Supplement statements with references to C11 and LLVM docs

References to C11 standard were added when explaining properties of
atomic type and operations. More information of codegen on atomic
operations is added as a footnote with a link to LLVM's document as an
example.

Author: idoleat

concurrency-primer.tex

@@ -321,8 +321,14 @@ \section{Enforcing law and order}
 This model, defined by Leslie Lamport in 1979,
 is called \introduce{sequential consistency}.
 
-Notice that using atomic variables as an lvalue expression, such as \monobox{v\_ready = true} and \monobox{while(!v\_ready)}, is a convenient alternative to explicitly using \monobox{atomic\_load} or \monobox{atomic\_store}. 
-Lvalue-to-rvalue conversion (which models a memory read from an atomic location to a CPU register) strips atomicity along with other qualifiers. 
+Notice that using atomic variables as an lvalue expression, such as \monobox{v\_ready = true} and \monobox{while(!v\_ready)}, is a convenient alternative to explicitly using \monobox{atomic\_load} or \monobox{atomic\_store}.\punckern\footnote{%
+Atomic load/store are not necessary generated as atomic instructions.
+Under a weaker consistency model, they could simply be normal load/store,
+and their code generation can vary across different architectures.
+Checkout \href{https://llvm.org/docs/Atomics.html\#atomics-and-codegen}{LLVM's document} as an example to see how it is handled.}
+As stated in C11 6.7.2.4 and 6.7.3, the properties associated with atomic types are meaningful only for expressions that are
+lvalues.
+Lvalue-to-rvalue conversion (which models a memory read from an atomic location to a CPU register) strips atomicity along with other qualifiers.
 
 \section{Atomicity}
 \label{atomicity}
@@ -465,7 +471,7 @@ \subsection{Compare and swap}
 Finally, we have \introduce{compare-and-swap} (\textsc{CAS}),
 sometimes called \introduce{compare-and-exchange}.
 It allows us to conditionally exchange a value \emph{if} its previous value matches the expected one.
-In \clang{} and \cplusplus{}, \textsc{CAS} resembles the following,
+In \clang{} and \cplusplus{}, as noted in C11 7.17.7.4, \textsc{CAS} resembles the following,
 if it were executed atomically:
 \begin{ccode}
 /* A is an atomic type. C is the non-atomic type corresponding to A */
@@ -952,7 +958,9 @@ \subsection{Relaxed}
         if (job->args == NULL) {
             atomic_store(&thrd_pool->state, idle);
         } else {
-            printf("Hello from job %d\n", *(int *)job->args);
+            void *ret_value = job->func(job->args);
+            job->future->result = ret_value;
+            atomic_flag_clear(&job->future->flag);
             free(job->args);
             free(job); // could cause dangling pointer in other threads
         }