add sync_cow and arc_swap

Author: smallnest

special/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+arc-swap = "1.6.0"
 async-lock = "2.5.0"
 async-oneshot = "0.5.0"
 async-weighted-semaphore = "0.2.1"
@@ -17,6 +18,7 @@ awaitgroup = "0.6.0"
 barrage = "0.2.3"
 catty = "0.1.5"
 concurrent-queue = "1.2.4"
+crossbeam-utils = "0.8.14"
 dashmap = "5.4.0"
 event-listener = "2.5.3"
 evmap = "10.0.2"
@@ -31,6 +33,7 @@ simple-mutex = "1.1.5"
 singleflight-async = "0.1.1"
 slab = "0.4.7"
 smol = "1.2.5"
+sync_cow = "0.1.1"
 tokio = { version = "1.21.2", features = ["full"] }
 triggered = "0.1.2"
 triple_buffer = "6.2.0"

special/src/arcswap.rs

@@ -0,0 +1,24 @@
+
+use arc_swap::ArcSwap;
+use std::sync::Arc;
+use crossbeam_utils::thread;
+
+pub fn arc_swap_example() {
+    let value = ArcSwap::from(Arc::new(5));
+    thread::scope(|scope| {
+        scope.spawn(|_| {
+            let new_value = Arc::new(4);
+            value.store(new_value);
+        });
+        for _ in 0..10 {
+            scope.spawn(|_| {
+                loop {
+                    let v = value.load();
+                    println!("value is {}", v);
+                    return;
+                }
+            }); 
+        }   
+    }).unwrap()
+    
+}

special/src/lib.rs

@@ -7,6 +7,8 @@ mod queue;
 mod scc_examples;
 mod sema_examples;
 mod singleflight_example;
+mod synccow;
+mod arcswap;
 
 pub use oslock::*;
 pub use oneshots::*;
@@ -16,4 +18,6 @@ pub use notify::*;
 pub use queue::*;
 pub use scc_examples::*;
 pub use sema_examples::*;
-pub use singleflight_example::*;
+pub use singleflight_example::*;
+pub use synccow::*;
+pub use arcswap::*;

special/src/main.rs

@@ -58,6 +58,9 @@ fn main() {
     singleflight_example();
     async_singleflight_example();
 
+    sync_cow_example().unwrap();
+    arc_swap_example();
+
 }
 
 

special/src/singleflight_example.rs

@@ -1,7 +1,6 @@
 use futures::future::join_all;
 use singleflight_async::SingleFlight;
 use std::sync::Arc;
-use std::time::Duration;
 
 use async_singleflight::Group;
 

special/src/synccow.rs

@@ -0,0 +1,36 @@
+use sync_cow::SyncCow;
+use std::sync::Arc;
+use std::any::Any;
+
+
+pub fn sync_cow_example() -> Result<(),Box<dyn Any + Send>> {
+    let cow = Arc::new(SyncCow::new(5));
+
+    // Arc is only needed to pass the ref to the threads
+    let cow_write_arc = cow.clone();
+    let cow_read_arc = cow.clone();
+    let cow_result_arc = cow.clone();
+
+    let writer = std::thread::spawn(move || {
+        let cow = &*cow_write_arc; // unpack immediately to avoid Arc deref
+        let mut val = 0;
+        cow.edit(|x| {
+            val = *x;
+            *x = 4;
+        });
+        println!("Cow was {} when writing", val);
+    });
+
+    let reader = std::thread::spawn(move || {
+        let cow = &*cow_read_arc; // unpack immediately to avoid Arc deref
+        println!("Cow was {} when reading", cow.read());
+    });
+
+    writer.join()?;
+    reader.join()?;
+
+    let cow = &*cow_result_arc; // unpack immediately to avoid Arc deref
+    println!("Cow was {} when result", cow.read());
+
+    Ok(())
+}