---
url: /api/scripts/extension-modules/core/base/scheduler.md
---
# scheduler

The scheduler module provides coroutine scheduling functionality for managing coroutine creation, execution, synchronization, and communication. This is an extension module of xmake.

::: tip NOTE
To use this module, you need to import it first: `import("core.base.scheduler")`
:::

## scheduler.co\_start

* Start a new coroutine task

#### Function Prototype

::: tip API

```lua
scheduler.co_start(cotask: <function>, ...)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| cotask | Required. The coroutine task function to execute |
| ... | Optional. Arguments to pass to the task function |

#### Return Value

| Type | Description |
|------|-------------|
| coroutine | Returns coroutine object |

#### Usage

Start a new coroutine and execute the specified task function. The coroutine will start executing immediately unless the scheduler is not yet started.

```lua
-- Start coroutine with arguments
local co = scheduler.co_start(function(name, id)
    print("Task", name, "with id", id, "started")
end, "worker", 123)

-- Coroutine group example
local count = 0
scheduler.co_group_begin("test", function()
    for i = 1, 100 do
        scheduler.co_start(function()
            count = count + 1
        end)
    end
end)
scheduler.co_group_wait("test")
print("Completed", count, "tasks")
```

## scheduler.co\_start\_named

* Start a named coroutine task

#### Function Prototype

::: tip API

```lua
scheduler.co_start_named(coname: <string>, cotask: <function>, ...)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| coname | Required. Coroutine name |
| cotask | Required. The coroutine task function to execute |
| ... | Optional. Arguments to pass to the task function |

#### Usage

Start a coroutine task with a specified name for easier debugging and monitoring.

```lua
-- Start multiple named coroutines
for i = 1, 5 do
    scheduler.co_start_named("worker-" .. i, function()
        print("Worker", i, "started")
        scheduler.co_sleep(1000)
        print("Worker", i, "finished")
    end)
end
```

## scheduler.co\_start\_withopt

* Start a coroutine task with options

#### Function Prototype

::: tip API

```lua
scheduler.co_start_withopt(opt: <table>, cotask: <function>, ...)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| opt | Required. Coroutine options table |
| cotask | Required. The coroutine task function to execute |
| ... | Optional. Arguments to pass to the task function |

#### Usage

Start a coroutine task with specific options.

`opt` options:

* `name` - Coroutine name
* `isolate` - Whether to isolate coroutine environment (default false)

```lua
-- Start coroutine with isolated environment
local co = scheduler.co_start_withopt({
    name = "isolated-task",
    isolate = true
}, function()
    -- This coroutine has independent environment variables
    os.setenv("CUSTOM_VAR", "isolated_value")
    print("Isolated task running")
end)
```

## scheduler.co\_suspend

* Suspend the current coroutine

#### Function Prototype

::: tip API

```lua
scheduler.co_suspend()
```

:::

#### Parameter Description

No parameters required for this function.

#### Return Value

| Type | Description |
|------|-------------|
| any | Returns arguments passed to `co_resume` |

#### Usage

Suspend the currently executing coroutine and yield execution to other coroutines.

```lua
local co = scheduler.co_start(function()
    print("Step 1")
    scheduler.co_suspend()
    print("Step 2")
end)

-- Coroutine will suspend at co_suspend()
-- Can be resumed with co_resume
```

## scheduler.co\_resume

* Resume a suspended coroutine

#### Function Prototype

::: tip API

```lua
scheduler.co_resume(co: <coroutine>, ...)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| co | Required. The coroutine object to resume |
| ... | Optional. Arguments to pass to the coroutine |

#### Usage

Resume the specified suspended coroutine and optionally pass arguments to it.

```lua
-- Coroutine communication example
local co = scheduler.co_start(function()
    local data = scheduler.co_suspend()
    print("Received data:", data)
    local result = "processed: " .. data
    scheduler.co_suspend(result)
end)

-- Send data and get result
scheduler.co_resume(co, "input data")
local result = scheduler.co_resume(co)
print("Got result:", result)
```

## scheduler.co\_yield

* Yield execution of the current coroutine

#### Function Prototype

::: tip API

```lua
scheduler.co_yield()
```

:::

#### Parameter Description

No parameters required for this function.

