Chapel Developer Hiring Guide

Hiring Guide for Chapel Engineers

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

Chapel is a parallel programming language developed by Cray Inc. with the aim of improving productivity on high-performance computing systems. It was first released in 2008 as part of the DARPA-led High Productivity Computing Systems program. Chapel supports a multithreaded execution model and offers features for both task and data parallelism, making it suitable for large-scale computations. Its design emphasizes general parallel programming, separating the concerns of parallelism and locality from algorithmic details. The language's development continues to be led by Cray, now a part of Hewlett Packard Enterprise.

First 20 minutes

General Chapel knowledge and experience

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

Describe the difference between 'in', 'out', and 'inout' intent in Chapel.

'in' intent is used when the argument is only for input, 'out' intent is used when the argument is only for output, and 'inout' intent is used when the argument is used for both input and output.

What is the purpose of the 'config' keyword in Chapel?

The 'config' keyword in Chapel is used to declare variables or constants that can be set via the command line when the program is run.

How would you write a function in Chapel?

In Chapel, a function is defined using the 'proc' keyword followed by the function name, parameters, and body. For example, 'proc add(x: int, y: int) { return x + y; }' defines a function that adds two integers.

What are the basic data types in Chapel?

Chapel supports several basic data types including integers (int), floating-point numbers (real), complex numbers (complex), boolean values (bool), and characters (char).

How would you define a variable in Chapel?

You can define a variable in Chapel using the 'var' keyword followed by the variable name and its type. For example, 'var x: int;' defines an integer variable named x.

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What youre looking for early-on

Does the candidate show a passion for Chapel and programming in general?

Passion can be a good indicator of how motivated and dedicated a candidate will be. They should show enthusiasm for Chapel and programming.

Has the candidate demonstrated an ability to learn new technologies quickly?

The tech industry is always evolving. A good developer should be able to pick up new languages and technologies quickly.

Is the candidate able to communicate effectively about their work?

Communication skills are important in any role. The candidate should be able to explain their thought process, solutions, and any challenges they encountered.

Does the candidate have experience with parallel computing?

Chapel is designed for parallel computing. Experience in this area would be a strong indicator of their ability to use the language effectively.

Can the candidate solve problems using Chapel?

Problem-solving skills are essential for any developer. The candidate should be able to use Chapel to solve complex problems.

Does the candidate have a strong understanding of Chapel language?

This is crucial as the position is for a Chapel developer. They should be able to demonstrate their knowledge and experience with the language.

Next 20 minutes

Specific Chapel development questions

The next 20 minutes of the interview should attempt to focus more specifically on the development questions used, and the level of depth and skill the engineer possesses.

What is the purpose of the 'coforall' keyword in Chapel?

The 'coforall' keyword in Chapel is used to create a concurrent loop, where each iteration of the loop is executed in a separate task.

Describe the difference between 'sync' and 'single' variables in Chapel.

'sync' variables in Chapel are used for synchronization and mutual exclusion, while 'single' variables are used for one-time assignment.

How would you write a parallel loop in Chapel?

In Chapel, you can write a parallel loop using the 'forall' keyword. For example, 'forall i in 1..n do A[i] = i;' executes the loop in parallel.

What are the different types of Chapel domains and how are they used?

Chapel has several types of domains including regular domains, irregular domains, and associative domains. Regular domains are used for arrays with regular shapes, irregular domains are used for arrays with irregular shapes, and associative domains are used for arrays with non-integer indices.

How would you create a multidimensional array in Chapel?

In Chapel, you can create a multidimensional array by defining the dimensions in the array declaration. For example, 'var A: [1..3, 1..3] int;' creates a 3x3 integer array.

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The ideal back-end app developer

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

A skilled Chapel engineer should possess strong problem-solving abilities, in-depth knowledge of parallel computing, and excellent communication skills. Red flags would include a lack of practical experience, inability to explain complex concepts clearly, or unfamiliarity with Chapel's unique features.

Digging deeper

Code questions

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

What does the following Chapel code do?

writeln('Hello, Chapel!');

This code prints the string 'Hello, Chapel!' to the standard output.

What will be the output of the following Chapel code?

var x: int = 10;
var y = 5;
var z = x + y;
writeln(z);

This code will output '15'. It declares two integer variables, x and y, assigns them the values 10 and 5 respectively, adds them together to get z, and then prints the value of z.

What does the following Chapel code do?

var A: [1..10] int;
A = 1..10;
writeln(A);

This code declares an array A of integers, assigns it the values from 1 to 10, and then prints the array.

What does the following Chapel code do?

coforall i in 1..10 {
  writeln(i);
}

This code creates a concurrent loop that prints the numbers from 1 to 10. Each iteration of the loop is a separate task that runs concurrently.

What does the following Chapel code do?

class Point {
  var x, y: real;
}
var p: Point = new Point(1.0, 2.0);
writeln(p.x, ' ', p.y);

This code defines a class 'Point' with two real variables 'x' and 'y'. It then creates an instance 'p' of the class with 'x' and 'y' values as 1.0 and 2.0 respectively. Finally, it prints the values of 'p.x' and 'p.y'.

What will be the output of the following Chapel code?

proc add(a: int, b: int): int {
  return a + b;
}
var x = add(5, 10);
writeln(x);

This code defines a procedure 'add' that takes two integer parameters and returns their sum. It then calls the procedure with arguments 5 and 10, assigns the result to variable 'x', and prints 'x'. The output will be '15'.

Wrap-up questions

Final candidate for Chapel role questions

The final few interview questions for a Chapel candidate should typically focus on a combination of technical skills, personal goals, growth potential, team dynamics, and company culture.

What are the key features of Chapel that make it suitable for high-performance computing?

Chapel has several features that make it suitable for high-performance computing including support for parallelism, concurrency, and distributed computing, a rich set of data types including distributed data structures, and a flexible and powerful syntax.

How would you implement a distributed data structure in Chapel?

In Chapel, distributed data structures can be implemented using distributed domains and arrays. For example, 'const D = new dmap(new Block(boundingBox=1..n)); var A: [D] int;' creates a distributed integer array.

Describe the difference between 'begin', 'cobegin', and 'coforall' in Chapel.

'begin' in Chapel is used to create a single asynchronous task, 'cobegin' is used to create multiple asynchronous tasks, and 'coforall' is used to create a separate task for each iteration of a loop.

What are the different ways to create tasks in Chapel?

In Chapel, tasks can be created using the 'begin', 'cobegin', and 'coforall' keywords. The 'begin' keyword creates a single task, the 'cobegin' keyword creates multiple tasks, and the 'coforall' keyword creates a task for each iteration of a loop.

How would you handle exceptions in Chapel?

In Chapel, exceptions are handled using 'try', 'catch', and 'throw' keywords. The 'try' block contains the code that might throw an exception, the 'catch' block contains the code to handle the exception, and the 'throw' keyword is used to throw an exception.

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Chapel application related

Product Perfect's Chapel development capabilities

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

Chapel Consultive assessments

Custom Chapel development projects

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