Rewritten without async

main.py

@@ -1,36 +1,107 @@
-import asyncio
-import contextlib
+from functools import partial
 import random
 
 
+class Cell(object):
+    def __init__(self):
+        self.is_set = False
+        self.value = None
+
+    def set(self, x):
+        self.is_set = True
+        self.value = x
+
+
+class Merge(object):
+    def __init__(self, xs, ys, on_complete):
+        self.xs = xs[:]
+        self.ys = ys[:]
+        self.output = []
+        self.on_complete = on_complete
+        self.running = True
+
+        self.settle()
+
+    def touch(self):
+        # print(f"Touching: {self}")
+        if ask(self.xs[0], self.ys[0]):
+            self.output.append(self.xs.pop(0))
+        else:
+            self.output.append(self.ys.pop(0))
+
+        self.settle()
+
+    def settle(self):
+        if len(self.xs) == 0:
+            self.output += self.ys
+            self.ys = []
+            self.complete()
+            return
+
+        if len(self.ys) == 0:
+            self.output += self.xs
+            self.xs = []
+            self.complete()
+            return
+
+    def complete(self):
+        self.on_complete(self.output)
+        self.running = False
+
+    def __repr__(self):
+        return f"Merge({self.xs}, {self.ys}, {self.output})"
+
+
+def _sort(xs, merges, on_complete):
+    if len(xs) < 2:
+        on_complete(xs[:])
+        return
+
+    half = len(xs) // 2
+    fst = xs[:half]
+    snd = xs[half:]
+    sorted_fst = Cell()
+    sorted_snd = Cell()
+
+    def cb(setter, value):
+        setter(value)
+        if sorted_fst.is_set and sorted_snd.is_set:
+            new_merge = Merge(sorted_fst.value, sorted_snd.value, on_complete)
+            merges.append(new_merge)
+
+    _sort(fst, merges, partial(cb, sorted_fst.set))
+    _sort(snd, merges, partial(cb, sorted_snd.set))
+
+
+def merge_sort(xs):
+    merges = []
+    result = Cell()
+    _sort(xs, merges, result.set)
+
+    while True:
+        # replace in place
+        for i in reversed(range(len(merges))):
+            if not merges[i].running:
+                merges.pop(i)
+
+        if len(merges) == 0:
+            break
+
+        # print(f"Number of ongoing merges: {merges}")
+        # print(f"Number of ongoing merges: {len(merges)}")
+        random.shuffle(merges)
+        for m in merges[:]:
+            m.touch()
+
+    assert result.is_set
+    return result.value
+
+
 TRUTHY = "y yes 1 t true aye left up top first p".split()
 FALSEY = "n no 0 2 f false nay right down bottom second nil".split()
 
 
-def sort(options):
-    loop = asyncio.new_event_loop()
-    postponed_questions = []
-
-    # counter for how many threads can still resume
-    # if it's 0, then we need to ask some questions or else we're deadlocked
-
-    n_active = 0
-
-    @contextlib.asynccontextmanager
-    async def semaphore(amt):
-        nonlocal n_active
-        n_active += amt
-        yield
-        n_active -= amt
-
-    def deadlocked():
-        return n_active == 0
-
-    async def ask(x, y):
-        async with semaphore(-1):
-            future = loop.create_future()
-
-            def ask_question():
+def ask(x, y):
     if random.choice([False, True]):
         yes_result = True
         a, b = x, y
@@ -41,72 +112,23 @@ def sort(options):
     while True:
         choice = input(f"Is {a} better than {b}? ")
         if choice in TRUTHY:
-                        future.set_result(yes_result)
-                        return
+            return yes_result
 
         if choice in FALSEY:
-                        future.set_result(not yes_result)
-                        return
+            return not yes_result
 
         print(f"Huh? I didn't understand {choice}. Answer \"y\" or \"n\".")
 
-            postponed_questions.append(ask_question)
-            if deadlocked():
-                await ask_questions()
-
-            return await future
-
-    async def merge(xs, ys):
-        async with semaphore(1):
-            xs = xs[:]
-            ys = ys[:]
-            out = []
-
-            while len(xs) > 0 and len(ys) > 0:
-                if await ask(xs[0], ys[0]):
-                    out.append(xs.pop(0))
-                else:
-                    out.append(ys.pop(0))
-
-            out.extend(xs)
-            out.extend(ys)
-            return out
-
-    async def merge_sort(xs):
-        if len(xs) < 2:
-            return xs[:]
-
-        half = len(xs) // 2
-
-        fst_half, snd_half = await asyncio.gather(
-            merge_sort(xs[:half]),
-            merge_sort(xs[half:])
-        )
-
-        return await merge(fst_half, snd_half)
-
-    async def ask_questions():
-        ppq = postponed_questions[:]
-        postponed_questions.clear()
-
-        random.shuffle(ppq)
-        for q in ppq:
-            q()
-
-    result_future = merge_sort(options)
-    result = loop.run_until_complete(result_future)
-    return result
-
 
 def main():
     with open("input.txt", "rt") as f_in:
         lines_in = [i.strip() for i in f_in.read().split("\n") if i.strip()]
 
     random.shuffle(lines_in)
-    results = sort(lines_in)
+    results = merge_sort(lines_in)
 
     with open("output.txt", "wt") as f_out:
-        f_out.writelines(results)
+        f_out.write("\n".join(results))
 
 
 if __name__ == '__main__':