiscard]] StageGuard acquire(int stage, int thread, int maxBatch = 0,
                                    bool mayBlock = true) {
     assert(stage < threadState.size());
@@ -226,10 +273,17 @@ public:
     return StageGuard{std::move(batch), &threadState[stage][thread]};
   }
 
-  // Grants exclusive access to a producer thread to a span of up to `size`. If
-  // `block` is true, then this call will block if the queue is full, until the
-  // queue is not full. Otherwise it will return an empty batch if the queue is
-  // full.
+  // Reserve slots in the ring buffer for a producer thread to fill with items.
+  // This is used by producer threads to add new items to stage 0 of the
+  // pipeline.
+  //
+  // size: number of slots to reserve (must be > 0 and <= ring buffer capacity)
+  // block: if true, blocks when ring buffer is full; if false, returns empty
+  // guard Returns: ProducerGuard with exclusive access to reserved slots
+  //
+  // Usage: Fill items in the returned batch, then let guard destructor publish
+  // them. The guard destructor ensures items are published in the correct
+  // order.
   //
   // Preconditions:
   //   - size > 0 (must request at least one slot)