add thread control via wake hints

src/threads.zig

@@ -9,6 +9,7 @@ const AtomicU32 = std.atomic.Atomic(u32);
 const Signals = struct {
     quit: AtomicBool,
     processed: AtomicU32,
+    eof_block: AtomicU32,
 
     const Self = @This();
 
@@ -16,6 +17,7 @@ const Signals = struct {
         return Self{
             .quit = AtomicBool.init(false),
             .processed = AtomicU32.init(0),
+            .eof_block = AtomicU32.init(0),
         };
     }
 };
@@ -69,6 +71,21 @@ pub const ThreadManager = struct {
         self.arena.deinit();
         self.job_pool.deinit();
     }
+
+    pub fn quit(self: *Self) void {
+        self.signals.quit.store(true, .Release);
+        self.unblock();
+        for (self.threads.items) |thread| {
+            thread.join();
+        }
+    }
+
+    pub fn eof(self: *Self) void {
+        self.signals.eof_block.store(1, .Release);
+    }
+    pub fn unblock(self: *Self) void {
+        self.signals.eof_block.store(0, .Release);
+    }
 };
 
 fn quantize_loop(queue: *util.JobQueue, signals: *Signals, Q_Lum: *util.QTable, Q_Chrom: *util.QTable) void {
@@ -76,5 +93,8 @@ fn quantize_loop(queue: *util.JobQueue, signals: *Signals, Q_Lum: *util.QTable,
         const job = queue.pop() orelse continue;
         transform.quantize(job.source, job.target, if (job.is_lum) Q_Lum else Q_Chrom);
         _ = @atomicRmw(u32, &signals.processed.value, .Add, 1, .SeqCst);
+        if (signals.eof_block.load(.Acquire) == 1) {
+            std.Thread.Futex.wait(&signals.eof_block, 1);
+        }
     }
 }