Add process information cache to avoid duplicate lookups

PreMatch and full match phases each created a fresh InboundContext,
causing process search (expensive OS syscalls) to run twice per
connection. Use a freelru ShardedLRU cache with 200ms TTL to serve
the second lookup from cache.

route/router.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"os"
 	"runtime"
+	"time"
 
 	"github.com/sagernet/sing-box/adapter"
 	"github.com/sagernet/sing-box/common/process"
@@ -12,8 +13,11 @@ import (
 	"github.com/sagernet/sing-box/log"
 	"github.com/sagernet/sing-box/option"
 	R "github.com/sagernet/sing-box/route/rule"
+	"github.com/sagernet/sing/common"
 	E "github.com/sagernet/sing/common/exceptions"
 	"github.com/sagernet/sing/common/task"
+	"github.com/sagernet/sing/contrab/freelru"
+	"github.com/sagernet/sing/contrab/maphash"
 	"github.com/sagernet/sing/service"
 	"github.com/sagernet/sing/service/pause"
 )
@@ -34,6 +38,7 @@ type Router struct {
 	ruleSets          []adapter.RuleSet
 	ruleSetMap        map[string]adapter.RuleSet
 	processSearcher   process.Searcher
+	processCache      freelru.Cache[processCacheKey, processCacheEntry]
 	pauseManager      pause.Manager
 	trackers          []adapter.ConnectionTracker
 	platformInterface adapter.PlatformInterface
@@ -141,6 +146,11 @@ func (r *Router) Start(stage adapter.StartStage) error {
 				}
 			}
 		}
+		if r.processSearcher != nil {
+			processCache := common.Must1(freelru.NewSharded[processCacheKey, processCacheEntry](256, maphash.NewHasher[processCacheKey]().Hash32))
+			processCache.SetLifetime(200 * time.Millisecond)
+			r.processCache = processCache
+		}
 	case adapter.StartStatePostStart:
 		for i, rule := range r.rules {
 			monitor.Start("initialize rule[", i, "]")