#### Usage

Yield execution of the current coroutine to allow other coroutines to run. This is a key function for cooperative multitasking.

```lua
-- Cooperative task example
scheduler.co_group_begin("cooperative", function()
    for i = 1, 3 do
        scheduler.co_start(function(id)
            for j = 1, 3 do
                print("Task", id, "step", j)
                scheduler.co_yield()
            end
        end, i)
    end
end)
scheduler.co_group_wait("cooperative")
```

## scheduler.co\_sleep

* Sleep the coroutine for specified time

#### Function Prototype

::: tip API

```lua
scheduler.co_sleep(ms: <number>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| ms | Required. Sleep time in milliseconds, 0 means no sleep |

#### Usage

Make the current coroutine sleep for the specified number of milliseconds, during which other coroutines can continue executing.

```lua
-- Timed task example
for i = 1, 5 do
    scheduler.co_start(function(id)
        print("Task", id, "starting")
        scheduler.co_sleep(id * 500)  -- Incremental delay
        print("Task", id, "finished")
    end, i)
end
```

## scheduler.co\_lock

* Lock the specified lock

#### Function Prototype

::: tip API

```lua
scheduler.co_lock(lockname: <string>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| lockname | Required. The name of the lock |

#### Usage

Acquire the lock with the specified name. If the lock is already held by another coroutine, the current coroutine will wait until the lock becomes available.

```lua
-- Mutex lock example
local shared_counter = 0

for i = 1, 10 do
    scheduler.co_start(function(id)
        scheduler.co_lock("counter")
        local old_value = shared_counter
        scheduler.co_sleep(100)  -- Simulate work
        shared_counter = old_value + 1
        print("Task", id, "incremented counter to", shared_counter)
        scheduler.co_unlock("counter")
    end, i)
end
```

## scheduler.co\_unlock

* Release the specified lock

#### Function Prototype

::: tip API

```lua
scheduler.co_unlock(lockname: <string>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| lockname | Required. The name of the lock to release |

#### Usage

Release the lock with the specified name, allowing other waiting coroutines to acquire the lock.

## scheduler.co\_group\_begin

* Begin a coroutine group

#### Function Prototype

::: tip API

```lua
scheduler.co_group_begin(name: <string>, scopefunc: <function>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| name | Required. The coroutine group name |
| scopefunc | Required. The scope function |

#### Usage

Begin a new coroutine group. All coroutines started within the specified function will join this group.

```lua
-- Batch job processing example
scheduler.co_group_begin("batch_jobs", function()
    local jobs = {"job1", "job2", "job3", "job4", "job5"}
    for i, job in ipairs(jobs) do
        scheduler.co_start(function(job_name)
            print("Processing", job_name)
            scheduler.co_sleep(math.random(100, 500))
            print("Completed", job_name)
        end, job)
    end
end)
```

## scheduler.co\_group\_wait

* Wait for coroutine group completion

#### Function Prototype

::: tip API

```lua
scheduler.co_group_wait(name: <string>, opt: <table>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| name | Required. The coroutine group name |
| opt | Optional. Wait options |

`opt` options:

* `limit` - Maximum number of coroutines to wait for completion (default wait for all coroutines)

#### Usage

Wait for all coroutines in the specified group to complete execution.

```lua
-- Limited wait example
scheduler.co_group_begin("limited", function()
    for i = 1, 10 do
        scheduler.co_start(function(id)
            print("Task", id, "running")
            scheduler.co_sleep(id * 100)
            print("Task", id, "finished")
        end, i)
    end
end)

-- Only wait for first 3 coroutines to complete
scheduler.co_group_wait("limited", {limit = 3})
print("First 3 tasks completed")
```

## scheduler.co\_running

* Get the currently running coroutine

#### Function Prototype

::: tip API

```lua
scheduler.co_running()
```

:::

#### Parameter Description

No parameters required for this function.

#### Return Value

| Type | Description |
|------|-------------|
| coroutine | Current coroutine object (nil if no coroutine is running) |

#### Usage

Get the currently running coroutine object.

