Add a new option to enable/disable IOCP support

changes/bufferevent-support

@@ -6,4 +6,7 @@
      flag.  Using this feature will make our networking code more flexible,
      lets us stack layers on each other, and let us use more efficient
      zero-copy transports where available.
+   - As an experimental feature, when using the "bufferevents" buffered
+     IO backend, Tor can try to use Windows's IOCP networking API.  This
+     is off by default.  To turn it on, add "DisableIOCP 0" to your torrc.
 

doc/tor.1.txt

@@ -397,6 +397,11 @@ Other options can be specified either on the command-line (--option
     networkstatus. This is an advanced option; you generally shouldn't have
     to mess with it. (Default: not set.)
 
+**DisableIOCP** **0**|**1**::
+    If Tor was built to use the Libevent's "bufferevents" networking code
+    and you're running on Windows, setting this option to 1 will tell Libevent
+    not to use the Windows IOCP networking API.  (Default: 1)
+
 CLIENT OPTIONS
 --------------
 

src/common/compat_libevent.c

@@ -159,7 +159,7 @@ struct event_base *the_event_base = NULL;
 
 /** Initialize the Libevent library and set up the event base. */
 void
-tor_libevent_initialize(void)
+tor_libevent_initialize(tor_libevent_cfg *torcfg)
 {
   tor_assert(the_event_base == NULL);
 
@@ -171,7 +171,21 @@ tor_libevent_initialize(void)
 #endif
 
 #ifdef HAVE_EVENT2_EVENT_H
-  the_event_base = event_base_new();
+  {
+    struct event_config *cfg = event_config_new();
+
+#if defined(MS_WINDOWS) && defined(USE_BUFFEREVENTS)
+    if (! torcfg->disable_iocp)
+      event_config_set_flag(cfg, EVENT_BASE_FLAG_STARTUP_IOCP);
+#endif
+
+#if defined(LIBEVENT_VERSION_NUMBER) && LIBEVENT_VERSION_NUMBER >= V(2,0,7)
+    if (torcfg->num_cpus > 0)
+      event_config_set_num_cpus_hint(cfg, torcfg->num_cpus);
+#endif
+
+    the_event_base = event_base_new_with_config(cfg);
+  }
 #else
   the_event_base = event_init();
 #endif

src/common/compat_libevent.h

@@ -56,7 +56,12 @@ struct timeval;
 int tor_event_base_loopexit(struct event_base *base, struct timeval *tv);
 #endif
 
-void tor_libevent_initialize(void);
+typedef struct tor_libevent_cfg {
+  int disable_iocp;
+  int num_cpus;
+} tor_libevent_cfg;
+
+void tor_libevent_initialize(tor_libevent_cfg *cfg);
 struct event_base *tor_libevent_get_base(void);
 const char *tor_libevent_get_method(void);
 void tor_check_libevent_version(const char *m, int server,

src/or/config.c

@@ -224,6 +224,7 @@ static config_var_t _option_vars[] = {
   V(DirReqStatistics,            BOOL,     "0"),
   VAR("DirServer",               LINELIST, DirServers, NULL),
   V(DisableAllSwap,              BOOL,     "0"),
+  V(DisableIOCP,                 BOOL,     "1"),
   V(DNSPort,                     UINT,     "0"),
   V(DNSListenAddress,            LINELIST, NULL),
   V(DownloadExtraInfo,           BOOL,     "0"),
@@ -554,7 +555,7 @@ static int is_listening_on_low_port(uint16_t port_option,
 
 static uint64_t config_parse_memunit(const char *s, int *ok);
 static int config_parse_interval(const char *s, int *ok);
-static void init_libevent(void);
+static void init_libevent(const or_options_t *options);
 static int opt_streq(const char *s1, const char *s2);
 
 /** Magic value for or_options_t. */
@@ -955,7 +956,7 @@ options_act_reversible(or_options_t *old_options, char **msg)
     /* Set up libevent.  (We need to do this before we can register the
      * listeners as listeners.) */
     if (running_tor && !libevent_initialized) {
-      init_libevent();
+      init_libevent(options);
       libevent_initialized = 1;
     }
 
@@ -4895,9 +4896,12 @@ config_parse_interval(const char *s, int *ok)
  * Initialize the libevent library.
  */
 static void
-init_libevent(void)
+init_libevent(const or_options_t *options)
 {
   const char *badness=NULL;
+  tor_libevent_cfg cfg;
+
+  tor_assert(options);
 
   configure_libevent_logging();
   /* If the kernel complains that some method (say, epoll) doesn't
@@ -4907,7 +4911,11 @@ init_libevent(void)
 
   tor_check_libevent_header_compatibility();
 
-  tor_libevent_initialize();
+  memset(&cfg, 0, sizeof(cfg));
+  cfg.disable_iocp = options->DisableIOCP;
+  cfg.num_cpus = options->NumCpus;
+
+  tor_libevent_initialize(&cfg);
 
   suppress_libevent_log_msg(NULL);
 

src/or/or.h

@@ -2892,6 +2892,10 @@ typedef struct {
    */
   double CircuitPriorityHalflife;
 
+  /** If true, do not enable IOCP on windows with bufferevents, even if
+   * we think we could. */
+  int DisableIOCP;
+
 } or_options_t;
 
 /** Persistent state for an onion router, as saved to disk. */