TankBar: don't risk dereferencing stale pointers

Basically we could end up in a situation where the plotInfo is no longer
valid, yet the model changes and triggers a redraw before the new data is
passed into the TankBar.

Instead of chasing that race condition it seemed much easier to just copy
the plot_data entries and the gas information in the dive.

Fixes #716

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

2 files changed, 20 insertions, 12 deletions

diff --git a/qt-ui/profile/tankitem.cpp b/qt-ui/profile/tankitem.cpp
index a5ec5050c..42692aacd 100644
--- a/qt-ui/profile/tankitem.cpp
+++ b/qt-ui/profile/tankitem.cpp
@@ -9,8 +9,8 @@
 TankItem::TankItem(QObject *parent) :
 	QGraphicsRectItem(),
 	dataModel(0),
-	dive(0),
-	pInfo(0)
+	pInfoEntry(0),
+	pInfoNr(0)
 {
 	height = 3;
 	QColor red(PERSIANRED1);
@@ -30,12 +30,19 @@ TankItem::TankItem(QObject *parent) :
 	trimixGradient.setColorAt(1.0, red);
 	trimix = trimixGradient;
 	air = blue;
+	memset(&diveCylinderStore, 0, sizeof(diveCylinderStore));
 }
 
 void TankItem::setData(DivePlotDataModel *model, struct plot_info *plotInfo, struct dive *d)
 {
-	pInfo = plotInfo;
-	dive = d;
+	free(pInfoEntry);
+	// the plotInfo and dive structures passed in could become invalid before we stop using them,
+	// so copy the data that we need
+	int size = plotInfo->nr * sizeof(plotInfo->entry[0]);
+	pInfoEntry = (struct plot_data *)malloc(size);
+	pInfoNr = plotInfo->nr;
+	memcpy(pInfoEntry, plotInfo->entry, size);
+	copy_cylinders(d, &diveCylinderStore, false);
 	dataModel = model;
 	connect(dataModel, SIGNAL(dataChanged(QModelIndex, QModelIndex)), this, SLOT(modelDataChanged(QModelIndex, QModelIndex)));
 	modelDataChanged();
@@ -65,7 +72,7 @@ void TankItem::modelDataChanged(const QModelIndex &topLeft, const QModelIndex &b
 {
 	// We don't have enougth data to calculate things, quit.
 
-	if (!dive || !dataModel || !pInfo || !pInfo->nr)
+	if (!dataModel || !pInfoEntry || !pInfoNr)
 		return;
 
 	// remove the old rectangles
@@ -75,21 +82,21 @@ void TankItem::modelDataChanged(const QModelIndex &topLeft, const QModelIndex &b
 	rects.clear();
 
 	// walk the list and figure out which tanks go where
-	struct plot_data *entry = pInfo->entry;
+	struct plot_data *entry = pInfoEntry;
 	int cylIdx = entry->cylinderindex;
 	int i = -1;
 	int startTime = 0;
-	struct gasmix *gas = &dive->cylinder[cylIdx].gasmix;
+	struct gasmix *gas = &diveCylinderStore.cylinder[cylIdx].gasmix;
 	qreal width, left;
-	while (++i < pInfo->nr) {
-		entry = &pInfo->entry[i];
+	while (++i < pInfoNr) {
+		entry = &pInfoEntry[i];
 		if (entry->cylinderindex == cylIdx)
 			continue;
 		width = hAxis->posAtValue(entry->sec) - hAxis->posAtValue(startTime);
 		left = hAxis->posAtValue(startTime);
 		createBar(left, width, gas);
 		cylIdx = entry->cylinderindex;
-		gas = &dive->cylinder[cylIdx].gasmix;
+		gas = &diveCylinderStore.cylinder[cylIdx].gasmix;
 		startTime = entry->sec;
 	}
 	width = hAxis->posAtValue(entry->sec) - hAxis->posAtValue(startTime);
diff --git a/qt-ui/profile/tankitem.h b/qt-ui/profile/tankitem.h
index 615a7017d..f8d4ac9f8 100644
--- a/qt-ui/profile/tankitem.h
+++ b/qt-ui/profile/tankitem.h
@@ -28,8 +28,9 @@ private:
 	DivePlotDataModel *dataModel;
 	DiveCartesianAxis *hAxis;
 	int hDataColumn;
-	struct dive *dive;
-	struct plot_info *pInfo;
+	struct dive diveCylinderStore;
+	struct plot_data *pInfoEntry;
+	int pInfoNr;
 	qreal yPos, height;
 	QBrush air, nitrox, trimix;
 	QList<QGraphicsRectItem *> rects;