From 23d25dbb9e4e469eb2e59d50bd888b7a61ffb876 Mon Sep 17 00:00:00 2001
From: Andrew Kelley <andrew@ziglang.org>
Date: Fri, 9 Jan 2026 19:21:59 -0800
Subject: [PATCH] std.process.Child.collectOutput: change back to other impl

this one avoids calling poll() more than necessary
---
 lib/std/Io.zig            |  2 +-
 lib/std/process/Child.zig | 86 +++++++++++++++++++--------------------
 2 files changed, 43 insertions(+), 45 deletions(-)

diff --git a/lib/std/Io.zig b/lib/std/Io.zig
index d916bb6995..2f34dc07e4 100644
--- a/lib/std/Io.zig
+++ b/lib/std/Io.zig
@@ -260,7 +260,7 @@ pub const Operation = union(enum) {
     file_read_streaming: FileReadStreaming,
 
     pub const Noop = struct {
-        reserved: [2]usize,
+        reserved: [2]usize = .{ 0, 0 },
         status: Status(void) = .{ .result = {} },
     };
 
diff --git a/lib/std/process/Child.zig b/lib/std/process/Child.zig
index 9d31b77080..364c52446f 100644
--- a/lib/std/process/Child.zig
+++ b/lib/std/process/Child.zig
@@ -137,7 +137,6 @@ pub const CollectOutputOptions = struct {
     allocator: ?Allocator = null,
     stdout_limit: Io.Limit = .unlimited,
     stderr_limit: Io.Limit = .unlimited,
-    timeout: Io.Timeout = .none,
 };
 
 /// Collect the output from the process's stdout and stderr. Will return once
@@ -147,55 +146,54 @@ pub const CollectOutputOptions = struct {
 /// The process must have been started with stdout and stderr set to
 /// `process.SpawnOptions.StdIo.pipe`.
 pub fn collectOutput(child: *const Child, io: Io, options: CollectOutputOptions) CollectOutputError!void {
+    const files: [2]Io.File = .{ child.stdout.?, child.stderr.? };
     const lists: [2]*std.ArrayList(u8) = .{ options.stdout, options.stderr };
     const limits: [2]Io.Limit = .{ options.stdout_limit, options.stderr_limit };
-
-    if (options.allocator) |gpa| {
-        for (lists) |list| try list.ensureUnusedCapacity(gpa, 1);
-    } else {
-        for (lists) |list| {
-            if (list.unusedCapacitySlice().len == 0)
-                return error.StreamTooLong;
-        }
-    }
-
+    var dones: [2]bool = .{ false, false };
+    var reads: [2]Io.Operation = undefined;
     var vecs: [2][1][]u8 = undefined;
-    for (lists, &vecs) |list, *vec|
-        vec[0] = list.unusedCapacitySlice();
-
-    var operations: [2]Io.Operation = .{
-        .{ .file_read_streaming = .{
-            .file = child.stdout.?,
-            .data = &vecs[0],
-        } },
-        .{ .file_read_streaming = .{
-            .file = child.stderr.?,
-            .data = &vecs[1],
-        } },
-    };
-
-    var batch: Io.Batch = .init(&operations);
-    batch.submit(io);
-    defer batch.cancel(io);
-
-    var pending = operations.len;
-    var retry_index: ?usize = null;
-    while (pending > 0) {
-        const resubmissions: []const usize = if (retry_index) |i| &.{i} else &.{};
-        const index = try batch.wait(io, resubmissions, options.timeout);
-        const n = try operations[index].file_read_streaming.status.result;
-        if (n == 0) {
-            pending -= 1;
-        } else {
-            retry_index = index;
-            const list = lists[index];
-            const limit = limits[index];
-            list.items.len += n;
-            if (list.items.len >= @intFromEnum(limit)) return error.StreamTooLong;
+    while (true) {
+        for (&reads, &lists, &files, dones, &vecs) |*read, list, file, done, *vec| {
+            if (done) {
+                read.* = .{ .noop = .{} };
+                continue;
+            }
             if (options.allocator) |gpa| try list.ensureUnusedCapacity(gpa, 1);
             const cap = list.unusedCapacitySlice();
             if (cap.len == 0) return error.StreamTooLong;
-            vecs[index][0] = cap;
+            vec[0] = cap;
+            read.* = .{ .file_read_streaming = .{
+                .file = file,
+                .data = vec,
+            } };
         }
+        var all_done = true;
+        var any_canceled = false;
+        var other_err: (error{StreamTooLong} || Io.File.Reader.Error)!void = {};
+        try io.vtable.batch(io.userdata, &reads);
+        for (&reads, &lists, &limits, &dones) |*read, list, limit, *done| {
+            if (done.*) continue;
+            const n = read.file_read_streaming.status.result catch |err| switch (err) {
+                error.Canceled => {
+                    any_canceled = true;
+                    continue;
+                },
+                error.WouldBlock => continue,
+                else => |e| {
+                    other_err = e;
+                    continue;
+                },
+            };
+            if (n == 0) {
+                done.* = true;
+            } else {
+                all_done = false;
+            }
+            list.items.len += n;
+            if (list.items.len > @intFromEnum(limit)) other_err = error.StreamTooLong;
+        }
+        if (any_canceled) return error.Canceled;
+        try other_err;
+        if (all_done) return;
     }
 }