server: a query that finds every permit taken waits for one instead of failing, the budget is 64, permit and upstream turns wait on a futex with one thread each, the thread pool has no task limit, and transparent huge pages are off for the process

src/server/doh_server.zig

@@ -91,7 +91,6 @@ pub const Snapshot = struct {
     idle_timeouts: u64,
     connection_errors: u64,
     bad_requests: u64,
-    dropped_no_permit: u64,
 };
 
 pub const DohServer = struct {
@@ -117,6 +116,7 @@ pub const DohServer = struct {
         pub const Owner = DohServer;
         pub const ConnPayload = Payload;
         pub const serveConn = serveOne;
+        pub const closing = wakeBudgetWaiters;
         pub const read_buffer_len = recv_buffer_len;
         pub const write_buffer_len = send_buffer_len;
         pub const log = std.log.scoped(.doh_server);
@@ -165,7 +165,6 @@ pub const DohServer = struct {
             .idle_timeouts = core.idle_timeouts.load(.monotonic),
             .connection_errors = core.connection_errors.load(.monotonic),
             .bad_requests = self.stats.bad_requests.load(.monotonic),
-            .dropped_no_permit = core.dropped_no_permit.load(.monotonic),
         };
     }
 
@@ -174,6 +173,10 @@ pub const DohServer = struct {
         self.core.serve(io);
     }
 
+    fn wakeBudgetWaiters(self: *DohServer, io: std.Io) void {
+        self.budget.wakeWaiters(io);
+    }
+
     pub fn deinit(self: *DohServer, io: std.Io) void {
         self.core.deinit(io);
         self.* = undefined;
@@ -389,10 +392,10 @@ pub const DohServer = struct {
         request: *http.Server.Request,
         query: []const u8,
     ) error{ WriteFailed, HttpExpectationFailed }!Next {
-        const work = self.budget.tryAcquire(io) orelse {
-            listener.bump(&self.core.stats.dropped_no_permit);
-            return .close;
-        };
+        // Bounded like a read: a query still waiting when the idle budget runs
+        // out closes the connection, with the timeout counted by the budget.
+        const permit_deadline: std.Io.Clock.Timestamp = .fromNow(io, self.options.idle_timeout);
+        const work = self.budget.acquire(io, permit_deadline, &self.core.run_state) catch return .close;
         defer self.budget.release(io, work);
 
         const outcome = self.handler.handle(