don't wait before fetching first set of data

.gitignore

@@ -1 +1,2 @@
 1--transforming-sync-to-async/provided-code/target
+target

Cargo.lock

@@ -95,6 +95,24 @@ dependencies = [
  "event-listener",
 ]
 
+[[package]]
+name = "async-process"
+version = "1.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a9d28b1d97e08915212e2e45310d47854eafa69600756fc735fb788f75199c9"
+dependencies = [
+ "async-io",
+ "async-lock",
+ "autocfg",
+ "blocking",
+ "cfg-if",
+ "event-listener",
+ "futures-lite",
+ "rustix",
+ "signal-hook",
+ "windows-sys 0.48.0",
+]
+
 [[package]]
 name = "async-std"
 version = "1.12.0"
@@ -106,6 +124,7 @@ dependencies = [
  "async-global-executor",
  "async-io",
  "async-lock",
+ "async-process",
  "crossbeam-utils",
  "futures-channel",
  "futures-core",
@@ -369,19 +388,46 @@ dependencies = [
 ]
 
 [[package]]
-name = "futures-channel"
-version = "0.3.21"
+name = "futures"
+version = "0.3.30"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c3083ce4b914124575708913bca19bfe887522d6e2e6d0952943f5eac4a74010"
+checksum = "645c6916888f6cb6350d2550b80fb63e734897a8498abe35cfb732b6487804b0"
+dependencies = [
+ "futures-channel",
+ "futures-core",
+ "futures-executor",
+ "futures-io",
+ "futures-sink",
+ "futures-task",
+ "futures-util",
+]
+
+[[package]]
+name = "futures-channel"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eac8f7d7865dcb88bd4373ab671c8cf4508703796caa2b1985a9ca867b3fcb78"
 dependencies = [
  "futures-core",
+ "futures-sink",
 ]
 
 [[package]]
 name = "futures-core"
-version = "0.3.21"
+version = "0.3.30"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0c09fd04b7e4073ac7156a9539b57a484a8ea920f79c7c675d05d289ab6110d3"
+checksum = "dfc6580bb841c5a68e9ef15c77ccc837b40a7504914d52e47b8b0e9bbda25a1d"
+
+[[package]]
+name = "futures-executor"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a576fc72ae164fca6b9db127eaa9a9dda0d61316034f33a0a0d4eda41f02b01d"
+dependencies = [
+ "futures-core",
+ "futures-task",
+ "futures-util",
+]
 
 [[package]]
 name = "futures-io"
@@ -405,27 +451,44 @@ dependencies = [
 ]
 
 [[package]]
-name = "futures-sink"
-version = "0.3.21"
+name = "futures-macro"
+version = "0.3.30"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "21163e139fa306126e6eedaf49ecdb4588f939600f0b1e770f4205ee4b7fa868"
+checksum = "87750cf4b7a4c0625b1529e4c543c2182106e4dedc60a2a6455e00d212c489ac"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.52",
+]
+
+[[package]]
+name = "futures-sink"
+version = "0.3.30"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9fb8e00e87438d937621c1c6269e53f536c14d3fbd6a042bb24879e57d474fb5"
 
 [[package]]
 name = "futures-task"
-version = "0.3.21"
+version = "0.3.30"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "57c66a976bf5909d801bbef33416c41372779507e7a6b3a5e25e4749c58f776a"
+checksum = "38d84fa142264698cdce1a9f9172cf383a0c82de1bddcf3092901442c4097004"
 
 [[package]]
 name = "futures-util"
-version = "0.3.21"
+version = "0.3.30"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d8b7abd5d659d9b90c8cba917f6ec750a74e2dc23902ef9cd4cc8c8b22e6036a"
+checksum = "3d6401deb83407ab3da39eba7e33987a73c3df0c82b4bb5813ee871c19c41d48"
 dependencies = [
+ "futures-channel",
  "futures-core",
+ "futures-io",
+ "futures-macro",
+ "futures-sink",
  "futures-task",
+ "memchr",
  "pin-project-lite",
  "pin-utils",
+ "slab",
 ]
 
