Vault sync: 2022-01-26 22:14:35

School/Analyse/Periode 2/Week 1.md

@@ -89,7 +89,29 @@ Execution of concurrent program proceeds by executing a sequence of the statemen
 p1->q2->p2->q1 is not possible. because we are breaking the order of execution of program q.  q must execute q1 before q2.
 
 # Atomic statement
-
+Atomic statement model assumes that a statement is executed to completion without the possibility of interleaving statements from other process.
+
+Main property of atomic statement is: they cant be divided.
+
+A single machine level instruction is always atomic.
+
+
+# Tracing & testing
+
+concurrent programs are hard to develop and test.
+
+Concurrency bugs:
+
+- Simultaneous access same db record
+- Atomicity violatitions
+- Deadlocks
+
+These bugs are hard to detect and fix.
+
+# Correctness
+Sequetial programs wil always give the same result. Debugging makes sense.
+
+Concurrent programs do not behave like this. Some instances may give correct output and some not.