What are Synchronous and Asynchronous API Calls?  

A synchronous API call is a blocking operation, which means that the thread that initiates the call will wait and be unavailable for other tasks until it receives a response or the request times out. In a synchronous REST API call, the client sends a request to the server and must wait (blocking) until the server processes the request and returns a response. During this time, the client is unable to perform any other tasks. 

In contrast, an asynchronous API call is non-blocking. The thread making the call can continue executing other code, which allows for more efficient handling of concurrent tasks. With an asynchronous REST API call, the client sends a request to the server and continues executing other tasks without waiting for the response. The server processes the request and returns a response at a later time. 

Client Behavior  

In a synchronous call, the client is blocked and must wait for the server’s response. This approach is appropriate for scenarios where an immediate response is necessary for the client to proceed, such as when retrieving data required immediately.  

In contrast, with an asynchronous call, the client is not blocked and can continue executing other operations or handling different tasks. This method is well-suited for operations that might take a long time to complete, like file processing or database updates, where the client doesn’t need an immediate response. 

Use Cases  

Synchronous calls are best suited for real-time operations where the client requires an immediate response, such as querying a database for information or performing straightforward transactions. These calls are typically used in CRUD (Create, Read, Update, Delete) operations, where the client anticipates an immediate response from the server.  

On the other hand, asynchronous calls are ideal for long-running tasks like large-scale data processing, file uploads or downloads, sending emails, or other time-consuming operations. They are commonly utilized in microservices architectures, enabling services to communicate without blocking, which improves scalability and responsiveness. 

Implementation Complexity  

Synchronous API calls are simpler to implement because of their straightforward nature, and most frameworks support them without needing advanced techniques. In contrast, asynchronous API calls are more complex to implement and require a strong grasp of asynchronous programming concepts, such as callbacks and promises. Additionally, they involve extra logic to manage response callbacks, timeouts, retries, and error handling. 

Pros of Synchronous REST API Calls  

• Simplicity and Ease of Implementation: Synchronous calls are easy to implement, making them accessible for developers and well supported by most frameworks. 

• Predictable Flow: The execution flow is linear and predictable, which simplifies reasoning about the sequence of operations and makes debugging more straightforward.  

• Simplified Error Handling: Error handling is more straightforward since errors are returned immediately and can be caught directly within the request-response cycle. This reduces the need to manage multiple error states or callbacks, minimizing the complexity of error management. 

Cons of Synchronous REST API Calls 

• Blocking Behavior: Synchronous calls block the client or thread until the server responds, which can lead to poor performance and a subpar user experience, particularly if the server takes a long time to reply.  

• Scalability Limitations: The blocking nature of synchronous calls consumes resources, such as threads, while waiting for the server to respond. This can hinder scalability, especially in high-traffic environments or when handling long-running operations.  

• Inefficient Resource Utilization: System resources, like threads, remain idle while waiting for a response, leading to inefficient use of resources and reduced application throughput. 

Pros of Asynchronous REST API Calls 

• Non-Blocking Execution: Asynchronous calls allow the client or server thread to continue executing other tasks while waiting for a response, enhancing application responsiveness and improving the user experience. This is especially advantageous in client-side applications, where the UI remains responsive even while waiting for data from the server.  

• Improved Scalability: Asynchronous calls enable applications to manage a higher volume of concurrent requests without consuming additional threads or blocking resources, making them ideal for handling heavy traffic and long-running operations without sacrificing performance. 

• Ideal for Background Processing: Asynchronous calls are well-suited for tasks that can be processed in the background, such as batch processing, scheduled tasks, or data synchronization, allowing the main application thread to remain free for other tasks. 

Cons of Asynchronous REST API Calls 

• Increased Complexity: Asynchronous programming adds complexity to the code structure, often requiring the use of callbacks, promises, or async/await patterns. This can make the code more difficult to read, write, and maintain.  

• Challenging Debugging: Debugging asynchronous code can be more difficult because errors may not surface immediately, and stack traces may not clearly point to the source of the issue. This can make it harder to trace problems back to their origin, as asynchronous errors can occur at any time, complicating the reproduction and diagnosis of issues. Proper synchronization and locking mechanisms are also required to ensure data integrity, further adding to the complexity.  

• Testing Challenges: Testing asynchronous code is more complex than testing synchronous code, requiring additional tools and frameworks to effectively simulate asynchronous operations and handle promises or async/await patterns. 

Conclusion 

Synchronous REST API calls are simpler and block the client until a response is received, making them suitable for quick, straightforward tasks. Asynchronous REST API calls are more complex but allow the client to continue executing other tasks while waiting for a response, making them ideal for long-running operations or when improved responsiveness and scalability are required. The choice between synchronous and asynchronous API calls depends on the specific use case, real-time processing needs, and the requirements for system efficiency and scalability.  

NetSuite ERP provides a range of APIs that allow external applications and systems to communicate with its services. As a NetSuite partner, SuiteMatrix helps businesses streamline operations by implementing custom API integrations and automating key processes, ensuring seamless data flow and improved efficiency across all systems.