From ae1a102882103221ef842176dfd8cb1090d5f591 Mon Sep 17 00:00:00 2001
From: Ophestra Umiker <cat@ophivana.moe>
Date: Sat, 26 Oct 2024 23:09:32 +0900
Subject: fmsg: support temporarily withholding output

Trying to print to a shared stdout is a terrible idea. This change makes it possible to withhold output for the lifetime of the sandbox.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>
---
 internal/fmsg/defer.go | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)
 create mode 100644 internal/fmsg/defer.go

(limited to 'internal/fmsg/defer.go')

diff --git a/internal/fmsg/defer.go b/internal/fmsg/defer.go
new file mode 100644
index 00000000..cee3c737
--- /dev/null
+++ b/internal/fmsg/defer.go
@@ -0,0 +1,70 @@
+package fmsg
+
+import (
+	"os"
+	"sync"
+	"sync/atomic"
+)
+
+var (
+	wstate   atomic.Bool
+	withhold = make(chan struct{}, 1)
+	msgbuf   = make(chan dOp, 64) // these ops are tiny so a large buffer is allocated for withholding output
+
+	dequeueOnce sync.Once
+	queueSync   sync.WaitGroup
+)
+
+func dequeue() {
+	go func() {
+		for {
+			select {
+			case op := <-msgbuf:
+				op.Do()
+				queueSync.Done()
+			case <-withhold:
+				<-withhold
+			}
+		}
+	}()
+}
+
+type dOp interface{ Do() }
+
+func Exit(code int) {
+	queueSync.Wait()
+	os.Exit(code)
+}
+
+func Withhold() {
+	if wstate.CompareAndSwap(false, true) {
+		withhold <- struct{}{}
+	}
+}
+
+func Resume() {
+	if wstate.CompareAndSwap(true, false) {
+		withhold <- struct{}{}
+	}
+}
+
+type dPrint []any
+
+func (v dPrint) Do() {
+	std.Print(v...)
+}
+
+type dPrintf struct {
+	format string
+	v      []any
+}
+
+func (d *dPrintf) Do() {
+	std.Printf(d.format, d.v...)
+}
+
+type dPrintln []any
+
+func (v dPrintln) Do() {
+	std.Println(v...)
+}
-- 
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