ql: rewrite to non-blocking I/O

1 files changed, 77 insertions, 24 deletions

diff --git a/src/ql.c b/src/ql.c
index e759cb0..167f7a8 100644
--- a/src/ql.c
+++ b/src/ql.c
@@ -11,6 +11,7 @@
 #include <fcntl.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 struct ql_ctx {
 	char *printer;
@@ -19,29 +20,53 @@ struct ql_ctx {
 
 #define ESC 0x1b
 
-#define NUM_STATUS_READ_RETRIES 100
+#define STATUS_READ_TIMEOUT 5	/* seconds */
 
 #define full_write(fd, buf) (retry_write(fd, buf, sizeof(buf)) == (ssize_t)sizeof(buf))
 
 ssize_t retry_write(int fd, const char *buf, size_t len)
 {
 	size_t written = 0;
+
+	int retval;
+	fd_set wfds;
+	struct timeval tv;
+
 	while (written != len) {
-		ssize_t n = write(fd, buf + written, len - written);
-		if (n == -1) {
-			if (errno == EAGAIN || errno == EINTR)
-				continue;
-			else
-				break;
-		} else
-			written += n;
+		FD_ZERO(&wfds);
+		FD_SET(fd, &wfds);
+
+		tv.tv_sec = 5;
+		tv.tv_usec = 0;
+
+		retval = select(fd + 1, NULL, &wfds, NULL, &tv);
+		if (retval == -1)
+			perror("select()");
+		else if (FD_ISSET(fd, &wfds)) {
+			ssize_t n = write(fd, buf + written, len - written);
+			if (n == -1) {
+				if (errno == EAGAIN || errno == EINTR)
+					continue;
+				else
+					break;
+			} else
+				written += n;
+		}
 	}
 	return written;
 }
 
+static void get_mono_time(struct timespec *tp)
+{
+	if (clock_gettime(CLOCK_MONOTONIC, tp) == -1) {
+		perror("clock_gettime");
+		exit(EXIT_FAILURE);
+	}
+}
+
 ql_ctx_t ql_open(const char *printer)
 {
-	int fd = open(printer, O_RDWR);
+	int fd = open(printer, O_RDWR | O_NONBLOCK);
 	if (fd < 0)
 		return NULL;
 
@@ -78,20 +103,48 @@ bool ql_request_status(ql_ctx_t ctx)
 
 bool ql_read_status(ql_ctx_t ctx, ql_status_t * status)
 {
-	for (int i = 0; i < NUM_STATUS_READ_RETRIES; ++i) {
-		int ret = read(ctx->fd, status, sizeof(*status));
-		if (ret == 32)
-			return true;
-		else if ((ret == 0)	// "no data yet, too bad we just eof'd your fd, sucker"
-			 || (ret == -1 && errno == EBADF))	// in case we messed up, somehow
-		{
-			close(ctx->fd);
-			ctx->fd = open(ctx->printer, O_RDWR);
-			if (ctx->fd < 0)
-				return false;
-		} else if (ret == -1 && (errno != EAGAIN || errno != EINTR))
-			return false;	// non-recoverable
-	}
+	int retval;
+	fd_set rfds;
+	struct timeval tv;
+	struct timespec tp_begin;
+	struct timespec tp_now;
+
+	get_mono_time(&tp_begin);
+
+	/* If select(2) selects returns early, then the outer loop calls
+	 * usleep(3) and tries again, until the timeout is reached. */
+	int i = 0;
+	do {
+		i++;
+
+		FD_ZERO(&rfds);
+		FD_SET(ctx->fd, &rfds);
+
+		if (tp_now.tv_sec == 0) {
+			tv.tv_sec = STATUS_READ_TIMEOUT;
+		} else {
+			tv.tv_sec = tp_begin.tv_sec + STATUS_READ_TIMEOUT - tp_now.tv_sec;
+		}
+		tv.tv_usec = 0;
+
+		retval = select(ctx->fd + 1, &rfds, NULL, NULL, &tv);
+
+		if (retval == -1) {
+			perror("select()");
+		} else if (retval == 0) {
+			break;	/* timeout */
+		} else if (FD_ISSET(ctx->fd, &rfds)) {
+			int ret = read(ctx->fd, status, sizeof(*status));
+			if (ret == 32) {
+				return true;
+			} else {
+				usleep(i * 5000);	/* i * 5 ms */
+			}
+		}
+
+		get_mono_time(&tp_now);
+	} while (tp_now.tv_sec - tp_begin.tv_sec < STATUS_READ_TIMEOUT);
+
 	errno = ETIME;
 	return false;
 }