```lua
-- Coroutine info example
scheduler.co_start_named("info_task", function()
    local co = scheduler.co_running()
    print("Coroutine name:", co:name())
    print("Coroutine status:", co:status())
    print("Is dead:", co:is_dead())
    print("Is running:", co:is_running())
    print("Is suspended:", co:is_suspended())
end)
```

## scheduler.co\_count

* Get the total number of coroutines

#### Function Prototype

::: tip API

```lua
scheduler.co_count()
```

:::

#### Parameter Description

No parameters required for this function.

#### Return Value

| Type | Description |
|------|-------------|
| number | Number of coroutines |

#### Usage

Get the total number of active coroutines in the current scheduler.

```lua
-- Coroutine counting example
print("Initial count:", scheduler.co_count())

for i = 1, 5 do
    scheduler.co_start(function()
        print("Task", i, "started, count:", scheduler.co_count())
        scheduler.co_sleep(1000)
        print("Task", i, "finished, count:", scheduler.co_count())
    end)
end

print("After starting tasks:", scheduler.co_count())
```

## scheduler.co\_semaphore

* Create a coroutine semaphore

#### Function Prototype

::: tip API

```lua
scheduler.co_semaphore(name: <string>, value: <number>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| name | Required. Semaphore name |
| value | Optional. Initial semaphore value (default 0) |

#### Return Value

| Type | Description |
|------|-------------|
| semaphore | Semaphore object |

#### Usage

Create a new coroutine semaphore for synchronization and resource control between coroutines.

```lua
-- Semaphore example
local semaphore = scheduler.co_semaphore("resource", 3)  -- Allow up to 3 coroutines simultaneously

for i = 1, 10 do
    scheduler.co_start(function(id)
        print("Task", id, "waiting for resource")
        local value = semaphore:wait(-1)  -- Wait indefinitely
        print("Task", id, "got resource, value:", value)
        scheduler.co_sleep(1000)  -- Simulate work
        semaphore:post(1)  -- Release resource
        print("Task", id, "released resource")
    end, i)
end
```

## co\_semaphore:wait

* Wait for semaphore

#### Function Prototype

::: tip API

```lua
co_semaphore:wait(timeout: <number>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| timeout | Optional. Timeout in milliseconds, -1 means wait indefinitely, 0 means don't wait |

#### Return Value

| Type | Description |
|------|-------------|
| number | Returns semaphore value |

#### Usage

Wait for the semaphore. If the semaphore value is greater than 0, return immediately; otherwise, suspend the current coroutine until the semaphore becomes available.

```lua
-- Semaphore wait example
local semaphore = scheduler.co_semaphore("worker", 0)

-- Producer coroutine
scheduler.co_start(function()
    for i = 1, 5 do
        scheduler.co_sleep(1000)
        semaphore:post(1)
        print("Posted signal", i)
    end
end)

-- Consumer coroutine
scheduler.co_start(function()
    for i = 1, 5 do
        local value = semaphore:wait(-1)
        print("Got signal", i, "value:", value)
    end
end)
```

## co\_semaphore:post

* Release semaphore

#### Function Prototype

::: tip API

```lua
co_semaphore:post(value: <number>)
```

:::

#### Parameter Description

| Parameter | Description |
|-----------|-------------|
| value | Required. The value to increase by |

#### Return Value

| Type | Description |
|------|-------------|
| number | The new semaphore value after release |

#### Usage

Release the semaphore by increasing its value and wake up waiting coroutines.

```lua
-- Semaphore post example
local semaphore = scheduler.co_semaphore("batch", 0)

-- Batch processing example
scheduler.co_start(function()
    scheduler.co_sleep(2000)
    print("Batch processing started")
    semaphore:post(5)  -- Release 5 signals at once
end)

for i = 1, 5 do
    scheduler.co_start(function(id)
        local value = semaphore:wait(-1)
        print("Worker", id, "got batch signal, value:", value)
    end, i)
end
```

## co\_semaphore:name

* Get semaphore name

#### Function Prototype

::: tip API

```lua
co_semaphore:name()
```

:::

#### Parameter Description

No parameters required for this function.

#### Return Value

| Type | Description |
|------|-------------|
| string | Semaphore name string |

#### Usage

Get the semaphore name.