#[main]
Expand description
Marks async function to be executed by the selected runtime. This macro
helps set up a Runtime
without requiring the user to use
Runtime or
Builder directly.
Note: This macro is designed to be simplistic and targets applications that do not require a complex setup. If the provided functionality is not sufficient, you may be interested in using Builder, which provides a more powerful interface.
Note: This macro can be used on any function and not just the main
function. Using it on a non-main function makes the function behave as if it
was synchronous by starting a new runtime each time it is called. If the
function is called often, it is preferable to create the runtime using the
runtime builder so the runtime can be reused across calls.
Multi-threaded runtime
To use the multi-threaded runtime, the macro can be configured using
#[tokio::main(flavor = "multi_thread", worker_threads = 10)]
The worker_threads
option configures the number of worker threads, and
defaults to the number of cpus on the system. This is the default flavor.
Note: The multi-threaded runtime requires the rt-multi-thread
feature
flag.
Current thread runtime
To use the single-threaded runtime known as the current_thread
runtime,
the macro can be configured using
#[tokio::main(flavor = "current_thread")]
Function arguments:
Arguments are allowed for any functions aside from main
which is special
Usage
Using the multi-thread runtime
#[tokio::main]
async fn main() {
println!("Hello world");
}
Equivalent code not using #[tokio::main]
fn main() {
tokio::runtime::Builder::new_multi_thread()
.enable_all()
.build()
.unwrap()
.block_on(async {
println!("Hello world");
})
}
Using current thread runtime
The basic scheduler is single-threaded.
#[tokio::main(flavor = "current_thread")]
async fn main() {
println!("Hello world");
}
Equivalent code not using #[tokio::main]
fn main() {
tokio::runtime::Builder::new_current_thread()
.enable_all()
.build()
.unwrap()
.block_on(async {
println!("Hello world");
})
}
Set number of worker threads
#[tokio::main(worker_threads = 2)]
async fn main() {
println!("Hello world");
}
Equivalent code not using #[tokio::main]
fn main() {
tokio::runtime::Builder::new_multi_thread()
.worker_threads(2)
.enable_all()
.build()
.unwrap()
.block_on(async {
println!("Hello world");
})
}
Configure the runtime to start with time paused
#[tokio::main(flavor = "current_thread", start_paused = true)]
async fn main() {
println!("Hello world");
}
Equivalent code not using #[tokio::main]
fn main() {
tokio::runtime::Builder::new_current_thread()
.enable_all()
.start_paused(true)
.build()
.unwrap()
.block_on(async {
println!("Hello world");
})
}
Note that start_paused
requires the test-util
feature to be enabled.
Rename package
use tokio as tokio1;
#[tokio1::main(crate = "tokio1")]
async fn main() {
println!("Hello world");
}
Equivalent code not using #[tokio::main]
use tokio as tokio1;
fn main() {
tokio1::runtime::Builder::new_multi_thread()
.enable_all()
.build()
.unwrap()
.block_on(async {
println!("Hello world");
})
}