job-state-machine

Development

Async job processing with validated state transitions, progress tracking, and asset linking. Ensure jobs always reach terminal states with proper error handling.

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Job State Machine

Validated state transitions for async jobs.

When to Use This Skill

Processing async jobs (image generation, exports, etc.)
Need progress tracking for long operations
Want to link created assets to jobs
Need reliable state management

Core Concepts

Defined states - QUEUED → PROCESSING → COMPLETED/FAILED/PARTIAL
Valid transitions - Only allowed state changes
Terminal states - Jobs must reach an end state
Asset linking - Track outputs created by jobs

State Machine

         QUEUED
            │
            ▼
       PROCESSING
       /    |    \
      ▼     ▼     ▼
COMPLETED PARTIAL FAILED
   (terminal states)

TypeScript Implementation

Types

// types.ts
export enum JobStatus {
  QUEUED = 'queued',
  PROCESSING = 'processing',
  COMPLETED = 'completed',
  FAILED = 'failed',
  PARTIAL = 'partial',
}

export const VALID_TRANSITIONS: Record<JobStatus, JobStatus[]> = {
  [JobStatus.QUEUED]: [JobStatus.PROCESSING],
  [JobStatus.PROCESSING]: [JobStatus.COMPLETED, JobStatus.PARTIAL, JobStatus.FAILED],
  [JobStatus.COMPLETED]: [],
  [JobStatus.FAILED]: [],
  [JobStatus.PARTIAL]: [],
};

export function isTerminalState(status: JobStatus): boolean {
  return VALID_TRANSITIONS[status].length === 0;
}

export interface Job {
  id: string;
  userId: string;
  jobType: string;
  status: JobStatus;
  progress: number;
  errorMessage?: string;
  parameters?: Record<string, unknown>;
  result?: Record<string, unknown>;
  createdAt: Date;
  updatedAt: Date;
  completedAt?: Date;
}

export interface Asset {
  id: string;
  jobId: string;
  userId: string;
  assetType: string;
  url: string;
  storagePath: string;
  fileSize: number;
  createdAt: Date;
}

Job Service

// job-service.ts
import { Job, JobStatus, Asset, VALID_TRANSITIONS, isTerminalState } from './types';

export class InvalidStateTransitionError extends Error {
  constructor(public currentStatus: JobStatus, public targetStatus: JobStatus) {
    super(`Cannot transition from '${currentStatus}' to '${targetStatus}'`);
    this.name = 'InvalidStateTransitionError';
  }
}

export class JobService {
  constructor(private db: Database) {}

  async createJob(
    userId: string,
    jobType: string,
    parameters?: Record<string, unknown>
  ): Promise<Job> {
    const job: Job = {
      id: crypto.randomUUID(),
      userId,
      jobType,
      status: JobStatus.QUEUED,
      progress: 0,
      parameters,
      createdAt: new Date(),
      updatedAt: new Date(),
    };

    await this.db.jobs.insert(job);
    return job;
  }

  async getJob(jobId: string, userId: string): Promise<Job> {
    const job = await this.db.jobs.findOne({ id: jobId });
    if (!job) throw new Error('Job not found');
    if (job.userId !== userId) throw new Error('Unauthorized');
    return job;
  }

  async transitionStatus(
    jobId: string,
    targetStatus: JobStatus,
    options: {
      progress?: number;
      errorMessage?: string;
      result?: Record<string, unknown>;
    } = {}
  ): Promise<Job> {
    const job = await this.db.jobs.findOne({ id: jobId });
    if (!job) throw new Error('Job not found');

