frontend: Trigger the main thread after putting a connection back in the list.

Else, we'd have pauses of up to a second (select timeout) between processing
subsequent requests from a client because the main thread didn't notice that
an open connection was put back into the waiting queue.

diff --git a/src/frontend/sock.c b/src/frontend/sock.c
index 1827886628ae6236e991251e6b1d8ecd9a5ab34c..5279cbae84fd44d1c05623537a1bbf468860653b 100644 (file)
--- a/src/frontend/sock.c
+++ b/src/frontend/sock.c
@@ -65,6 +65,7 @@
 
 #include <pwd.h>
 
+#include <fcntl.h>
 #include <netdb.h>
 #include <libgen.h>
 #include <pthread.h>
@@ -93,7 +94,14 @@ struct sdb_fe_socket {
        listener_t *listeners;
        size_t listeners_num;
 
+       /* list of open, idle connections; active connections will be passed on to
+        * the connection handler threads which place them back after handling
+        * pending actions; the trigger pipe is used to notify the main thread
+        * after adding a connection (back) to the list */
        sdb_llist_t *open_connections;
+       int trigger[2];
+#define TRIGGER_READ 0
+#define TRIGGER_WRITE 1
 
        /* channel used for communication between main
         * and connection handler threads */
@@ -496,6 +504,7 @@ connection_handler(void *data)
                                        "connection %s to list of open connections",
                                        SDB_OBJ(conn)->name);
                }
+               write(sock->trigger[TRIGGER_WRITE], "", 1);
 
                /* pass ownership back to list; or destroy in case of an error */
                sdb_object_deref(SDB_OBJ(conn));
@@ -575,16 +584,44 @@ sdb_fe_socket_t *
 sdb_fe_sock_create(void)
 {
        sdb_fe_socket_t *sock;
+       int flags;
 
        sock = calloc(1, sizeof(*sock));
        if (! sock)
                return NULL;
+       sock->trigger[TRIGGER_READ] = sock->trigger[TRIGGER_WRITE] = -1;
 
        sock->open_connections = sdb_llist_create();
        if (! sock->open_connections) {
                sdb_fe_sock_destroy(sock);
                return NULL;
        }
+
+       if (pipe(sock->trigger)) {
+               char errbuf[1024];
+               sdb_log(SDB_LOG_ERR, "frontend: Failed to create pipe: %s",
+                               sdb_strerror(errno, errbuf, sizeof(errbuf)));
+               sdb_fe_sock_destroy(sock);
+               return NULL;
+       }
+       /* TODO: Can we do a zero-byte write as well to trigger select()?
+        * Linux does not seem to support the I_SWROPT ioctl on a pipe. */
+       flags = fcntl(sock->trigger[TRIGGER_WRITE], F_GETFL);
+       if (fcntl(sock->trigger[TRIGGER_WRITE], F_SETFL, flags | O_NONBLOCK)) {
+               char errbuf[1024];
+               sdb_log(SDB_LOG_ERR, "frontend: Failed to switch pipe to non-blocking "
+                               "mode: %s", sdb_strerror(errno, errbuf, sizeof(errbuf)));
+               sdb_fe_sock_destroy(sock);
+               return NULL;
+       }
+       flags = fcntl(sock->trigger[TRIGGER_READ], F_GETFL);
+       if (fcntl(sock->trigger[TRIGGER_READ], F_SETFL, flags | O_NONBLOCK)) {
+               char errbuf[1024];
+               sdb_log(SDB_LOG_ERR, "frontend: Failed to switch pipe to non-blocking "
+                               "mode: %s", sdb_strerror(errno, errbuf, sizeof(errbuf)));
+               sdb_fe_sock_destroy(sock);
+               return NULL;
+       }
        return sock;
 } /* sdb_fe_sock_create */
 
@@ -596,6 +633,12 @@ sdb_fe_sock_destroy(sdb_fe_socket_t *sock)
 
        socket_clear(sock);
 
+       if (sock->trigger[TRIGGER_WRITE] >= 0)
+               close(sock->trigger[TRIGGER_WRITE]);
+       if (sock->trigger[TRIGGER_READ] >= 0)
+               close(sock->trigger[TRIGGER_READ]);
+       sock->trigger[TRIGGER_READ] = sock->trigger[TRIGGER_WRITE] = -1;
+
        sdb_llist_destroy(sock->open_connections);
        sock->open_connections = NULL;
        free(sock);
@@ -694,6 +737,7 @@ sdb_fe_sock_listen_and_serve(sdb_fe_socket_t *sock, sdb_fe_loop_t *loop)
                FD_ZERO(&exceptions);
 
                ready = sockets;
+               FD_SET(sock->trigger[TRIGGER_READ], &ready);
 
                iter = sdb_llist_get_iter(sock->open_connections);
                if (! iter) {
@@ -734,6 +778,12 @@ sdb_fe_sock_listen_and_serve(sdb_fe_socket_t *sock, sdb_fe_loop_t *loop)
                else if (! n)
                        continue;
 
+               if (FD_ISSET(sock->trigger[TRIGGER_READ], &ready)) {
+                       char buf[1024];
+                       while (read(sock->trigger[TRIGGER_READ], buf, sizeof(buf)) > 0)
+                               /* do nothing */;
+               }
+
                /* handle new and open connections */
                if (socket_handle_incoming(sock, &ready, &exceptions))
                        break;