Do not warn on terminating the server

If the server is already dead, terminating it fails. This is expected.

app/src/server.c

@@ -5,6 +5,7 @@
 #include <inttypes.h>
 #include <libgen.h>
 #include <stdio.h>
+#include <SDL2/SDL_thread.h>
 #include <SDL2/SDL_timer.h>
 #include <SDL2/SDL_platform.h>
 
@@ -317,14 +318,12 @@ connect_to_server(uint16_t port, uint32_t attempts, uint32_t delay) {
 }
 
 static void
-close_socket(socket_t *socket) {
-    assert(*socket != INVALID_SOCKET);
-    net_shutdown(*socket, SHUT_RDWR);
-    if (!net_close(*socket)) {
+close_socket(socket_t socket) {
+    assert(socket != INVALID_SOCKET);
+    net_shutdown(socket, SHUT_RDWR);
+    if (!net_close(socket)) {
         LOGW("Could not close socket");
-        return;
     }
-    *socket = INVALID_SOCKET;
 }
 
 void
@@ -332,6 +331,22 @@ server_init(struct server *server) {
     *server = (struct server) SERVER_INITIALIZER;
 }
 
+static int
+run_wait_server(void *data) {
+    struct server *server = data;
+    cmd_simple_wait(server->process, NULL); // ignore exit code
+    // no need for synchronization, server_socket is initialized before this
+    // thread was created
+    if (server->server_socket != INVALID_SOCKET
+            && SDL_AtomicCAS(&server->server_socket_closed, 0, 1)) {
+        // On Linux, accept() is unblocked by shutdown(), but on Windows, it is
+        // unblocked by closesocket(). Therefore, call both (close_socket()).
+        close_socket(server->server_socket);
+    }
+    LOGD("Server terminated");
+    return 0;
+}
+
 bool
 server_start(struct server *server, const char *serial,
              const struct server_params *params) {
@@ -345,30 +360,47 @@ server_start(struct server *server, const char *serial,
     }
 
     if (!push_server(serial)) {
-        SDL_free(server->serial);
-        return false;
+        goto error1;
     }
 
     if (!enable_tunnel_any_port(server, params->port_range)) {
-        SDL_free(server->serial);
-        return false;
+        goto error1;
     }
 
     // server will connect to our server socket
     server->process = execute_server(server, params);
-
     if (server->process == PROCESS_NONE) {
-        if (!server->tunnel_forward) {
-            close_socket(&server->server_socket);
+        goto error2;
     }
-        disable_tunnel(server);
-        SDL_free(server->serial);
-        return false;
+
+    // If the server process dies before connecting to the server socket, then
+    // the client will be stuck forever on accept(). To avoid the problem, we
+    // must be able to wake up the accept() call when the server dies. To keep
+    // things simple and multiplatform, just spawn a new thread waiting for the
+    // server process and calling shutdown()/close() on the server socket if
+    // necessary to wake up any accept() blocking call.
+    server->wait_server_thread =
+        SDL_CreateThread(run_wait_server, "wait-server", server);
+    if (!server->wait_server_thread) {
+        cmd_terminate(server->process);
+        cmd_simple_wait(server->process, NULL); // ignore exit code
+        goto error2;
     }
 
     server->tunnel_enabled = true;
 
     return true;
+
+error2:
+    if (!server->tunnel_forward) {
+        // the wait server thread is not started, SDL_AtomicSet() is sufficient
+        SDL_AtomicSet(&server->server_socket_closed, 1);
+        close_socket(server->server_socket);
+    }
+    disable_tunnel(server);
+error1:
+    SDL_free(server->serial);
+    return false;
 }
 
 bool
@@ -386,7 +418,11 @@ server_connect_to(struct server *server) {
         }
 
         // we don't need the server socket anymore
-        close_socket(&server->server_socket);
+        if (SDL_AtomicCAS(&server->server_socket_closed, 0, 1)) {
+            // close it from here
+            close_socket(server->server_socket);
+            // otherwise, it is closed by run_wait_server()
+        }
     } else {
         uint32_t attempts = 100;
         uint32_t delay = 100; // ms
@@ -413,29 +449,27 @@ server_connect_to(struct server *server) {
 
 void
 server_stop(struct server *server) {
-    if (server->server_socket != INVALID_SOCKET) {
-        close_socket(&server->server_socket);
+    if (server->server_socket != INVALID_SOCKET
+            && SDL_AtomicCAS(&server->server_socket_closed, 0, 1)) {
+        close_socket(server->server_socket);
     }
     if (server->video_socket != INVALID_SOCKET) {
-        close_socket(&server->video_socket);
+        close_socket(server->video_socket);
     }
     if (server->control_socket != INVALID_SOCKET) {
-        close_socket(&server->control_socket);
+        close_socket(server->control_socket);
     }
 
     assert(server->process != PROCESS_NONE);
 
-    if (!cmd_terminate(server->process)) {
-        LOGW("Could not terminate server");
-    }
-
-    cmd_simple_wait(server->process, NULL); // ignore exit code
-    LOGD("Server terminated");
+    cmd_terminate(server->process);
 
     if (server->tunnel_enabled) {
         // ignore failure
         disable_tunnel(server);
     }
+
+    SDL_WaitThread(server->wait_server_thread, NULL);
 }
 
 void

app/src/server.h

@@ -3,6 +3,8 @@
 
 #include <stdbool.h>
 #include <stdint.h>
+#include <SDL2/SDL_atomic.h>
+#include <SDL2/SDL_thread.h>
 
 #include "config.h"
 #include "command.h"
@@ -12,6 +14,8 @@
 struct server {
     char *serial;
     process_t process;
+    SDL_Thread *wait_server_thread;
+    SDL_atomic_t server_socket_closed;
     socket_t server_socket; // only used if !tunnel_forward
     socket_t video_socket;
     socket_t control_socket;
@@ -24,6 +28,8 @@ struct server {
 #define SERVER_INITIALIZER { \
     .serial = NULL, \
     .process = PROCESS_NONE, \
+    .wait_server_thread = NULL, \
+    .server_socket_closed = {0}, \
     .server_socket = INVALID_SOCKET, \
     .video_socket = INVALID_SOCKET, \
     .control_socket = INVALID_SOCKET, \