1 files changed, 36 insertions, 3 deletions

diff --git a/src/common/compat_threads.c b/src/common/compat_threads.c
index 98bdbbcf5e..024c627cf1 100644
--- a/src/common/compat_threads.c
+++ b/src/common/compat_threads.c
@@ -40,6 +40,7 @@ tor_mutex_free(tor_mutex_t *m)
   tor_free(m);
 }
 
+/** Allocate and return a new condition variable. */
 tor_cond_t *
 tor_cond_new(void)
 {
@@ -48,6 +49,8 @@ tor_cond_new(void)
     tor_free(cond);
   return cond;
 }
+
+/** Free all storage held in <b>c</b>. */
 void
 tor_cond_free(tor_cond_t *c)
 {
@@ -140,13 +143,16 @@ sock_drain(tor_socket_t fd)
   return 0;
 }
 
-/** Allocate a new set of alert sockets. DOCDOC */
+/** Allocate a new set of alert sockets, and set the appropriate function
+ * pointers, in <b>socks_out</b>. */
 int
 alert_sockets_create(alert_sockets_t *socks_out)
 {
   tor_socket_t socks[2];
 
 #ifdef HAVE_EVENTFD
+  /* First, we try the Linux eventfd() syscall.  This gives a 64-bit counter
+   * associated with a single file descriptor. */
 #if defined(EFD_CLOEXEC) && defined(EFD_NONBLOCK)
   socks[0] = eventfd(0, EFD_CLOEXEC|EFD_NONBLOCK);
 #else
@@ -171,6 +177,8 @@ alert_sockets_create(alert_sockets_t *socks_out)
 #endif
 
 #ifdef HAVE_PIPE2
+  /* Now we're going to try pipes. First type the pipe2() syscall, if we
+   * have it, so we can save some calls... */
   if (pipe2(socks, O_NONBLOCK|O_CLOEXEC) == 0) {
     socks_out->read_fd = socks[0];
     socks_out->write_fd = socks[1];
@@ -181,6 +189,8 @@ alert_sockets_create(alert_sockets_t *socks_out)
 #endif
 
 #ifdef HAVE_PIPE
+  /* Now try the regular pipe() syscall.  Pipes have a bit lower overhead than
+   * socketpairs, fwict. */
   if (pipe(socks) == 0) {
     if (fcntl(socks[0], F_SETFD, FD_CLOEXEC) < 0 ||
         fcntl(socks[1], F_SETFD, FD_CLOEXEC) < 0 ||
@@ -198,12 +208,35 @@ alert_sockets_create(alert_sockets_t *socks_out)
   }
 #endif
 
+  /* If nothing else worked, fall back on socketpair(). */
   if (tor_socketpair(AF_UNIX, SOCK_STREAM, 0, socks) == 0) {
-    set_socket_nonblocking(socks[0]);
-    set_socket_nonblocking(socks[1]);
+    if (set_socket_nonblocking(socks[0]) < 0 ||
+        set_socket_nonblocking(socks[1])) {
+      tor_close_socket(socks[0]);
+      tor_close_socket(socks[1]);
+      return -1;
+    }
+    socks_out->read_fd = socks[0];
+    socks_out->write_fd = socks[1];
     socks_out->alert_fn = sock_alert;
     socks_out->drain_fn = sock_drain;
     return 0;
   }
   return -1;
 }
+
+/** Close the sockets in <b>socks</b>. */
+void
+alert_sockets_close(alert_sockets_t *socks)
+{
+  if (socks->alert_fn == sock_alert) {
+    /* they are sockets. */
+    tor_close_socket(socks->read_fd);
+    tor_close_socket(socks->write_fd);
+  } else {
+    close(socks->read_fd);
+    if (socks->write_fd != socks->read_fd)
+      close(socks->write_fd);
+  }
+  socks->read_fd = socks->write_fd = -1;
+}