    // Allow same-state for progress updates
    if (job.status !== targetStatus) {
      if (!VALID_TRANSITIONS[job.status].includes(targetStatus)) {
        throw new InvalidStateTransitionError(job.status, targetStatus);
      }
    }

    const updates: Partial<Job> = {
      status: targetStatus,
      progress: options.progress ?? job.progress,
      updatedAt: new Date(),
    };

    if (options.errorMessage !== undefined) {
      updates.errorMessage = options.errorMessage;
    }

    if (options.result !== undefined) {
      updates.result = options.result;
    }

    if (isTerminalState(targetStatus)) {
      updates.completedAt = new Date();
    }

    await this.db.jobs.update({ id: jobId }, updates);
    return { ...job, ...updates };
  }

  async updateProgress(jobId: string, progress: number): Promise<Job> {
    const job = await this.db.jobs.findOne({ id: jobId });
    if (!job) throw new Error('Job not found');

    if (job.status !== JobStatus.PROCESSING) {
      console.warn(`Ignoring progress update for job ${jobId} in ${job.status} state`);
      return job;
    }

    return this.transitionStatus(jobId, JobStatus.PROCESSING, { progress });
  }

  async markCompleted(jobId: string, result?: Record<string, unknown>): Promise<Job> {
    return this.transitionStatus(jobId, JobStatus.COMPLETED, { progress: 100, result });
  }

  async markFailed(jobId: string, errorMessage: string): Promise<Job> {
    return this.transitionStatus(jobId, JobStatus.FAILED, { errorMessage });
  }

  async markPartial(
    jobId: string,
    result?: Record<string, unknown>,
    errorMessage?: string
  ): Promise<Job> {
    return this.transitionStatus(jobId, JobStatus.PARTIAL, {
      progress: 100,
      result,
      errorMessage,
    });
  }

  async createAsset(
    jobId: string,
    userId: string,
    assetType: string,
    url: string,
    storagePath: string,
    fileSize: number
  ): Promise<Asset> {
    const asset: Asset = {
      id: crypto.randomUUID(),
      jobId,
      userId,
      assetType,
      url,
      storagePath,
      fileSize,
      createdAt: new Date(),
    };

    await this.db.assets.insert(asset);
    return asset;
  }

  async getJobAssets(jobId: string, userId: string): Promise<Asset[]> {
    await this.getJob(jobId, userId); // Verify ownership
    return this.db.assets.find({ jobId });
  }
}

Python Implementation

# job_service.py
from enum import Enum
from dataclasses import dataclass
from datetime import datetime
from typing import Optional, Dict, Any, List
from uuid import uuid4

class JobStatus(str, Enum):
    QUEUED = "queued"
    PROCESSING = "processing"
    COMPLETED = "completed"
    FAILED = "failed"
    PARTIAL = "partial"

VALID_TRANSITIONS = {
    JobStatus.QUEUED: [JobStatus.PROCESSING],
    JobStatus.PROCESSING: [JobStatus.COMPLETED, JobStatus.PARTIAL, JobStatus.FAILED],
    JobStatus.COMPLETED: [],
    JobStatus.FAILED: [],
    JobStatus.PARTIAL: [],
}

def is_terminal_state(status: JobStatus) -> bool:
    return len(VALID_TRANSITIONS.get(status, [])) == 0

@dataclass
class Job:
    id: str
    user_id: str
    job_type: str
    status: JobStatus
    progress: int
    created_at: datetime
    updated_at: datetime
    error_message: Optional[str] = None
    parameters: Optional[Dict[str, Any]] = None
    result: Optional[Dict[str, Any]] = None
    completed_at: Optional[datetime] = None

class InvalidStateTransitionError(Exception):
    def __init__(self, current: JobStatus, target: JobStatus):
        self.current = current
        self.target = target
        super().__init__(f"Cannot transition from '{current}' to '{target}'")

class JobService:
    def __init__(self, db):
        self.db = db

    async def create_job(
        self,
        user_id: str,
        job_type: str,
        parameters: Optional[Dict[str, Any]] = None,
    ) -> Job:
        now = datetime.utcnow()
        job = Job(
            id=str(uuid4()),
            user_id=user_id,
            job_type=job_type,
            status=JobStatus.QUEUED,
            progress=0,
            parameters=parameters,
            created_at=now,
            updated_at=now,
        )
        await self.db.jobs.insert(job)
        return job

