Init

usr.lib/libcurses/screen/select.c

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+#ifndef lint
+static	char sccsid[] = "@(#)select.c 1.1 94/10/31 SMI"; /* from S5R2 1.1 */
+#endif
+
+/*
+ * Code for various kinds of delays.  Most of this is nonportable and
+ * requires various enhancements to the operating system, so it won't
+ * work on all systems.  It is included in curses to provide a portable
+ * interface, and so curses itself can use it for function keys.
+ */
+
+#include "curses.ext"
+#include <signal.h>
+
+#define NAPINTERVAL 100
+
+/* From early specs - this may change by 4.2BSD */
+struct _timeval {
+	long tv_sec;
+	long tv_usec;
+};
+
+#ifdef FIONREAD
+# ifndef TIOCREMOTE
+/*
+ * Decide if we can emulate select but don't have it.  This is
+ * intended to be true only on 4.1BSD, not 4.2BSD or USG.
+ */
+#  define NEEDSELECT
+# endif
+#endif
+
+#ifdef NEEDSELECT
+/*
+ * Emulation of 4.2BSD select system call.  This is somewhat crude but
+ * better than nothing.  We do FIONREAD on each fd, and if we have to
+ * wait we use nap to avoid a busy wait.  The resolution of the nap
+ * will hurt response - so will the fact that we ignore the write fds.
+ * If we are simulating nap with a 1 second sleep, this will be very poor.
+ *
+ * nfds is the number of fds to check - this is usually 20.
+ * prfds is a pointer to a bit vector of file descriptors - in the case
+ *	where nfds < 32, prfds points to an integer, where bit 1<<fd
+ *	is 1 if we are supposed to check file descriptor fd.
+ * pwfds is like prfds but for write checks instead of read checks.
+ * ms is the max number of milliseconds to wait before returning failure.
+ * The value returned is the number of file descriptors ready for input.
+ * The bit vectors are updated in place.
+ */
+
+int
+select(nfds, prfds, pwfds, pefds, timeout)
+register int nfds;
+int *prfds, *pwfds, *pefds;
+struct _timeval *timeout;
+{
+	register int fd;
+	register int rfds = *prfds;
+	register int n;
+	int nwaiting, rv = 0;
+	long ms = timeout->tv_sec * 1000 + timeout->tv_usec / 1000;
+
+	for (;;) {
+		/* check the fds */
+		for (fd=0; fd<nfds; fd++)
+			if (1<<fd & rfds) {
+				ioctl(fd, FIONREAD, &nwaiting);
+				if (nwaiting > 0) {
+					rv++;
+				} else
+					*prfds &= ~(1<<fd);
+			}
+		if (rv)
+			return rv;
+
+		/* Nothing ready.  Should we give up? */
+		if (ms <= 0)
+			return 0;
+
+		*prfds = rfds;	/* we clobbered it, so restore. */
+
+		/* Wait a bit */
+		n = NAPINTERVAL;
+		if (ms < NAPINTERVAL)
+			n = ms;
+		ms -= n;
+		napms(n);
+	}
+}
+#else
+#ifndef FIONREAD
+int
+select(nfds, prfds, pwfds, pefds, ms)
+register int nfds;
+int *prfds, *pwfds, *pefds;
+struct _timeval *ms;
+{
+	/* Can't do it, but at least compile right */
+	return ERR;
+}
+#endif FIONREAD
+#endif NEEDSELECT