Hiring guide for Cilk Engineers

Cilk Developer Hiring Guide

Cilk is a general-purpose programming language designed for multithreaded parallel computing, originally developed at the Massachusetts Institute of Technology (MIT) in 1994. It extends C and C++ languages to include constructs that facilitate parallel computing, making it easier for programmers to write efficient, scalable multithreaded programs. The development of this language was led by notable computer scientist Charles E. Leiserson from MIT's Computer Science and Artificial Intelligence Laboratory (CSAIL). Today, its most popular version is included in the Intel C++ Compiler as "Cilk Plus", which continues to be widely used in high-performance computing applications.

Ask the right questions secure the right Cilk talent among an increasingly shrinking pool of talent.

First 20 minutes

General Cilk app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Cilk application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

How would you define Cilk?
Cilk is a general-purpose programming language designed for multithreaded parallel computing. It's an extension of C and C++ and provides high-level constructs for parallel execution.
What are the key features of Cilk?
Cilk includes features like efficient handling of task parallelism, support for nested parallelism, work-stealing scheduling algorithm, and exception handling mechanisms.
Describe the difference between Cilk and other parallel programming languages.
Cilk is designed to be easy to use and to seamlessly handle the complexities of parallel processing. It provides a simple yet powerful model for parallel programming, unlike other languages that require explicit management of threads and synchronization.
How would you implement a parallel for loop in Cilk?
In Cilk, a parallel for loop can be implemented using the cilk_for keyword. This automatically divides the loop iterations among available processors.
What are the main components of a Cilk program?
A Cilk program consists of functions, which can be either Cilk functions or C functions. Cilk functions can execute in parallel, while C functions execute serially.
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What you’re looking for early on

Does the candidate have a strong understanding of Cilk's parallel programming model?
Has the candidate demonstrated experience with Cilk's work-stealing scheduler?
Is the candidate comfortable with Cilk's syntax and language constructs?
Has the candidate shown problem-solving skills and the ability to think in parallel?

Next 20 minutes

Specific Cilk development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

Describe the difference between cilk_spawn and cilk_sync in Cilk.
cilk_spawn is used to create a new task that can execute in parallel with the current task. cilk_sync is used to wait for all spawned tasks to complete.
How would you handle exceptions in a Cilk program?
Cilk provides a mechanism for exception handling similar to that in C++. If an exception is thrown in a Cilk function, it propagates up to the nearest enclosing cilk_sync.
What are the benefits of using the work-stealing scheduling algorithm in Cilk?
The work-stealing scheduling algorithm allows for efficient load balancing across processors. It also minimizes communication between processors, leading to better performance.
How would you debug a Cilk program?
Cilk provides a tool called Cilkscreen to help debug Cilk programs. It can detect common parallel programming errors like race conditions and deadlocks.
What are the limitations of Cilk?
Cilk does not support data parallelism directly. Also, it does not provide explicit control over thread creation and synchronization, which can be a limitation for some applications.
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The ideal back-end app developer

What you’re looking to see on the Cilk engineer at this point.

At this point, a skilled Cilk engineer should demonstrate strong problem-solving abilities, proficiency in Cilk programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Cilk.

What does this simple Cilk code do?
cilk int fib(int n) {
  if (n < 2) return n;
  int x = cilk_spawn fib(n-1);
  int y = fib(n-2);
  return x + y;
This code calculates the Fibonacci number of a given integer 'n' using Cilk's parallel processing capabilities. It uses the 'cilk_spawn' keyword to create a new task for the calculation of 'fib(n-1)' and 'cilk_sync' to wait for all spawned tasks to complete before proceeding.
What will be the output of this Cilk code?
cilk int main() {
  cilk_for (int i = 0; i < 5; i++) {
    printf("%d\n", i);
  return 0;
The output of this code will be the numbers 0 to 4, each printed on a new line. The 'cilk_for' loop is a parallel loop that executes the iterations in any order, but in this case, the output will always be in ascending order because there is no dependency between iterations.
What does this Cilk code do with an array?
cilk void array_sum(int* arr, int n) {
  int sum = 0;
  cilk_for (int i = 0; i < n; i++) {
    sum += arr[i];
  printf("Sum: %d\n", sum);
This code calculates the sum of all elements in an integer array 'arr' of size 'n'. It uses a 'cilk_for' loop to add each element to the 'sum' variable in parallel. The sum is then printed to the console.
What does this Cilk code do with threads?
cilk int main() {
  cilk_spawn printf("Hello, ");
  return 0;
This code prints 'Hello, world!' to the console. It uses 'cilk_spawn' to create a new task for printing 'Hello, ', and 'cilk_sync' to wait for all spawned tasks to complete before proceeding. The order of the words may vary due to the parallel execution of the tasks.

Wrap-up questions

Final candidate for Cilk Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Cilk application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

How would you optimize a Cilk program for performance?
Performance optimization in Cilk involves minimizing synchronization overhead, maximizing parallelism, and ensuring efficient use of memory. This can be achieved by careful task decomposition and efficient data structures.
Describe the difference between Cilk Plus and Cilk.
Cilk Plus is an extension of Cilk that includes additional features like array notations for data parallelism, and reducers for safe parallel updates to shared variables.
How would you handle shared variables in a Cilk program?
Cilk provides a mechanism called reducers for safe parallel updates to shared variables. A reducer is a special kind of variable that can be safely updated by multiple tasks in parallel.

Cilk application related

Product Perfect's Cilk development capabilities

Beyond hiring for your Cilk engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Cilk projects, and can engage in multiple capacities.