From d755c0c1f853362976c3064139646a7f621276ec Mon Sep 17 00:00:00 2001
From: ddidderr <ddidderr@paul.network>
Date: Thu, 10 Mar 2022 16:32:43 +0100
Subject: [PATCH] RwLock: 16 reader threads and 1 writer thread

Just explored a bit the locking mechanism of std::sync::RwLock.
---
 .gitignore  |  1 +
 Cargo.lock  | 14 ++++++++++
 Cargo.toml  |  9 +++++++
 src/main.rs | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 97 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100644 src/main.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..ea8c4bf
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..5fdf230
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,14 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "pfs-time-measure"
+version = "0.1.0"
+
+[[package]]
+name = "rwlocktest"
+version = "0.1.0"
+dependencies = [
+ "pfs-time-measure",
+]
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..2464621
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "rwlocktest"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+pfs-time-measure = { path = "../pfs-time-measure" }
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..bf864a7
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,73 @@
+use std::sync::{Arc,RwLock};
+use std::time::Duration;
+
+use pfs_time_measure::Clock;
+
+const NUM_THREADS:usize = 16;
+
+
+fn sleep_millis(millis: u64) {
+    std::thread::sleep(Duration::from_millis(millis));
+}
+
+fn main() {
+
+    let rwlocked = Arc::new(RwLock::new(42));
+
+    let mut threads = Vec::with_capacity(NUM_THREADS);
+
+    for x in 0..NUM_THREADS {
+
+        let r = rwlocked.clone();
+
+        let t = std::thread::spawn(move|| {
+            let mut clock = Clock::new(format!("t{x} reader_lock"), false);
+            loop {
+                {
+                    clock.restart();
+                    let rr = r.read().unwrap();
+                    clock.stop();
+                    clock.print_all_measurements();
+                    println!("[READER] acquired lock");
+                    println!("[READER] t{x}: {}!", rr);
+                    sleep_millis(500);
+                    println!("[READER] released lock");
+                }
+                sleep_millis(100);
+            }
+        });
+        threads.push(t);
+    }
+
+    let r = rwlocked.clone();
+    let twrite = std::thread::spawn(move|| {
+        sleep_millis(100);
+        let mut clock = Clock::new("writer_lock".to_string(), false);
+        loop {
+            println!("[WRITER] trying to acquire lock");
+            clock.restart();
+            match r.write() {
+                Ok(mut val) => {
+                    clock.stop();
+                    clock.print_all_measurements();
+                    println!("[WRITER] acquired lock");
+                    *val = 11;
+                    sleep_millis(600);
+                },
+                Err(e) => {
+                    clock.stop();
+                    clock.print_all_measurements();
+                    println!("[WRITER] error: {:?}", e);
+                },
+            }
+            println!("[WRITER] released lock");
+            sleep_millis(100);
+        }
+    });
+
+    for t in threads {
+        let _ = t.join();
+    }
+
+    let _ = twrite.join();
+}