fix: make Server.isRegistered atomic

context.go

@@ -67,7 +67,7 @@ func newContextFromRequest(request *http.Request, responseWriter http.ResponseWr
 		startedAt:      time.Now(),
 		server:         s,
 		splitPath:      s.splitPath,
-		logger:         s.logger,
+		logger:         s.logger.Load(),
 		request:        request,
 		documentRoot:   s.root,
 		responseWriter: responseWriter,

frankenphp.go

@@ -57,7 +57,7 @@ var (
 	contextKey   = contextKeyStruct{}
 	serverHeader = []string{"FrankenPHP"}
 
-	isRunning        bool
+	isRunning        atomic.Bool
 	onServerShutdown []func()
 
 	// Set default values to make Shutdown() idempotent
@@ -240,10 +240,9 @@ func calculateMaxThreads(opt *opt) (numWorkers int, _ error) {
 
 // Init starts the PHP runtime and the configured workers.
 func Init(options ...Option) error {
-	if isRunning {
+	if !isRunning.CompareAndSwap(false, true) {
 		return ErrAlreadyStarted
 	}
-	isRunning = true
 
 	// Ignore all SIGPIPE signals to prevent weird issues with systemd: https://github.com/php/frankenphp/issues/1020
 	// Docker/Moby has a similar hack: https://github.com/moby/moby/blob/d828b032a87606ae34267e349bf7f7ccb1f6495a/cmd/dockerd/docker.go#L87-L90
@@ -367,7 +366,7 @@ func Init(options ...Option) error {
 
 // Shutdown stops the workers and the PHP runtime.
 func Shutdown() {
-	if !isRunning {
+	if !isRunning.Load() {
 		return
 	}
 
@@ -387,7 +386,7 @@ func Shutdown() {
 		_ = os.RemoveAll(EmbeddedAppPath)
 	}
 
-	isRunning = false
+	isRunning.Store(false)
 	if globalLogger.Enabled(globalCtx, slog.LevelDebug) {
 		globalLogger.LogAttrs(globalCtx, slog.LevelDebug, "FrankenPHP shut down")
 	}

server.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"log/slog"
 	"net/http"
+	"sync/atomic"
 
 	"github.com/dunglas/frankenphp/internal/fastabs"
 )
@@ -15,12 +16,18 @@ type Server struct {
 	root                      string
 	splitPath                 []string
 	env                       PreparedEnv
-	logger                    *slog.Logger
 	workers                   []*worker
 	workersByPath             map[string]*worker
 	workersWithRequestMatcher []*worker
 	workerOpts                []workerOpt
-	isRegistered              bool
+
+	// registered while FrankenPHP runs with this server; read by concurrent
+	// ServeHTTP calls while Init()/Shutdown() flip it, hence atomic
+	isRegistered atomic.Bool
+
+	// atomic for the same reason: the fallback server's logger is replaced
+	// at registration time while in-flight requests may read it
+	logger atomic.Pointer[slog.Logger]
 }
 
 var (
@@ -34,18 +41,18 @@ var (
 
 func registerServers(newServers []*Server) {
 	servers = newServers
-	fallbackServer.isRegistered = true
-	fallbackServer.logger = globalLogger
+	fallbackServer.logger.Store(globalLogger)
+	fallbackServer.isRegistered.Store(true)
 	for i, s := range servers {
-		s.isRegistered = true
+		s.isRegistered.Store(true)
 		s.idx = i
 	}
 }
 
 func unregisterServers() {
-	fallbackServer.isRegistered = false
+	fallbackServer.isRegistered.Store(false)
 	for _, server := range servers {
-		server.isRegistered = false
+		server.isRegistered.Store(false)
 	}
 }
 
@@ -63,11 +70,15 @@ func NewServer(root string, splitPath []string, env map[string]string, logger *s
 		root:          root,
 		splitPath:     splitPath,
 		env:           PrepareEnv(env),
-		logger:        logger,
 		workersByPath: make(map[string]*worker),
 		workerOpts:    make([]workerOpt, 0),
 	}
 
+	if logger == nil {
+		logger = globalLogger
+	}
+	s.logger.Store(logger)
+
 	if len(s.splitPath) == 0 {
 		s.splitPath = []string{".php"}
 	}
@@ -76,10 +87,6 @@ func NewServer(root string, splitPath []string, env map[string]string, logger *s
 		s.env = PrepareEnv(nil)
 	}
 
-	if s.logger == nil {
-		s.logger = globalLogger
-	}
-
 	return s, nil
 }
 
@@ -102,7 +109,7 @@ func (s *Server) addWorker(w *worker) error {
 // The request will be scoped to the server instance that was registered via WithServer().
 // Otherwise, it is equivalent to calling ServeHTTP.
 func (s *Server) ServeHTTP(responseWriter http.ResponseWriter, request *http.Request, opts ...RequestOption) error {
-	if !s.isRegistered {
+	if !s.isRegistered.Load() {
 		return ErrNotRunning
 	}