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Architecture

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This page shows go-scheduler's component layers and cross-cutting principles in a single overview diagram.

System Overview

graph TB
    App[Caller] --> Cron[cron scheduler]
    Cron --> Parser[Expression parser]
    Cron --> Heap[Task min-heap]
    Heap --> Loop[Event loop goroutine]
    Loop -->|no deps| Direct[Direct goroutine run]
    Loop -->|has deps| Queue[Wait queue]
    Queue --> Workers[Dependency worker pool]
    Workers --> Manager[dependManager]
    Direct --> State[Task state]
    Manager --> State

Layers

Layer Component Files Responsibility
Public interface cron core/instance.go, core/add.go, core/remove.go, core/task.go New / Start / Stop / Add / Remove / RemoveAll / List
Parsing parser core/schedule.go Turns a spec into scheduleResult (cron, descriptors) or delayScheduleResult (@every)
Scheduling taskHeap core/task.go Min-heap ordered by next; the event loop only waits on the top entry
Execution cron.runAfter core/instance.go Tasks without dependencies: goroutine run, timeout, panic recovery
Dependencies depend, dependManager core/depend.go, core/dependManager.go Queue (capacity 1024), worker pool, prerequisite polling, result updates

Cross-Cutting Principles

Principle Implementation
One event loop owns the heap After Start, add, remove, and clear go through the add / remove / removeAll channels; before Start the heap is modified directly
Per-task locking Each task holds a sync.RWMutex; dependency checks read prerequisite state under a read lock
Dependent and plain tasks are split cron.run runs directly or enqueues to the worker pool based on whether after is empty
Bounded worker count runtime.NumCPU() when greater than 2, otherwise 2
Shutdown does not interrupt actions Stop waits for the WaitGroup and workers; actions do not receive a context

Further Reading

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