[IO] make the lock implementation protecting a IoContext's cq configurable 

This change introduces a new synchronization primitive "PseudoCountingTryLock" which takes an actual lock as template and provides a CountingTryLock interface. By using a PseudoCountingTryLock we don't have to change any synchronization code in IoContext::reapCompletion.

Since all PseudoCountingTryLock code is defined in a header the compiler should see our constant return values and hopefully optimize away any check depending on those constant return values.

Options:

• spin_lock - naive CAS spin lock
• mutex - std::mutex
• counting_try_lock (default) - our own lightweight special purpose synchronization primitive

Closes !123 (closed).

emper/io/IoContext.hpp

@@ -18,10 +18,28 @@
 #include "emper-config.h"					// for EMPER_IO_WORKER_URING_ENTRIES
 #include "io/Stats.hpp"						// for Stats
 #include "lib/adt/LockedSet.hpp"	// for LockedSet
-#include "lib/sync/CountingTryLock.hpp"
 
 class Fiber;
 
+#ifdef EMPER_IO_CQ_LOCK_COUNTING_TRY_LOCK
+#include "lib/sync/CountingTryLock.hpp"
+using CqLock = emper::lib::sync::CountingTryLock;
+
+#elif defined EMPER_IO_CQ_LOCK_MUTEX
+#include <mutex>
+
+#include "lib/sync/PseudoCountingTryLock.hpp"
+using CqLock = emper::lib::sync::PseudoCountingTryLock<std::mutex>;
+
+#elif defined EMPER_IO_CQ_LOCK_SPIN_LOCK
+#include "lib/sync/PseudoCountingTryLock.hpp"
+#include "lib/sync/SpinLock.hpp"
+using CqLock = emper::lib::sync::PseudoCountingTryLock<emper::lib::sync::SpinLock>;
+
+#else
+#error Uknown cq lock implementation
+#endif
+
 namespace emper::io {
 class Future;
 
@@ -40,7 +58,7 @@ class IoContext : public Logger<LogSubsystem::IO> {
 
 	static thread_local IoContext *workerIo;
 	// TryLock protecting the completion queue of ring.
-	ALIGN_TO_CACHE_LINE lib::sync::CountingTryLock cq_lock;
+	ALIGN_TO_CACHE_LINE CqLock cq_lock;
 	struct io_uring ring;
 
 	// In a worker's IoContext This eventfd is registered with the io_uring to get completion