commit 8ff1c82b5235653c8a56a44dedc494c6d8eec618
parent f8d847dcc22c0b66eb3a1fde5b0412aca4d6e123
Author: dwrz <dwrz@dwrz.net>
Date: Fri, 5 Jun 2020 16:13:03 +0000
Update concurrency slides
Diffstat:
1 file changed, 46 insertions(+), 33 deletions(-)
diff --git a/concurrency/slides.org b/concurrency/slides.org
@@ -61,7 +61,7 @@ A second is a duration, not an instant.
Two things can happen in the same second and not be simultaneous.
-In computer science, this nuance matters.
+With computers, this nuance matters.
* 9. Time
@@ -98,10 +98,12 @@ Source: [[https://www.prowesscorp.com/computer-latency-at-a-human-scale/]]
* 12. Cooking Recipes
- Step-by-step
-- Concurrent
- - Pre-heat oven
- - Boil water
- - Timers
+- Concurrent:
+ - Handle other tasks while:
+ - Preheating oven
+ - Boiling water
+ - Waiting for timers
+ - Switching back to a task when it is ready for mork work.
* 13. Multitasking
@@ -117,6 +119,10 @@ Computers can "simultaneously" work on:
Combination of:
- Operating System *Scheduler*
- Hardware (/interrupts/)
+ - Keyboard
+ - Filesystem
+ - Network Card
+ - Timer
* 17. Cooperative Scheduling
[[file:images/cooperative-scheduling.jpg]]
@@ -149,6 +155,7 @@ A little more nuance.
- Different /parts/ of a recipe
- Process :: a program in execution.
+ - Unique resources (memory, code, files, etc.).
- Start off with one thread.
- Can /fork/.
- Communicate via inter-process communication (IPC).
@@ -188,32 +195,46 @@ int main() {
Source: [[https://medium.com/preezma/node-js-event-loop-architecture-go-deeper-node-core-c96b4cec7aa4]]
-* 27. Go
-Runtime multi-threading, multiplexes goroutines onto threads.
+* 27. Aside: Event Loop
+What is the output of the following? Why?
+#+begin_src javascript
+console.log('start');
+
+setTimeout(() => console.log('1'), 0);
+
+console.log('middle');
+
+setTimeout(() => console.log('2'), 0);
+
+console.log('end');
+#+end_src
+
+* 28. Go
+*Runtime scheduler* manages multiple threads.
[[file:images/go-scheduler.png]]
Source: https://freethreads.net/2019/01/23/go-runtime-scheduler-design-internals/
-* 28. Quick Review
+* 29. Quick Review
- Sequential versus Concurrent Steps
- Compare with recipes.
- Concurrency versus Parallelism
- Parallelism: multiple cooks, simultaneously /doing/.
- - Concurrency: one or more cooks, simultaneously /dealing/ with many tasks.
+ - Concurrency: one or more cooks, /dealing/ with many tasks.
- Operating System Scheduler
- Processes and Threads
- Languages and Runtimes
-* 29. Part 2: Using Concurrency
+* 30. Part 2: Using Concurrency
Typical use cases:
-- Network I/O
- - Requests between clients and servers.
- - Requests to a database.
- - Requests between microservices.
- - Requests to external APIs.
+- Network I/O between:
+ - Clients and servers.
+ - Services and database(s).
+ - Microservices.
+ - Service and external APIs.
- User interfaces
- Capturing user input
@@ -223,25 +244,11 @@ Typical use cases:
- Solving problems that are best expressed with concurrency.
-* 30. JavaScript
-
-What is the output of the following? Why?
-#+begin_src javascript
-console.log('start');
-
-setTimeout(() => console.log('1'), 0);
-
-console.log('middle');
-
-setTimeout(() => console.log('2'), 0);
-
-console.log('end');
-#+end_src
-
* 31. Go Examples
1. Shared Memory with Mutex (Mutual Exclusion)
- Pitfall: synchronization, debugging.
+
2. Message Passing (Channels and Goroutines)
- Pitfall: resources usage, complexity.
@@ -253,7 +260,6 @@ Code:
Run: [[file:cmd/mutex/run.sh]]
- Without mutex.
- - With mutex.
* 33. Data Races
[[file:images/data-race.jpg]]
@@ -265,8 +271,15 @@ Run: [[file:cmd/mutex/run.sh]]
- Purpose: protect a critical section of code.
- Effect: serialization.
+Run: [[file:cmd/mutex/run.sh]]
+ - With mutex.
+
* 35. Race Detector
+How can we be sure?
+
+Race detector can give us /some/ confidence (but no guarantees).
+
- Without mutex.
- With mutex.
@@ -286,7 +299,7 @@ Don't communicate by sharing memory, share memory by communicating.
Channels orchestrate, mutexes serialize.
#+end_quote
-* 38. Requirements
+* 38. Program Requirements
- Read CSV of zip codes
- 50 in our example
@@ -383,7 +396,7 @@ Concurrent applications running concurrently on distributed computers.
- What concurrency is
- Sequential versus concurrent
- - Comparison with recipes
+ - Comparison with recipes and cooks
- Compared to parallelism
- How it is implemented
- Operating System Scheduler and Interrupts
