Be more graceful with too many connections.

Fixes bug beanstalkd#587.

beanstalkd.c

@@ -10,6 +10,7 @@
 #include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/resource.h>
 
 #include "conn.h"
 #include "net.h"
@@ -649,6 +650,7 @@ h_accept(const int fd, const short which, struct event *ev)
  cfd = accept(fd, &addr, &addrlen);
  if (cfd == -1) {
  if (errno != EAGAIN && errno != EWOULDBLOCK) twarn("accept()");
+ if (errno == EMFILE) brake();
  return;
  }
 
@@ -659,21 +661,20 @@ h_accept(const int fd, const short which, struct event *ev)
  if (r < 0) return twarn("setting O_NONBLOCK"), close(cfd), v();
 
  c = make_conn(cfd, STATE_WANTCOMMAND);
- if (!c) return twarnx("make_conn() failed"), close(cfd), v();
+ if (!c) return twarnx("make_conn() failed"), close(cfd), brake();
 
  dprintf("accepted conn, fd=%d\n", cfd);
  r = conn_set_evq(c, EV_READ | EV_PERSIST, (evh) h_conn);
- if (r == -1) return twarnx("conn_set_evq() failed"), close(cfd), v();
+ if (r == -1) return twarnx("conn_set_evq() failed"), close(cfd), brake();
 }
 
 int
 main(int argc, char **argv)
 {
- int listen_socket;
- struct event listen_evq;
+ int r;
 
- listen_socket = make_server_socket(HOST, PORT);
- if (listen_socket == -1) twarnx("make_server_socket()"), exit(111);
+ r = make_server_socket(HOST, PORT);
+ if (r == -1) twarnx("make_server_socket()"), exit(111);
 
  prot_init();
 #ifndef DEBUG
@@ -682,9 +683,9 @@ main(int argc, char **argv)
  event_init();
  set_sig_handlers();
 
- event_set(&listen_evq, listen_socket, EV_READ | EV_PERSIST, (evh) h_accept, &listen_evq);
- event_add(&listen_evq, NULL);
+ unbrake((evh) h_accept);
 
  event_dispatch();
+ twarnx("got here for some reason");
  return 0;
 }

conn.c

@@ -169,6 +169,7 @@ conn_close(conn c)
 
  cur_conn_ct--; /* stats */
 
+ unbrake(NULL);
  conn_remove(c);
  conn_free(c);
 }

net.c

@@ -1,10 +1,15 @@
 /* net.c - stupid boilerplate shit that I shouldn't have to write */
 
 #include <stdio.h>
+#include <errno.h>
 
 #include "net.h"
 #include "util.h"
 
+static int listen_socket = -1;
+static struct event listen_evq;
+static evh accept_handler;
+
 int
 make_server_socket(int host, int port)
 {
@@ -38,6 +43,39 @@ make_server_socket(int host, int port)
  r = listen(fd, 1024);
  if (r == -1) return twarn("listen()"), close(fd), -1;
 
- return fd;
+ return listen_socket = fd;
+}
+
+void
+brake()
+{
+ int r;
+
+ twarnx("too many connections; putting on the brakes");
+
+ r = event_del(&listen_evq);
+ if (r == -1) twarn("event_del()");
+
+ r = listen(listen_socket, 0);
+ if (r == -1) twarn("listen()");
+}
+
+void
+unbrake(evh h)
+{
+ int r;
+
+ twarnx("releasing the brakes");
+
+ accept_handler = h ? : accept_handler;
+ event_set(&listen_evq, listen_socket, EV_READ | EV_PERSIST,
+ accept_handler, &listen_evq);
+
+ errno = 0;
+ r = event_add(&listen_evq, NULL);
+ if (r == -1) twarn("event_add()");
+
+ r = listen(listen_socket, 1024);
+ if (r == -1) twarn("listen()");
 }
 

net.h

@@ -13,4 +13,7 @@
 
 int make_server_socket(int host, int port);
 
+void brake();
+void unbrake(evh h);
+
 #endif /*net_h*/