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/process_cache.go

@@ -0,0 +1,34 @@
+package route
+
+import (
+	"context"
+	"net/netip"
+
+	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing-box/common/process"
+)
+
+type processCacheKey struct {
+	Network     string
+	Source      netip.AddrPort
+	Destination netip.AddrPort
+}
+
+type processCacheEntry struct {
+	result *adapter.ConnectionOwner
+	err    error
+}
+
+func (r *Router) findProcessInfoCached(ctx context.Context, network string, source netip.AddrPort, destination netip.AddrPort) (*adapter.ConnectionOwner, error) {
+	key := processCacheKey{
+		Network:     network,
+		Source:      source,
+		Destination: destination,
+	}
+	if entry, ok := r.processCache.Get(key); ok {
+		return entry.result, entry.err
+	}
+	result, err := process.FindProcessInfo(r.processSearcher, ctx, network, source, destination)
+	r.processCache.Add(key, processCacheEntry{result: result, err: err})
+	return result, err
+}

route/route.go

@@ -9,7 +9,6 @@ import (
 	"time"
 
 	"github.com/sagernet/sing-box/adapter"
-	"github.com/sagernet/sing-box/common/process"
 	"github.com/sagernet/sing-box/common/sniff"
 	C "github.com/sagernet/sing-box/constant"
 	R "github.com/sagernet/sing-box/route/rule"
@@ -415,7 +414,7 @@ func (r *Router) matchRule(
 		} else if metadata.Destination.IsIP() {
 			originDestination = metadata.Destination.AddrPort()
 		}
-		processInfo, fErr := process.FindProcessInfo(r.processSearcher, ctx, metadata.Network, metadata.Source.AddrPort(), originDestination)
+		processInfo, fErr := r.findProcessInfoCached(ctx, metadata.Network, metadata.Source.AddrPort(), originDestination)
 		if fErr != nil {
 			r.logger.InfoContext(ctx, "failed to search process: ", fErr)
 		} else {

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, "]")