[libcamera-devel] [PATCH 2/2] libcamera: base: signal: Prevent excessive slot usage

[Kieran Bingham]

Slots are not expected to be connected to lots of signals. Our normal
use case is a one to one mapping with a signal expected to call one
slot.

While we support multiple slots, excessive use is likely the result of a
bug indicating a failure to disconnect slots or repeated connection of a
slot which can lead to memory leaks and poor performance when deleting
the Object.

Assert that a maximum of 8 slots are connected which will catch any bug
and still allow some multiple slot usage. If this limit is ever met it
can be extended and considered at that time.

Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---

Note that this patch causes the CTS tests to fail as they hit this
assertion.

It is not yet investigated if we really need more slots or if the
assertion has already caught a slot-leak, but posting for early review
anyway.

 src/libcamera/base/signal.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/libcamera/base/signal.cpp b/src/libcamera/base/signal.cpp
index 9df45d079a42..7e6a23cc909d 100644
--- a/src/libcamera/base/signal.cpp
+++ b/src/libcamera/base/signal.cpp
@@ -7,6 +7,7 @@
 
 #include <libcamera/base/signal.h>
 
+#include <libcamera/base/log.h>
 #include <libcamera/base/mutex.h>
 
 /**
@@ -35,6 +36,13 @@ void SignalBase::connect(BoundMethodBase *slot)
 	if (object)
 		object->connect(this);
 	slots_.push_back(slot);
+
+	/*
+	 * Slots are not expected to be used to connect many items. If we exceed
+	 * a reasonable amount, presume that there is a bug and fail fast on
+	 * debug builds.
+	 */
+	ASSERT(slots_.size() < 8);
 }
 
 void SignalBase::disconnect(Object *object)
-- 
2.32.0