fix(cli): synchronize async stdio/file reads and writes (#15092)

Fixes a regression where async writes and reads could get out of order.

1 files changed, 17 insertions, 0 deletions

diff --git a/cli/tests/testdata/run/stdin_read_all.ts b/cli/tests/testdata/run/stdin_read_all.ts
new file mode 100644
index 000000000..d683a2bf6
--- /dev/null
+++ b/cli/tests/testdata/run/stdin_read_all.ts
@@ -0,0 +1,17 @@
+const encoder = new TextEncoder();
+
+const pending = [];
+
+// do this a bunch of times to ensure it doesn't race
+// and everything happens in order
+for (let i = 0; i < 50; i++) {
+  const buf = new Uint8Array(1);
+  pending.push(
+    Deno.stdin.read(buf).then(() => {
+      return Deno.stdout.write(buf);
+    }),
+  );
+}
+
+await Promise.all(pending);
+await Deno.stdout.write(encoder.encode("\n"));