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 <unistd.h>
 #include <SDL2/SDL_thread.h>
 #include <SDL2/SDL_timer.h>
 #include <SDL2/SDL_platform.h>
@@ -318,12 +319,14 @@ 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
@@ -335,14 +338,10 @@ 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);
-    }
+
+    // wake up any net_select_interruptible()
+    close(server->pipe_intr[1]);
+
     LOGD("Server terminated");
     return 0;
 }
@@ -367,35 +366,36 @@ server_start(struct server *server, const char *serial,
         goto error1;
     }
 
-    // server will connect to our server socket
-    server->process = execute_server(server, params);
-    if (server->process == PROCESS_NONE) {
+    bool ok = net_pipe(server->pipe_intr);
+    if (!ok) {
+        perror("pipe");
         goto error2;
     }
 
-    // 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 will connect to our server socket
+    server->process = execute_server(server, params);
+    if (server->process == PROCESS_NONE) {
+        goto error3;
+    }
+
     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;
+        goto error3;
     }
 
     server->tunnel_enabled = true;
 
     return true;
 
+error3:
+    close(server->pipe_intr[0]);
+    close(server->pipe_intr[1]);
 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);
+        close_socket(&server->server_socket);
     }
     disable_tunnel(server);
 error1:
@@ -406,23 +406,34 @@ error1:
 bool
 server_connect_to(struct server *server) {
     if (!server->tunnel_forward) {
+        bool acceptable = net_select_interruptible(server->server_socket,
+                                                   server->pipe_intr[0]);
+        if (!acceptable) {
+            // the process died, accept() would never succeed
+            return false;
+        }
+
         server->video_socket = net_accept(server->server_socket);
         if (server->video_socket == INVALID_SOCKET) {
             return false;
         }
 
+        acceptable = net_select_interruptible(server->server_socket,
+                                              server->pipe_intr[0]);
+        if (!acceptable) {
+            // the process died, accept() would never succeed
+            return false;
+        }
         server->control_socket = net_accept(server->server_socket);
         if (server->control_socket == INVALID_SOCKET) {
             // the video_socket will be cleaned up on destroy
             return false;
         }
 
+        close(server->pipe_intr[0]);
+
         // we don't need the server socket anymore
-        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()
-        }
+        close_socket(&server->server_socket);
     } else {
         uint32_t attempts = 100;
         uint32_t delay = 100; // ms
@@ -449,15 +460,14 @@ server_connect_to(struct server *server) {
 
 void
 server_stop(struct server *server) {
-    if (server->server_socket != INVALID_SOCKET
-            && SDL_AtomicCAS(&server->server_socket_closed, 0, 1)) {
-        close_socket(server->server_socket);
+    if (server->server_socket != INVALID_SOCKET) {
+        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);

app/src/server.h

@@ -3,7 +3,6 @@
 
 #include <stdbool.h>
 #include <stdint.h>
-#include <SDL2/SDL_atomic.h>
 #include <SDL2/SDL_thread.h>
 
 #include "config.h"
@@ -15,7 +14,7 @@ struct server {
     char *serial;
     process_t process;
     SDL_Thread *wait_server_thread;
-    SDL_atomic_t server_socket_closed;
+    int pipe_intr[2]; // to wake up blocking accept() on process exit
     socket_t server_socket; // only used if !tunnel_forward
     socket_t video_socket;
     socket_t control_socket;
@@ -28,8 +27,6 @@ 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, \

app/src/util/net.c

@@ -1,16 +1,22 @@
 #include "net.h"
 
+#include <assert.h>
+#include <errno.h>
 #include <stdio.h>
 #include <SDL2/SDL_platform.h>
 
 #include "config.h"
+#include "common.h"
 #include "log.h"
 
 #ifdef __WINDOWS__
+# include <io.h>
+# include <winsock2.h>
   typedef int socklen_t;
 #else
-# include <sys/types.h>
+# include <sys/select.h>
 # include <sys/socket.h>
+# include <sys/types.h>
 # include <netinet/in.h>
 # include <arpa/inet.h>
 # include <unistd.h>
@@ -145,3 +151,38 @@ net_close(socket_t socket) {
     return !close(socket);
 #endif
 }
+
+bool
+net_select_interruptible(int fd, int fd_intr) {
+    fd_set rfds;
+
+    FD_ZERO(&rfds);
+    FD_SET(fd, &rfds);
+    FD_SET(fd_intr, &rfds);
+
+    int nfds = MAX(fd, fd_intr) + 1;
+
+    // use select() because it's available on supported platforms
+    int r = select(nfds, &rfds, NULL, NULL, NULL);
+    if (r == -1) {
+        // failure
+        return false;
+    }
+    assert(r > 0);
+    if (FD_ISSET(fd_intr, &rfds)) {
+        // interrupted is set
+        return false;
+    }
+
+    assert(FD_ISSET(fd, &rfds));
+    return true;
+}
+
+bool
+net_pipe(int fds[static 2]) {
+#ifdef __WINDOWS__
+    return !_pipe(fds, 4096, 0);
+#else
+    return !pipe(fds);
+#endif
+}

app/src/util/net.h

@@ -54,4 +54,12 @@ net_shutdown(socket_t socket, int how);
 bool
 net_close(socket_t socket);
 
+// wait for fd or fd_intr to be readable
+// return true if fd is readable and fd_intr is not
+bool
+net_select_interruptible(int fd, int fd_intr);
+
+bool
+net_pipe(int fd[static 2]);
+
 #endif