Build docs with a pre-configured docker

.gitea/workflows/docs.yaml

@@ -22,9 +22,6 @@ jobs:
         with:
           fetch-depth: 0   # full history needed for mkdocs gh-deploy
 
-      - name: Install MkDocs dependencies
-        run: pip install --quiet -r docs/requirements.txt
-
       - name: Configure git identity
         run: |
           git config user.name  "Gitea Actions"

Dockerfile.builder

@@ -16,4 +16,12 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     nodejs \
     && rm -rf /var/lib/apt/lists/*
 
+# Pre-install MkDocs dependencies so the docs workflow does not need to pip
+# install at runtime. --break-system-packages is required because the Debian
+# base marks the environment as externally managed (PEP 668); this is safe in
+# a dedicated container image.
+COPY docs/requirements.txt /tmp/docs-requirements.txt
+RUN pip install --no-cache-dir --break-system-packages -r /tmp/docs-requirements.txt \
+    && rm /tmp/docs-requirements.txt
+
 WORKDIR /src

include/kpn/scheduler.hpp

@@ -69,6 +69,9 @@ public:
             while (!q->pq.empty()) q->pq.pop();
             total_.fetch_sub(discarded, std::memory_order_relaxed);
         }
+        // Lock cv_mx_ before notifying so the stop signal can't be lost in the
+        // gap between a worker's predicate check and its wait() (see submit()).
+        { std::lock_guard<std::mutex> lk(cv_mx_); }
         cv_.notify_all();
         for (auto& t : workers_) if (t.joinable()) t.join();
         workers_.clear();
@@ -91,6 +94,12 @@ public:
         }
         total_.fetch_add(1, std::memory_order_relaxed);
         submitted_.fetch_add(1, std::memory_order_relaxed);
+        // Synchronize with worker_loop's predicate evaluation: taking cv_mx_
+        // here guarantees a worker is either before its predicate check (and
+        // will observe total_ > 0) or already blocked in wait() (and will be
+        // woken). Without this, notify_one() can slip into the gap between the
+        // worker's predicate check and its wait(), and be lost — a deadlock.
+        { std::lock_guard<std::mutex> lk(cv_mx_); }
         cv_.notify_one();
     }
 
@@ -157,8 +166,12 @@ private:
         active_.fetch_sub(1, std::memory_order_relaxed);
         // Notify drain() if this was the last in-flight task.
         // acq_rel ensures the decrement is visible before any drain() load.
-        if (total_.fetch_sub(1, std::memory_order_acq_rel) == 1)
+        // Lock drain_mx_ before notifying to avoid a lost wakeup against
+        // drain()'s predicate check (same hazard as submit()/cv_mx_).
+        if (total_.fetch_sub(1, std::memory_order_acq_rel) == 1) {
+            { std::lock_guard<std::mutex> lk(drain_mx_); }
             drain_cv_.notify_all();
+        }
     }
 
     void worker_loop(std::size_t id) {