    async def transition_status(
        self,
        job_id: str,
        target_status: JobStatus,
        progress: Optional[int] = None,
        error_message: Optional[str] = None,
        result: Optional[Dict[str, Any]] = None,
    ) -> Job:
        job = await self.db.jobs.find_one(id=job_id)
        if not job:
            raise ValueError("Job not found")

        if job.status != target_status:
            if target_status not in VALID_TRANSITIONS.get(job.status, []):
                raise InvalidStateTransitionError(job.status, target_status)

        job.status = target_status
        job.updated_at = datetime.utcnow()
        
        if progress is not None:
            job.progress = progress
        if error_message is not None:
            job.error_message = error_message
        if result is not None:
            job.result = result
        if is_terminal_state(target_status):
            job.completed_at = datetime.utcnow()

        await self.db.jobs.update(job)
        return job

    async def mark_completed(self, job_id: str, result: Optional[Dict] = None) -> Job:
        return await self.transition_status(
            job_id, JobStatus.COMPLETED, progress=100, result=result
        )

    async def mark_failed(self, job_id: str, error_message: str) -> Job:
        return await self.transition_status(
            job_id, JobStatus.FAILED, error_message=error_message
        )

Worker Integration

async function processJob(jobId: string) {
  const jobService = getJobService();

  try {
    // Transition to PROCESSING
    await jobService.transitionStatus(jobId, JobStatus.PROCESSING, { progress: 0 });

    const job = await jobService.getJobInternal(jobId);

    // Process with progress updates
    await jobService.updateProgress(jobId, 25);
    const result1 = await doStep1(job.parameters);

    await jobService.updateProgress(jobId, 50);
    const result2 = await doStep2(result1);

    await jobService.updateProgress(jobId, 75);
    const assetUrl = await uploadResult(result2);

    // Create asset
    await jobService.createAsset(
      jobId,
      job.userId,
      job.jobType,
      assetUrl,
      `${job.userId}/${jobId}/result.png`,
      result2.length
    );

    // Mark completed
    await jobService.markCompleted(jobId, { assetCount: 1 });

  } catch (error) {
    console.error(`Job ${jobId} failed:`, error);
    await jobService.markFailed(jobId, error.message);
  }
}

Database Schema

CREATE TABLE jobs (
    id UUID PRIMARY KEY,
    user_id UUID NOT NULL REFERENCES users(id),
    job_type VARCHAR(50) NOT NULL,
    status VARCHAR(20) NOT NULL DEFAULT 'queued',
    progress INTEGER NOT NULL DEFAULT 0,
    error_message TEXT,
    parameters JSONB,
    result JSONB,
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW(),
    completed_at TIMESTAMPTZ,
    
    CONSTRAINT valid_status CHECK (status IN ('queued', 'processing', 'completed', 'failed', 'partial')),
    CONSTRAINT valid_progress CHECK (progress >= 0 AND progress <= 100)
);

CREATE INDEX idx_jobs_user_status ON jobs(user_id, status);

CREATE TABLE assets (
    id UUID PRIMARY KEY,
    job_id UUID NOT NULL REFERENCES jobs(id) ON DELETE CASCADE,
    user_id UUID NOT NULL REFERENCES users(id),
    asset_type VARCHAR(50) NOT NULL,
    url TEXT NOT NULL,
    storage_path TEXT NOT NULL,
    file_size INTEGER NOT NULL,
    created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
);

CREATE INDEX idx_assets_job_id ON assets(job_id);

Best Practices

Validate all transitions - Never skip state machine validation
Always reach terminal - Jobs must complete, fail, or partial
Track progress - Provide feedback for long operations
Link assets - Maintain relationship for cleanup
Log transitions - Essential for debugging

Common Mistakes

Allowing invalid state transitions
Jobs stuck in non-terminal states
Not tracking progress for long jobs
Orphaned assets without job links
Missing error messages on failure