libcamera: ProcessManager: make ProcessManager lifetime explicitly managed

If any Process instances are destroyed after the ProcessManager is
destroyed, then a segfault will occur.

Fix this by making the lifetime of the ProcessManager explicit, and make
the CameraManager construct and deconstruct (automatically, via a member
variable) the ProcessManager.

Update the tests accordingly.

Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Jacopo Mondi <jacopo@jmondi.org>

include/libcamera/internal/process.h

@@ -7,6 +7,7 @@
 #ifndef __LIBCAMERA_INTERNAL_PROCESS_H__
 #define __LIBCAMERA_INTERNAL_PROCESS_H__
 
+#include <signal.h>
 #include <string>
 #include <vector>
 
@@ -14,6 +15,8 @@
 
 namespace libcamera {
 
+class EventNotifier;
+
 class Process final
 {
 public:
@@ -50,6 +53,32 @@ private:
 	friend class ProcessManager;
 };
 
+class ProcessManager
+{
+public:
+	ProcessManager();
+	~ProcessManager();
+
+	void registerProcess(Process *proc);
+
+	static ProcessManager *instance();
+
+	int writePipe() const;
+
+	const struct sigaction &oldsa() const;
+
+private:
+	static ProcessManager *self_;
+
+	void sighandler(EventNotifier *notifier);
+
+	std::list<Process *> processes_;
+
+	struct sigaction oldsa_;
+	EventNotifier *sigEvent_;
+	int pipe_[2];
+};
+
 } /* namespace libcamera */
 
 #endif /* __LIBCAMERA_INTERNAL_PROCESS_H__ */