feat(policy): add system load average as checker input

Signed-off-by: Xe Iaso <me@xeiaso.net>

lib/policy/expressions/loadavg.go

@@ -0,0 +1,67 @@
+package expressions
+
+import (
+	"context"
+	"log/slog"
+	"sync"
+	"time"
+
+	"github.com/shirou/gopsutil/v4/load"
+)
+
+type loadAvg struct {
+	lock sync.RWMutex
+	data *load.AvgStat
+}
+
+func (l *loadAvg) updateThread(ctx context.Context) {
+	ticker := time.NewTicker(15 * time.Second)
+	defer ticker.Stop()
+
+	for {
+		select {
+		case <-ticker.C:
+			l.update()
+		case <-ctx.Done():
+			return
+		}
+	}
+}
+
+func (l *loadAvg) update() {
+	l.lock.Lock()
+	defer l.lock.Unlock()
+
+	var err error
+	l.data, err = load.Avg()
+	if err != nil {
+		slog.Debug("can't get load average", "err", err)
+	}
+}
+
+var (
+	globalLoadAvg *loadAvg
+)
+
+func init() {
+	globalLoadAvg = &loadAvg{}
+	go globalLoadAvg.updateThread(context.Background())
+}
+
+func Load1() float64 {
+	globalLoadAvg.lock.RLock()
+	defer globalLoadAvg.lock.RUnlock()
+	return globalLoadAvg.data.Load1
+}
+
+func Load5() float64 {
+	globalLoadAvg.lock.RLock()
+	defer globalLoadAvg.lock.RUnlock()
+	return globalLoadAvg.data.Load5
+}
+
+func Load15() float64 {
+	globalLoadAvg.lock.RLock()
+	defer globalLoadAvg.lock.RUnlock()
+	return globalLoadAvg.data.Load15
+}