Binding a socket makes it non-blocking by default.

Allowing primitives (currently only send/receive) to block just once
with SEXP_G_IO_BLOCK_ONCE_ERROR.

eval.c

@@ -490,6 +490,8 @@ void sexp_init_eval_context_globals (sexp ctx) {
 #if SEXP_USE_GREEN_THREADS
   sexp_global(ctx, SEXP_G_IO_BLOCK_ERROR)
     = sexp_user_exception(ctx, SEXP_FALSE, "I/O would block", SEXP_NULL);
+  sexp_global(ctx, SEXP_G_IO_BLOCK_ONCE_ERROR)
+    = sexp_user_exception(ctx, SEXP_FALSE, "I/O would block once", SEXP_NULL);
   sexp_global(ctx, SEXP_G_THREADS_FRONT) = SEXP_NULL;
   sexp_global(ctx, SEXP_G_THREADS_BACK) = SEXP_NULL;
   sexp_global(ctx, SEXP_G_THREADS_SIGNALS) = SEXP_ZERO;

include/chibi/sexp.h

@@ -1232,6 +1232,7 @@ enum sexp_context_globals {
 #endif
 #if SEXP_USE_GREEN_THREADS
   SEXP_G_IO_BLOCK_ERROR,
+  SEXP_G_IO_BLOCK_ONCE_ERROR,
   SEXP_G_THREADS_SCHEDULER,
   SEXP_G_THREADS_FRONT,
   SEXP_G_THREADS_BACK,

lib/chibi/accept.c

@@ -39,7 +39,7 @@ sexp sexp_sendto (sexp ctx, sexp self, int sock, const void* buffer, size_t len,
     f = sexp_global(ctx, SEXP_G_THREADS_BLOCKER);
     if (sexp_applicablep(f)) {
       sexp_apply2(ctx, f, sexp_make_fixnum(sock), timeout);
-      return sexp_global(ctx, SEXP_G_IO_BLOCK_ERROR);
+      return sexp_global(ctx, SEXP_G_IO_BLOCK_ONCE_ERROR);
     }
   }
 #endif
@@ -57,15 +57,24 @@ sexp sexp_recvfrom (sexp ctx, sexp self, int sock, void* buffer, size_t len, int
     f = sexp_global(ctx, SEXP_G_THREADS_BLOCKER);
     if (sexp_applicablep(f)) {
       sexp_apply2(ctx, f, sexp_make_fixnum(sock), timeout);
-      return sexp_global(ctx, SEXP_G_IO_BLOCK_ERROR);
+      return sexp_global(ctx, SEXP_G_IO_BLOCK_ONCE_ERROR);
     }
   }
 #endif
   return sexp_make_fixnum(res);
 }
 
-/* If we're listening on a socket from Scheme, we most likely want it */
+/* If we're binding or listening on a socket from Scheme, we most */
-/* to be non-blocking. */
+/* likely want it to be non-blocking. */
+
+sexp sexp_bind (sexp ctx, sexp self, int fd, struct sockaddr* addr, socklen_t addr_len) {
+  int res = bind(fd, addr, addr_len);
+#if SEXP_USE_GREEN_THREADS
+  if (res >= 0)
+    fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);
+#endif
+  return (res == 0) ? SEXP_TRUE : SEXP_FALSE;
+}
 
 sexp sexp_listen (sexp ctx, sexp self, sexp fileno, sexp backlog) {
   int fd, res;

lib/chibi/net.stub

@@ -32,7 +32,8 @@
 
 ;;> Bind a name to a socket.
 
-(define-c errno bind (fileno sockaddr int))
+(define-c sexp (bind "sexp_bind")
+  ((value ctx sexp) (value self sexp) fileno sockaddr int))
 
 ;;> Listen on a socket.
 

vm.c

@@ -883,6 +883,9 @@ static int sexp_check_type(sexp ctx, sexp a, sexp b) {
   if (sexp_exceptionp(x)) {                                 \
     if (x == sexp_global(ctx, SEXP_G_IO_BLOCK_ERROR)) {     \
       fuel = 0; ip--; goto loop;                            \
+    } else if (x == sexp_global(ctx, SEXP_G_IO_BLOCK_ONCE_ERROR)) { \
+      stack[top-i+1] = SEXP_ZERO;                                   \
+      fuel = 0; ip--; goto loop;                            \
     } else {                                                \
       top -= i;                                             \
       _ARG1 = x;                                            \