A **coroutine** is used to perform multiple tasks at the same time from within
the same script. Such tasks might include producing values from inputs or
performing work on a subroutine when solving a larger problem. A task doesn't
even need to have a defined ending point, but it does need to define
particular times at which it **yields** (pause) to let other things be worked
on.

## Using Coroutines

A new coroutine can be created by providing a function to
`Library.coroutine.create()`. Once created, a coroutine doesn't begin running
until the first call to `Library.coroutine.resume()` which passes the
arguments to the function. This call returns when the function either halts or
calls `Library.coroutine.yield()` and, when this happens,
`Library.coroutine.resume()` returns either the values returned by the
function, the values sent to `Library.coroutine.yield()`, or an error message.
If it does error, the second return value is the thrown error.

```lua
local function task(...)
	-- This function might do some work for a bit then yield some value
	coroutine.yield("first")  -- To be returned by coroutine.resume()
	-- The function continues once it is resumed again
	return "second"
end

local taskCoro = coroutine.create(task)
-- Call resume for the first time, which runs the function from the beginning
local success, result = coroutine.resume(taskCoro, ...)
print(success, result)  --> true, first (task called coroutine.yield())
-- Continue running the function until it yields or halts
success, result = coroutine.resume(taskCoro)
print(success, result)  --> true, second (task halted because it returned "second")
```

During the lifetime of the coroutine, you can call
`Library.coroutine.status()` to inspect its status:

<table>
    <thead>
        <tr>
            <th>Status</th>
            <th>Meaning</th>
        </tr>
    </thead>
    <tbody>
        <tr>
            <td><b>suspended</b></td> <td>The coroutine is waiting to be
            resumed. Coroutines begin in this state and enter it when their
            function calls <code>coroutine.yield()</code>.</td>
        </tr>
        <tr>
            <td><b>running</b></td>
            <td>The coroutine is running right now.</td>
        </tr>
        <tr>
            <td><b>normal</b></td> <td>The coroutine is awaiting the yield of
            another coroutine; in other words, it has resumed another
            coroutine.</td>
        </tr>
        <tr>
            <td><b>dead</b></td> <td>The function has halted (returned or
            thrown an&nbsp;error). The coroutine cannot be used further.</td>
        </tr>
    </tbody>
</table>

### Wrapping Coroutines

When working with coroutines, you can also forgo the use of the coroutine
object and instead use a wrapper function. Such a wrapper function will resume
a particular coroutine when it is called and will return only the yielded
values. You can do this using `Library.coroutine.wrap()`:

```lua
-- Create coroutine and return a wrapper function that resumes it
local f = coroutine.wrap(task)
-- Resume the coroutine as if we called coroutine.resume()
local result = f()
-- If an error occurs it will be raised here!
-- This differs from coroutine.resume() which acts similar to pcall()
```

The first value returned from `Library.coroutine.resume()` describes whether a
coroutine ran without errors. However, functions returned by
`Library.coroutine.wrap()` will not do this: instead they directly return the
values returned or passed to `Library.coroutine.yield()`, if any. Should an
error have occurred while running the coroutine function, the error is raised
on the call of the returned function.

### Producer Pattern Example

Imagine a task that produces repetitions of a word: each time it produces a
repetition, the next one will produce one more. For example, providing `Hello`
will produce `Hello`, `HelloHello`, `HelloHelloHello`, etc. To do this, you
can define `repeatThis()`:

```lua
-- This function repeats a word every time its coroutine is resumed
local function repeatThis(word)
	local repetition = ""
	while true do
		-- Do one repetition then yield the result
		repetition = repetition .. word
		coroutine.yield(repetition)
	end
end
```

To run this function as a coroutine, you can use `Library.coroutine.create()`
followed by multiple calls to `Library.coroutine.resume()`:

```lua
local repetitionCoro = coroutine.create(repeatThis)
print(coroutine.resume(repetitionCoro, "Hello"))  -- true, Hello
print(coroutine.resume(repetitionCoro))           -- true, HelloHello
print(coroutine.resume(repetitionCoro))           -- true, HelloHelloHello
```

For this producer function, you can also use `Library.coroutine.wrap()` to get
a function that produces values:

```lua
local f = coroutine.wrap(repeatThis)
print(f("Hello"))  -- Hello
print(f())         -- HelloHello
print(f())         -- HelloHelloHello
```


Closes and puts the provided coroutine in a dead state. This function
returns `true` unless the coroutine is in an error state, in which case it
returns `false` and the error message. A coroutine that is currently
running cannot be closed. A coroutine cannot be resumed after it is
closed.


coroutine.close

`true` unless the coroutine being closed is in an error state.


Closes and puts the provided coroutine in a dead state.


