New post: umich/w25_491_journal

3 files changed, 56 insertions, 1 deletions

diff --git a/docs/umich/index.md b/docs/umich/index.md
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--- a/docs/umich/index.md
+++ b/docs/umich/index.md
@@ -18,3 +18,4 @@ so basically i live in ann arbor now
     - [GERMAN 231: Second-Year German](f24_deutsch.md)
 - [Winter 2025 Journal](w25_journal.md)
     - [EECS 461: Embedded Control Systems](w25_461_journal.md)
+    - [EECS 491: Distributed Systems](w25_491_journal.md)
diff --git a/docs/umich/w25_491_journal.md b/docs/umich/w25_491_journal.md
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+# Winter 2025 Course Journal: EECS 491
+
+Course Title: Distributed Systems
+
+## Motivation
+
+This is one of the only three upper-level courses that doesn't conflict
+with my schedule. Also, Brian Noble is one of my favorite professors.
+
+When he was teaching 482, Brian brings up 491 sometimes, and if he teaches
+it, it has to be good. Although I'm not a software person, it might come
+useful in designing a mesh of embedded systems.
+
+## Go language
+
+I wrote a little bit of Go in high school but it was nothing serious.
+
+Brian said we use Go because it was invented at Google to power their
+distributed systems, concurrency and all that stuff. He also emphasized we
+were to write "idiomatic Go", which means making use of strengths in the
+language.
+
+Being C-like makes it easy to pick up, but there's new stuff. So far, my
+favorite thing is the `for ... select` loop and it's incredibly cool.
+
+Over the winter I've been doing an embedded project in C++ with FreeRTOS.
+In FreeRTOS, one way to block a task until data shows up is to receive
+from a queue. The problem is, I need to wait for three events (represented
+as three structs), but you can only shove one type in a queue. So what
+I ended up doing is write a wrapper struct with an event type and
+a pointer, which I then cast to various types based on event type.
+
+With Go, each queue would be a channel, and you could wait for three all
+at once.
+
+The `go` keyword in go spawns a goroutine, which is basically like
+spawning a thread, but safer and cheaper.
+
+Another big thing that's different from the C world, namely 482, is that
+we're forbidden from using mutexes or any low-level synchronization
+mechanism. We're also cautioned against passing values by pointer to two
+concurrent processes. Copying a couple kilobytes is negligible compared to
+network roundtrips.
+
+## Non-deterministic behavior
+
+I've taken 482, so I'm familiar with programs where things happen in
+a different order each time. And I know that, if there is more than one
+thing in a pool, you cannot predict which one is getting out first. This
+can lead to non-deterministic behavior, and that's ok as long as it's in
+the set of "allowed" non-deterministic behaviors. This reminds me of a Tom
+Scott video that explains why computers "can't count", e.g. why the number
+of upvotes on a Reddit post changes every time you refresh.
diff --git a/docs/umich/w25_journal.md b/docs/umich/w25_journal.md
index ed1bb83..90b8c0e 100644
--- a/docs/umich/w25_journal.md
+++ b/docs/umich/w25_journal.md
@@ -23,7 +23,8 @@ Those I enrolled in initially:
 - [EECS 461: Embedded Control Systems](w25_461_journal.md)
 - EECS 330: Antennas and Wireless
 - EECS 201: Enrolled because I needed exactly one credit
-- EECS 491: Distributed Systems. Not sure to drop or not.
+- [EECS 491: Distributed Systems](w25_491_journal.md). <s>Not sure to drop
+  or not.</s> Eventually did not drop.
 - EECS 493: UI Development. Dropped because (1) I'm not doing web dev for
   a living and (2) it involves "AI prototyping".