Fix 2 uninitialized variables (#147)

* Code rewrite of swdsm_argo_barrier() to avoid unitialized variable

New(er) compiler versions report that variable `barrierlockholder` may
be used unitialized in this function.  This was known for a while now,
but our (local) fix was unsatisfactory and was therefore not pushed to
the code base.  Motivated by #146, which is also not perfect as a fix,
we have decided to rewrite that code and eliminate the uses of this
variable, paying some cost in (small) code duplication.

Closes #146

Co-authored by: @davidklaftenegger

* Initialize variable to suppress warning

Author: kostis

src/backend/mpi/swdsm.cpp

@@ -1023,7 +1023,6 @@ void self_upgrade(argo::backend::upgrade_type upgrade) {
 }
 
 void swdsm_argo_barrier(int n, argo::backend::upgrade_type upgrade) {
-	pthread_t barrierlockholder;
 	double t1 = MPI_Wtime();
 
 	// Wait for n threads to arrive
@@ -1038,7 +1037,6 @@ void swdsm_argo_barrier(int n, argo::backend::upgrade_type upgrade) {
 
 	// Let one thread per node perform MPI operations
 	if(pthread_mutex_trylock(&barriermutex) == 0) {
-		barrierlockholder = pthread_self();
 		std::unique_lock lock(sync_lock);
 
 		// Perform SD followed by SI
@@ -1051,14 +1049,14 @@ void swdsm_argo_barrier(int n, argo::backend::upgrade_type upgrade) {
 			self_upgrade(upgrade);
 			MPI_Barrier(argo_comm);
 		}
-	}
-
-	// Wait for n threads to arrive
-	pthread_barrier_wait(&threadbarrier[n]);
-	if (pthread_equal(barrierlockholder, pthread_self())) {
+		// Wait for n threads to arrive
+		pthread_barrier_wait(&threadbarrier[n]);
 		pthread_mutex_unlock(&barriermutex);
 		stats.barriers++;
 		stats.barriertime += MPI_Wtime() - t1;
+	} else {
+		// For everybody else wait for n threads to arrive
+		pthread_barrier_wait(&threadbarrier[n]);
 	}
 }
 

tests/lock.cpp

@@ -31,7 +31,7 @@ constexpr std::size_t cache_size = size;
 
 /** @brief number of threads to spawn for some of the tests */
 constexpr int nThreads = 16;
-/** @brief number of itereations to run for some of the tests */
+/** @brief number of iterations to run for some of the tests */
 constexpr int iter = 10000;
 
 /**
@@ -74,7 +74,7 @@ class LockTest : public testing::Test {
  */
 TEST_F(LockTest, TAS_trylock_all) {
 	bool *did_increment;
-	bool res;
+	bool res = false;
 	counter = argo::conew_<int>();
 	did_increment = argo::conew_array<bool>(argo::number_of_nodes());