Hold a read that has nothing yet and answer it when its file has news

A following log, event, pty/data or a pty/run before its answer used to
answer .again and wait for a wakeAll, which only the parked-write path
asked for, so the band-aid had every queue push set turn.parked. Now the
core keeps such a read (ctlfs.hold) and, as the turn is given up after
anything that queued a record, ran a command out or closed a pane,
answers it on its own connection, the way factotum answers the log reads
it keeps and acme an event read. Only a read the engine still holds
parked is answered, because cloud9 tells the backend nothing of a
Tflush, so a flushed read spends no record.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 5 insertions, 5 deletions

diff --git a/src/ninep/events.zig b/src/ninep/events.zig
index bd5fecf3..6b8c744e 100644
--- a/src/ninep/events.zig
+++ b/src/ninep/events.zig
@@ -50,10 +50,6 @@ pub const Queue = struct {
             q.buf.shrinkRetainingCapacity(q.buf.items.len - 4);
             return;
         };
-        // A read parked on this queue is retried only when the turn is next
-        // given up with `parked` set; without it a follower sleeps until some
-        // unrelated request happens to park.
-        pardes.turn.parked = true;
     }
 
     pub fn peek(q: *const Queue) ?[]const u8 {
@@ -105,7 +101,7 @@ pub fn pending(q: *const Queue) u64 {
     return record.len;
 }
 
-/// One record per read; `.again` parks the read until a record arrives.
+/// One record per read; `.again` holds the read until a record arrives.
 pub fn readQueue(p: *Pardes, req: Req, q: *Queue) Reply {
     const record = q.peek() orelse return .{ .tag = req.tag, .status = .again };
     if (req.size < record.len) return Reply.fail(req.tag, E.INVAL);
@@ -129,6 +125,7 @@ pub fn noteInstall(p: *Pardes, id: usize) void {
 pub fn noteRetire(p: *Pardes, id: usize, pane: *Pane) void {
     if (id >= MAX_PANES) return;
     tree.pty.shellGone(p, id);
+    p.fs.news = true; // a read held on its event or pty/data hears it went
     if (p.fs.panes[id].unannounced) {
         p.fs.panes[id].unannounced = false;
         return;
@@ -174,6 +171,7 @@ fn pushLog(p: *Pardes, record: []u8) void {
     while (end > 0 and record[end] & 0xC0 == 0x80) end -= 1;
     record[end] = '\n';
     p.fs.log.push(p.gpa, record[0 .. end + 1]);
+    p.fs.news = true;
 }
 
 /// An open freezes the ring's text, so `cat log` answers what happened lately
@@ -384,6 +382,7 @@ pub fn noteAction(
     var buf: [max_record_text + 64]u8 = undefined;
     const record = formatRecord(&buf, p.fs.origin, action, q0, q1, flag, text);
     p.fs.panes[id].events.push(p.gpa, record);
+    p.fs.news = true;
     return true;
 }
 
@@ -397,6 +396,7 @@ pub fn notePtyOutput(p: *Pardes, id: usize, bytes: []const u8) void {
         pf.pty_out.push(p.gpa, bytes[off..][0..n]);
         off += n;
     }
+    p.fs.news = true;
 }
 
 const EventRecord = struct { action: Action, q0: u32, q1: u32 };