drv: do a pre-allocation to store all timestamps

This allows bigger read from the driver, which reduces the number of syscall and make the system faster Signed-off-by: Federico Vaga <federico.vaga@cern.ch>

drv: do a pre-allocation to store all timestamps
This allows bigger read from the driver, which reduces the number of syscall and make the system faster Signed-off-by: Federico Vaga <federico.vaga@cern.ch>
113ff999 · Federico Vaga · fe5b9727 · 113ff999
Commit 113ff999 authored Aug 10, 2018 by Federico Vaga
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Showing with 36 additions and 16 deletions

fmctdc-lib.c lib/fmctdc-lib.c +36 -16

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--- a/lib/fmctdc-lib.c
+++ b/lib/fmctdc-lib.c
@@ -640,41 +640,61 @@ int fmctdc_read(struct fmctdc_board *userb, unsigned int channel,
 		struct fmctdc_time *t, int n, int flags)
 {
 	__define_board(b, userb);
-	int i, j;
+	int i;
+	int n_ts;
 	fd_set set;
-	struct ft_hw_timestamp data;
+	struct ft_hw_timestamp *data;
 	if (channel >= FMCTDC_NUM_CHANNELS) {
 		errno = EINVAL;
 		return -1;
 	}
-	for (i = 0; i < n;) {
+	data = calloc(n, sizeof(*data));
-		j = read(b->fdd[channel], &data, sizeof(data));
+	if (!data) {
-		if (j == sizeof(data)) {
+		errno = ENOMEM;
-			fmctdc_ts_convert(&t[i], &data);
+		return -1;
-			++i;
+	}
-			continue;
+	i = 0;
+	while (i < n) {
+		n_ts = read(b->fdd[channel], &data[i], sizeof(*data) * (n - i));
+		if (n_ts < 0 && errno != EAGAIN) {
+			if (i == 0)
+				goto err;
+			else
+				goto out;
 		}
-		if (j < 0 && errno != EAGAIN)
+		if (n_ts % sizeof(*data) == 0) { /* Good samples here */
-			return -1;
+			n_ts /= sizeof(*data);
+			n_ts += i;
+			for (; i < n_ts && i < n; i++)
+				fmctdc_ts_convert(&t[i], &data[i]);
+			continue; /* the while loop */
+		}
+		if (i) /* error but before we got something */
+			goto out;
-		/* so, it's EAGAIN: if we already got something, we are done */
-		if (i)
-			return i;
 		/* EAGAIN at first sample */
-		if (j < 0 && flags == O_NONBLOCK)
+		if (n_ts < 0 && flags == O_NONBLOCK)
 			return -1;
 		/* So, first sample and blocking read. Wait.. */
 		FD_ZERO(&set);
 		FD_SET(b->fdc[channel], &set);
 		if (select(b->fdc[channel] + 1, &set, NULL, NULL, NULL) < 0)
-			return -1;
+			goto err;
-		continue;
 	}
+out:
+	free(data);
 	return i;
+err:
+	free(data);
+	return -1;
 }
 /**