Merge pull request #1210 from nkolban/add-select-dtrans-socket

Addition of optional select() for debug transport

AUTHORS.rst

@@ -78,6 +78,7 @@ bugs, provided ideas, etc; roughly in order of appearance):
 * Michael Drake (https://github.com/tlsa)
 * https://github.com/chris-y
 * Laurent Zubiaur (https://github.com/lzubiaur)
+* Neil Kolban (https://github.com/nkolban)
 
 If you are accidentally missing from this list, send me an e-mail
 (``sami.vaarala@iki.fi``) and I'll fix the omission.

examples/debug-trans-socket/duk_trans_socket_unix.c

@@ -5,12 +5,27 @@
  *  After that data is just passed through.
  */
 
+/*
+ *  The select() vs poll() story.  The two system calls called
+ *  "select()" and "poll()" are similar but not necessarily available
+ *  on all platforms.  The default implementation is to use "poll()"
+ *  but we can switch that by defining "USE_SELECT" within this
+ *  file.  For example:
+ *
+ *  #define USE_SELECT
+ *
+ *  If set, instead of leveraging "poll()", this code will leverage
+ *  "select()".   Discussions on "poll()" vs "select()" can be read
+ *  about here: https://daniel.haxx.se/docs/poll-vs-select.html
+ */
 #include <stdio.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <netinet/in.h>
 #include <unistd.h>
+#if !defined(USE_SELECT)
 #include <poll.h>
+#endif /* ! USE_SELECT */
 #include <errno.h>
 #include "duktape.h"
 
@@ -253,8 +268,12 @@ duk_size_t duk_trans_socket_write_cb(void *udata, const char *buffer, duk_size_t
 }
 
 duk_size_t duk_trans_socket_peek_cb(void *udata) {
+#if defined(USE_SELECT)
+	fd_set rfds;
+#else /* USE_SELECT */
 	struct pollfd fds[1];
 	int poll_rc;
+#endif /* USE_SELECT */
 
 	(void) udata;  /* not needed by the example */
 
@@ -266,7 +285,20 @@ duk_size_t duk_trans_socket_peek_cb(void *udata) {
 	if (client_sock < 0) {
 		return 0;
 	}
-
+#if defined(USE_SELECT)
+	FD_ZERO(&rfds);
+	FD_SET(client_sock, &rfds);
+	struct timeval tm;
+	tm.tv_sec = tm.tv_usec = 0;
+	int select_rc = select(client_sock + 1, &rfds, NULL, NULL, &tm);
+	if (select_rc == 0) {
+		return 0;
+	}
+	if (select_rc == 1) {
+		return 1;
+	}
+	goto fail;
+#else /* USE_SELECT */
 	fds[0].fd = client_sock;
 	fds[0].events = POLLIN;
 	fds[0].revents = 0;
@@ -287,7 +319,7 @@ duk_size_t duk_trans_socket_peek_cb(void *udata) {
 	} else {
 		return 1;  /* something to read */
 	}
-
+#endif /* USE_SELECT */
  fail:
 	if (client_sock >= 0) {
 		(void) close(client_sock);