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, 13 insertions, 0 deletions

diff --git a/cli/tests/testdata/run/stdout_write_all.ts b/cli/tests/testdata/run/stdout_write_all.ts
new file mode 100644
index 000000000..cfb2981e4
--- /dev/null
+++ b/cli/tests/testdata/run/stdout_write_all.ts
@@ -0,0 +1,13 @@
+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 < 100; i++) {
+  pending.push(Deno.stdout.write(encoder.encode("Hello, ")));
+  pending.push(Deno.stdout.write(encoder.encode(`world! ${i}`)));
+  pending.push(Deno.stdout.write(encoder.encode("\n")));
+}
+
+await Promise.all(pending);