The spawn expression starts one async function invocation, and any expression that follows the spawn is executed immediately while the started async function task continues independently until it completes.
# Continues until completed without blocking
spawn{AsyncFunction1()} # Started at same time as expression0
expression0 # Started at same time as AsyncFunction1()
The following code shows the syntax for the spawn expression.
expression0
spawn{ expression1 }
expression2
The diagram below shows the execution flow of the expressions.
While similar to branch, the spawn body is limited to a single async function call. It is also allowed outside of an async context, so it can be called within both non-async and async functions.
A spawn expression should be treated like an emergency escape hatch, while branch should be used in place of spawn whenever possible.
Spawn Expression Use
Where you can use a spawn expression |
Any context. |
Invocation time of the spawn expression |
Immediate. |
Requirements for spawn code block |
The body of the spawn expression is started as soon as it is encountered. It must have at least one async expression. |
What the spawn expression does |
The body of a spawn creates an async context like the body of an async function. However, only a single async function call is allowed within the spawn body. The async function of the spawn is started as soon as it is encountered, and evaluates as much as possible until it encounters something suspending or blocking. The spawned async function continues to evaluate until it completes without any further connection to the location where it was spawned. |
When the spawn expression completes |
The spawn expression completes immediately. |
When the next expression after spawn starts |
Any next expression that follows the spawn expression is started immediately. |
Result of the spawn expression |
A spawn has a task result. |