init

.gitignore

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+/target

Cargo.lock

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Cargo.toml

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+[package]
+name = "rust-async"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[[bin]]
+name = "blocking"
+path = "./src/blocking.rs"
+
+[[bin]]
+name = "async-tokio"
+path = "./src/async-tokio.rs"
+
+[dependencies]
+# feature flags are documented in tokio's documentation https://docs.rs/tokio/latest/tokio/#feature-flags
+tokio = { version = "1", features = ["rt-multi-thread", "fs", "macros", "time"] }

Makefile

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+default: help
+
+async: ## Runs non-blocking program
+	cargo run --bin=async-tokio
+
+blocking: ## Runs blocking program
+	cargo run --bin=blocking
+
+help: ## Prints help for targets with comments
+	@cat $(MAKEFILE_LIST) | grep -E '^[a-zA-Z_-]+:.*?## .*$$' | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'

README.md

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+# Blocking vs Non-blocking file I/O
+
+Blocking code is available in [blockin.rs](./src/blocking.rs] and
+non-blocking in [async-tokio.rs](./src/async-tokio.rs). 
+
+Both programs read their respective source files and print it to
+stdout.
+
+## Usage
+A simple Makefile is provided for convenience:
+
+```bash
+➜  rust-async git:(master) ✗ make help
+async                          Runs non-blocking program
+blocking                       Runs blocking program
+help                           Prints help for targets with comments
+```

src/async-tokio.rs

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+use std::time::Duration;
+
+use tokio::fs;
+use tokio::time;
+
+async fn print_100() -> usize { // return type is to demonstrate syntax sugar that is available through "async" prefix
+    // actual return type is more complicated.
+    let mut count = 0;
+    while count < 10 {
+        println!("---------------SPAWNED FUTURE OUTPUT: {count}!!!!!--------");
+        time::sleep(Duration::from_nanos(1)).await;
+        count += 1;
+    }
+    count
+}
+
+#[tokio::main] // this macro expands into code that creates a runtime for executing futures 
+// when awaited, the future is sent to the runtime created by it.
+// I'm using a multi-threaded runtime(tokio feature flag "rt-multi-thread"), which creates schedules
+// = number of CPUs available by default
+async fn main() {
+    // working directory that is supplied by cargo is crate/program root
+
+    let future = fs::read_to_string("./src/async-tokio.rs");
+
+    // spawning a future is the same as backgrounding it
+    let spawn_handle = tokio::spawn(print_100());
+
+    let contents = future.await.unwrap();
+    // Rust futures are lazily evaluated, they have to be "awaited" for execution.
+    // When awaited, this line of execution is blocked until the future runs to completion
+    // rustc will complain about dead code if the following line is commented out:
+    println!("{contents}");
+
+    spawn_handle.await.unwrap(); // waiting for the spawned future to run to completion
+}

src/blocking.rs

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+use std::fs;
+fn main() {
+    // working directory that is supplied by cargo is crate/program root
+    let contents = fs::read_to_string("./src/blocking.rs").unwrap();
+    println!("{contents}");
+}