From be5f559939fc11cbfba95b4a7d518816bec8677a Mon Sep 17 00:00:00 2001
From: Gabriel Schneider <gbrls@0x4200.cafe>
Date: Tue, 29 Sep 2026 13:26:07 -0300
Subject: The GUI's idle wakeup copies no 20 KB message batch

Queue.take built its batch (queue capacity plus room, some 20 KB) and returned it by value on every wakeup, a memset and a memcpy of it though the queue was empty; it led the idle profile. drainQueue now fills a batch the Shell keeps, and an empty queue leaves it untouched.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 src/gui/gui.zig | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

(limited to 'src/gui')

diff --git a/src/gui/gui.zig b/src/gui/gui.zig
index d935b5fd..e110b3ab 100644
--- a/src/gui/gui.zig
+++ b/src/gui/gui.zig
@@ -1061,9 +1061,19 @@ const Queue = struct {
     }
 
     fn take(q: *Queue) MessageBatch {
+        var batch: MessageBatch = .{};
+        q.takeInto(&batch);
+        return batch;
+    }
+
+    /// `take` into a batch the caller keeps: an idle wakeup copies nothing
+    /// (the batch is some 20 KB, and was built and returned by value each
+    /// time).
+    fn takeInto(q: *Queue, batch: *MessageBatch) void {
+        batch.len = 0;
         q.lock();
         defer q.unlock();
-        var batch: MessageBatch = .{};
+        if (q.len == 0 and !q.files_changed and q.completion_len == 0) return;
         while (q.len > 0) {
             batch.items[batch.len] = q.items[q.head];
             batch.len += 1;
@@ -1080,7 +1090,6 @@ const Queue = struct {
         batch.len += q.completion_len;
         q.completion_len = 0;
         std.debug.assert(libc.pthread_cond_broadcast(&q.space) == .SUCCESS);
-        return batch;
     }
 
     fn discardCompletions(q: *Queue) void {
@@ -3999,6 +4008,8 @@ const Shell = struct {
     ptys: *[pardes.MAX_PANES]?Pty,
     gens: *[pardes.MAX_PANES]u32,
     queue: *Queue,
+    /// What drainQueue takes each wakeup, kept rather than rebuilt.
+    batch: MessageBatch = .{},
     pipe_tasks: *PipeTasks,
     inotify_fd: c_int,
     watches: *file_watch.Table,
@@ -4153,7 +4164,8 @@ const Shell = struct {
         s.reconcilePtys();
         // After this batch's output, which an exit is told behind.
         defer s.takeExits();
-        var msgs = s.queue.take();
+        s.queue.takeInto(&s.batch);
+        const msgs = &s.batch;
         var check_files = false;
         for (msgs.slice()) |m| switch (m) {
             .output => |o| {
-- 
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