 [[package]]
@@ -663,6 +726,7 @@ dependencies = [
  "async-std",
  "chrono",
  "clap",
+ "futures",
  "yahoo_finance_api",
 ]
 
@@ -1087,6 +1151,25 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "signal-hook"
+version = "0.3.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8621587d4798caf8eb44879d42e56b9a93ea5dcd315a6487c357130095b62801"
+dependencies = [
+ "libc",
+ "signal-hook-registry",
+]
+
+[[package]]
+name = "signal-hook-registry"
+version = "1.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8229b473baa5980ac72ef434c4415e70c4b5e71b423043adb4ba059f89c99a1"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "slab"
 version = "0.4.6"

Cargo.toml

@@ -10,4 +10,5 @@ version = "0.1.0"
 chrono = { version = "0.4", features = ["serde"] }
 clap = {version = "3.1.8", features = ["derive"]}
 yahoo_finance_api = "1.1"
-async-std = { version = "1.6", features = ["attributes", "tokio1"] }
+async-std = { version = "1.6", features = ["attributes", "tokio1", "unstable"] }
+futures = "0.3"

src/main.rs

@@ -1,6 +1,12 @@
+use async_std::prelude::*;
 use chrono::prelude::*;
+
 use clap::Parser;
-use std::io::{Error, ErrorKind};
+use futures::future::try_join_all;
+use std::{
+    io::{Error, ErrorKind},
+    time::Duration,
+};
 use yahoo_finance_api as yahoo;
 
 #[derive(Parser, Debug)]
@@ -118,18 +124,7 @@ async fn fetch_closing_data(
     }
 }
 
-#[async_std::main]
-async fn main() -> std::io::Result<()> {
-    let opts = Opts::parse();
-    let from: DateTime<Utc> = opts.from.parse().expect("Couldn't parse 'from' date");
-    let to = Utc::now();
-
-    // a simple way to output a CSV header
-    println!("period start,symbol,price,change %,min,max,30d avg");
-    for symbol in opts.symbols.split(',') {
-        let closes = fetch_closing_data(&symbol, &from, &to).await?;
-        if !closes.is_empty() {
-            // min/max of the period. unwrap() because those are Option types
+fn output_csv_line(closes: Vec<f64>, from: DateTime<Utc>, symbol: &str) {
     let period_max: f64 = max(&closes).unwrap();
     let period_min: f64 = min(&closes).unwrap();
     let last_price = *closes.last().unwrap_or(&0.0);
@@ -147,7 +142,49 @@ async fn main() -> std::io::Result<()> {
         period_max,
         sma.last().unwrap_or(&0.0)
     );
+}
+
+async fn fetch_and_output_closing_data(
+    symbol: &str,
+    from: DateTime<Utc>,
+    to: DateTime<Utc>,
+) -> std::io::Result<()> {
+    let closes = fetch_closing_data(&symbol, &from, &to).await?;
+    if !closes.is_empty() {
+        output_csv_line(closes, from, symbol);
     }
+    Ok(())
+}
+
+async fn fetch_and_output_symbol_data(
+    symbols: &str,
+    from: DateTime<Utc>,
+    to: DateTime<Utc>,
+) -> std::io::Result<()> {
+    let mut fs = vec![];
+    for symbol in symbols.split(',') {
+        let f = fetch_and_output_closing_data(symbol, from, to);
+        fs.push(f);
+    }
+    try_join_all(fs).await?;
+    Ok(())
+}
+
+#[async_std::main]
+async fn main() -> std::io::Result<()> {
+    let opts = Opts::parse();
+    let from: DateTime<Utc> = opts.from.parse().expect("Couldn't parse 'from' date");
+    let to = Utc::now();
+
+    // a simple way to output a CSV header
+    println!("period start,symbol,price,change %,min,max,30d avg");
+
+    // initial data fetch
+    fetch_and_output_symbol_data(&opts.symbols, from, to).await?;
+
+    let mut interval = async_std::stream::interval(Duration::from_secs(30));
+    while let Some(_) = interval.next().await {
+        fetch_and_output_symbol_data(&opts.symbols, from, to).await?;
     }
     Ok(())
 }