working solution

submissions/awcheung1213.py

@@ -0,0 +1,73 @@
+"""Parallel build scheduler using Python 3.14t (no GIL).
+
+How it works:
+  1. Find all targets with no dependencies. These will be the entrypoint of the build.
+  2. Queue up all targets with no dependencies.
+  3. When a target finishes, store its build result in a shared state and check its dependents. \
+     If a dependent has all its deps now built, it becomes ready too.
+  4. Repeat until everything is built.
+"""
+
+import os
+import queue
+import threading
+
+from graph import BuildGraph
+
+
+def build_all(graph: BuildGraph) -> dict[str, bytes]:
+    targets = graph.targets
+    number_of_targets = len(targets)
+    if number_of_targets == 0:
+        return {}
+
+    target_to_dependents: dict[str, list[str]] = {name: [] for name in targets}
+    target_to_number_of_dependencies: dict[str, int] = {}
+
+    for name, target in targets.items():
+        target_to_number_of_dependencies[name] = len(target.deps)
+        for dep in target.deps:
+            target_to_dependents[dep.name].append(name)
+
+    task_queue: queue.Queue[str | None] = queue.Queue()
+
+    for name, count in target_to_number_of_dependencies.items():
+        if count == 0:
+            task_queue.put(name)
+
+    builds: dict[str, bytes] = {}
+    lock = threading.Lock()
+    number_of_targets_built = [0]
+    number_of_workers = os.cpu_count() or 24
+
+    def worker():
+        while True:
+            target_name = task_queue.get()
+            if target_name == "ALL_TARGETS_BUILT":
+                return
+
+            target = targets[target_name]
+            dependency_builds = {dependency.name: builds[dependency.name] for dependency in target.deps}
+            result = target.build(dependency_builds)
+
+            with lock:
+                builds[target_name] = result
+                number_of_targets_built[0] += 1
+
+                for dependency_name in target_to_dependents[target_name]:
+                    target_to_number_of_dependencies[dependency_name] -= 1
+                    if target_to_number_of_dependencies[dependency_name] == 0:
+                        task_queue.put(dependency_name)
+
+                if number_of_targets_built[0] == number_of_targets:
+                    for _ in range(number_of_workers):
+                        task_queue.put("ALL_TARGETS_BUILT")
+
+    threads = [threading.Thread(target=worker, daemon=True) for _ in range(number_of_workers)]
+
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+
+    return builds