add sysutil

sysutil/sysutil.go

@@ -0,0 +1,23 @@
+package sysutil
+
+import (
+	"runtime/debug"
+)
+
+// SetMaxThreads sets the maximum number of operating system
+// threads that the Go program can use. If it attempts to use more than
+// this many, the program crashes.
+// SetMaxThreads returns the previous setting.
+// The initial setting is 10,000 threads.
+//
+// The limit controls the number of operating system threads, not the number
+// of goroutines. A Go program creates a new thread only when a goroutine
+// is ready to run but all the existing threads are blocked in system calls, cgo calls,
+// or are locked to other goroutines due to use of runtime.LockOSThread.
+//
+// SetMaxThreads is useful mainly for limiting the damage done by
+// programs that create an unbounded number of threads. The idea is
+// to take down the program before it takes down the operating system.
+func SetMaxThreads(threads int) int {
+	return debug.SetMaxThreads(threads)
+}

sysutil/sysutil_test.go

@@ -0,0 +1,20 @@
+package sysutil
+
+import (
+	"runtime/debug"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSetMaxThreads(t *testing.T) {
+	originalMaxThreads := debug.SetMaxThreads(10000)
+	defer debug.SetMaxThreads(originalMaxThreads)
+
+	newMaxThreads := 5000
+	previousMaxThreads := SetMaxThreads(newMaxThreads)
+	require.Equal(t, 10000, previousMaxThreads, "Expected previous max threads to be 10000")
+	require.Equal(t, newMaxThreads, debug.SetMaxThreads(newMaxThreads), "Expected max threads to be set to 5000")
+
+	SetMaxThreads(originalMaxThreads)
+}