Planner: don't return static data in fake_dc()

fake_dc() used to return a statically allocated dc with statically
allocated samples. This is of course a questionable practice in
the light of multi-threading / resource ownership. Once these
problems were recognized, the parameter "alloc" was added. If set
to true, the function would still return a statically allocated
dc, but heap-allocated samples, which could then be copied in
a different dc.

All in all an ownership nightmare and a recipie for disaster.
The returned static dc was only used as a pointer to the samples
anyway. There are four callers of fake_dc() and they all have access
to a dc-structure without samples. Therefore, change the semantics
of fake_dc() to fill out the passed in dc. If the caller does
not care about the samples, it can simply reset the sample number
to zero after work.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

1 files changed, 16 insertions, 12 deletions

diff --git a/core/dive.c b/core/dive.c
index 811c0270c..3d7c0f486 100644
--- a/core/dive.c
+++ b/core/dive.c
@@ -714,22 +714,26 @@ void copy_samples(struct divecomputer *s, struct divecomputer *d)
 		memcpy(d->sample, s->sample, nr * sizeof(struct sample));
 }
 
+/* make room for num samples; if not enough space is available, the sample
+ * array is reallocated and the existing samples are copied. */
+void alloc_samples(struct divecomputer *dc, int num)
+{
+	if (num > dc->alloc_samples) {
+		dc->alloc_samples = (dc->alloc_samples * 3) / 2 + 10;
+		dc->sample = realloc(dc->sample, dc->alloc_samples * sizeof(struct sample));
+		if (!dc->sample)
+			dc->samples = dc->alloc_samples = 0;
+	}
+}
+
 struct sample *prepare_sample(struct divecomputer *dc)
 {
 	if (dc) {
 		int nr = dc->samples;
-		int alloc_samples = dc->alloc_samples;
 		struct sample *sample;
-		if (nr >= alloc_samples) {
-			struct sample *newsamples;
-
-			alloc_samples = (alloc_samples * 3) / 2 + 10;
-			newsamples = realloc(dc->sample, alloc_samples * sizeof(struct sample));
-			if (!newsamples)
-				return NULL;
-			dc->alloc_samples = alloc_samples;
-			dc->sample = newsamples;
-		}
+		alloc_samples(dc, nr + 1);
+		if (!dc->sample)
+			return NULL;
 		sample = dc->sample + nr;
 		memset(sample, 0, sizeof(*sample));
 
@@ -922,7 +926,7 @@ void per_cylinder_mean_depth(struct dive *dive, struct divecomputer *dc, int *me
 		return;
 	}
 	if (!dc->samples)
-		dc = fake_dc(dc, false);
+		fake_dc(dc);
 	struct event *ev = get_next_event(dc->events, "gaschange");
 	for (i = 0; i < dc->samples; i++) {
 		struct sample *sample = dc->sample + i;