ETag Concurrency Control

This example demonstrates the built-in ETag concurrency control features of the SCIM server library, showing how to use conditional operations to prevent lost updates and handle version conflicts in multi-client scenarios.

What This Example Demonstrates

• Version-Based Conflict Prevention - Using ETags to detect and prevent concurrent modification conflicts
• Conditional Operations - HTTP-style conditional requests with If-Match and If-None-Match semantics
• Optimistic Locking - Non-blocking concurrency control for high-performance scenarios
• Conflict Resolution Patterns - Handling version mismatches and update conflicts gracefully
• Production-Ready Patterns - Real-world concurrency scenarios and best practices

Key Features Showcased

Automatic ETag Generation

See how the ResourceProvider automatically generates version identifiers for every resource, enabling precise conflict detection without manual version management.

Conditional Update Operations

Watch ConditionalOperations in action, demonstrating how to perform updates only when the expected version matches the current resource state.

Version Conflict Handling

Explore different ConditionalResult outcomes and learn how to implement proper retry logic and conflict resolution strategies.

HTTP ETag Integration

The example shows how HttpVersion and RawVersion types integrate with standard HTTP caching and conditional request mechanisms.

Concepts Explored

This example demonstrates advanced concurrency concepts:

• Concurrency Control - Complete overview of version-based conflict prevention
• Resource Providers - Provider-level concurrency implementation
• Operation Handlers - Framework integration with ETag support
• SCIM Server - Server-level concurrency orchestration

Perfect For Understanding

This example is essential if you're:

• Building Multi-Client Systems - Multiple applications updating the same resources
• Implementing Enterprise Integration - HR systems, identity providers, and applications synchronizing data
• Ensuring Data Consistency - Preventing lost updates in concurrent environments
• Production Deployment - Real-world conflict handling and resolution

Concurrency Scenarios

The example simulates realistic concurrent access patterns:

Simultaneous Updates

Two clients attempt to update the same user simultaneously, demonstrating how ETag validation prevents the "last writer wins" problem and preserves both sets of changes.

Retry Logic Implementation

Watch proper retry patterns when version conflicts occur, including exponential backoff and conflict resolution strategies.

Bulk Operation Safety

See how concurrency control applies to bulk operations, ensuring consistency across multiple resource updates.

Mixed Operation Types

The example shows how different operation types (create, read, update, delete) interact with version control mechanisms.

Version Management

Understand the complete version lifecycle:

• Version Generation - How ETags are computed from resource content
• Version Validation - Comparing expected vs. actual versions
• Version Evolution - How versions change with resource updates
• Version Exposure - Making versions available to HTTP clients

Running the Example

cargo run --example etag_concurrency_example

The output shows detailed version tracking, conflict detection, successful conditional operations, and failed operations with proper error handling - all demonstrating production-ready concurrency patterns.

Production Benefits

This example illustrates critical production capabilities:

• Data Integrity - Preventing corruption from concurrent modifications
• Performance - Non-blocking optimistic concurrency vs. expensive locking
• Scalability - Handling multiple clients without serialization bottlenecks
• Reliability - Predictable conflict detection and resolution

Integration Patterns

See how ETag concurrency integrates with:

• HTTP Frameworks - Standard If-Match/If-None-Match header handling
• Multi-Tenant Systems - Per-tenant version management
• AI Agent Operations - Version-aware automated operations
• Bulk APIs - Consistent versioning across multiple resources

Next Steps

After exploring concurrency control:

• Operation Handlers - Framework integration with conditional operations
• MCP with ETag Support - Version-aware AI agent operations
• Multi-Tenant Server - Tenant-scoped concurrency control

Source Code

View the complete implementation: examples/etag_concurrency_example.rs