Add "Memory consistency models" subsection to "Memory orderings" section by yutingshih · Pull Request #16 · sysprog21/concurrency-primer

yutingshih · 2024-06-28T20:55:39Z

This pull request aims to enhance the comprehensiveness of the “Memory orderings” section of this book. Currently, the section primarily covers memory orders defined in C11/C++11 but lacks discussion on hardware assumptions regarding memory consistency. Thus I made the following changes:

Reorganization
- Moved the content originally under “Memory orderings” related to C11/C++11 atomics to a dedicated subsection titled “C11/C++ atomics” within the “Memory orderings” section.
Addition
- Introduced a new subsection titled “Memory consistency models”
  - Detailed descriptions of sequential consistency, x86 total store order, and ARM’s relaxed memory order.
  - Included schematic diagrams illustrating hardware architectures and litmus tests to aid readers’ comprehension.

concurrency-primer.tex

jserv · 2024-07-06T08:11:34Z

concurrency-primer.tex

+\subsection{Memory consistency models}
+
+When a program is compiled and executed, it doesn't always follow the written order.
+The system may change the sequence and optimize it to simulate line-by-line execution, as long as the final result matches the expected outcome.


You should address the impact from modern microprocessors and optimizing compilers.

jserv · 2024-07-06T08:11:59Z

concurrency-primer.tex

+When a program is compiled and executed, it doesn't always follow the written order.
+The system may change the sequence and optimize it to simulate line-by-line execution, as long as the final result matches the expected outcome.
+
+This requires an agreement between the programmer and the system (hardware, compiler, etc.), ensuring that if the rules are followed, the execution will be correct.


Merge the statement into the previous paragraph.

jserv

Rebase the latest main branch.

jserv

Instead of git merge, do git rebase.

1. split setences into separate lines 2. change the quotation marks "..." as ``...''

- Changed "doesn't" to "does not" for formal English writing - Fixed the inconsistency of quotation marks - Merged related statements into one paragraph

jserv · 2024-07-23T07:59:40Z

concurrency-primer.tex

+
+The write order seen by one thread can differ from the order seen by other threads because write operations can be reordered during propagation.
+However, reads and writes to the same memory address must still follow a total order.
+Therefore, the following litmus test cannot result in \monobox{r1 = 1}, \monobox{r2 = 2}, but \monobox{r3 = 2}, \monobox{r4 = 1}.


Provide some information about running Litmus tests.

jserv · 2024-07-23T11:42:07Z

concurrency-primer.tex

+
+\subsubsection{Sequential consistency (SC)}
+
+In the 1970s, Leslie Lamport proposed the most common memory consistency model, sequential consistency (SC), defined as follows:


Add some references at the end of this document.

jserv reviewed Jun 29, 2024

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