Creates a new coroutine, with body f. f must be a Luau function.


coroutine.create

Returns `true` if the coroutine this function is called within can safely
yield. Yielding a coroutine inside metamethods or C functions is
prohibited, with the exception of `pcall` and `xpcall`.


coroutine.isyieldable

Whether or not the coroutine can safely yield at this point.


Returns `true` if the coroutine this function is called within can safely
yield.


Starts or continues the execution of coroutine `co`. The first time you
resume a coroutine, it starts running its body. The values `...` are
passed as the arguments to the body function. If the coroutine has
yielded, resume restarts it; the values `...` are passed as the results
from the yield. If the coroutine runs without any errors, resume returns
true plus any values passed to yield (if the coroutine yields) or any
values returned by the body function (if the coroutine terminates). If
there is any error, resume returns false plus the error message.


coroutine.resume

Starts or continues the execution of coroutine `co`.


coroutine.running

Returns the status of coroutine co, as a string: 'running', if the
coroutine is running (that is, it called status); 'suspended', if the
coroutine is suspended in a call to yield, or if it has not started
running yet; 'normal' if the coroutine is active but not running (that is,
it has resumed another coroutine); and 'dead' if the coroutine has
finished its body function, or if it has stopped with an error.


coroutine.status

Returns the status of coroutine co as a string.


Creates a new coroutine, with body f. f must be a Luau function. Returns a
function that resumes the coroutine each time it is called. Any arguments
passed to the function behave as the extra arguments to resume. Returns
the same values returned by resume, except the first boolean. In case of
error, propagates the error.


coroutine.wrap

Creates a new coroutine and returns a function that, when called, resumes
the coroutine.


Suspends the execution of the calling coroutine. Any arguments to yield
are passed as extra results to resume. Yielding a coroutine inside
metamethods or C functions is prohibited, with the exception of `pcall`
and `xpcall`.


coroutine.yield

coroutine

A function that executes alongside the main thread.


/reference/engine/libraries/coroutine.yaml

An object that runs connected functions upon a specific occurrence.

Data Type

RBXScriptSignal

Luau

Tuple

Variant

Data type having a value of either true or false.

boolean

Functions are blocks of code that can execute multiple times on command.

function

A sequence of characters, such as letters, numbers, and symbols.

string

A function that executes alongside the main thread.

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This method is asynchronous and returns an `Operation`, which represents the current state of the operation. It contains an endpoint path that you can poll to obtain the real response and applicable metadata. See the [documentation]({longRunningOperationsLink}) on long-running operations for more information.
            
The following sections describe the response and metadata objects that are provided when an operation completes.

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This endpoint can be called in-experience through {httpServiceLinkStart}HttpService{httpServiceLinkEnd} with an API key.

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These fields may be set when creating a resource, but may not be modified by subsequent requests.

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Legacy authentication method. Always prefer using API Key or OAuth 2.0 when available.

Per API Key: {maxInPeriod} requests every {periodInSeconds} seconds per IP Address

Requires no authentication to call. Typically has significantly lowered rate limits. Always prefer using API Key or OAuth 2.0 when available.

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Note: Rate limits can be lower during high-traffic periods. Certain endpoints have additional rate limits. [Learn more about rate limits]({link}).

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Scopes control what permissions your credentials have. Your credentials can only access the endpoints supported by the scopes you selected.

Stable endpoints are production-ready and will almost never experience breaking changes during their lifetime.

This target enables you to limit your key's access to selected {requiredParts}

This target enables you to limit your key's access to selected {requiredParts} and {optionalParts}

Target types are used to restrict the resources that your credentials have permissions on. Only the selected resources can be acted on even if your account has permissions on additional resources. Some scopes do not have target parts. In these cases, all of your relevant resources can be acted on.

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Authenticated requests to high-risk APIs can make changes that cannot be undone. Please review your request parameters carefully before proceeding.

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To keep your account safe, never paste text here from other sources or send information from this page to others.

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Only proceed if you understand the implications of the API calls you're about to make. Review the API documentation carefully before testing.

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This endpoint has been superseded by these recommended alternative endpoints:

The following scopes are required to call this endpoint. For more
information on generating proper keys, see [Manage API keys]({apiKeyReferenceDocLink}).

For more information on generating keys, see [Manage API keys]({apiKeyReferenceDocLink}).

The following endpoints are available at paths relative to the base URL.

This string is formatted as a [FieldMask](/cloud/reference/types#fieldmask).

A JSON value can be `null`, `boolean`, `string`, `number`, `array`, or `object`.

The following scopes are required for your OAuth 2.0 application to use this endpoint. For more information on how to register an OAuth 2.0 application, see [App registration and review]({oauth2ReferenceDocLink}).

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Resource Paths

This string is formatted as a [Timestamp](/cloud/reference/types#timestamp).

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This allows viewing information about your assets.

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