Hiring guide for Charm++. Engineers

Charm++. Developer Hiring Guide

Charm++ is an advanced parallel object-oriented programming language, developed by the Parallel Programming Laboratory at the University of Illinois. It was first introduced in the mid-1990s as a tool to simplify the development of complex, large-scale scientific simulations. Charm++ is built on top of C++, enhancing it with features for parallel processing, such as migratable objects and adaptive runtime systems. The language is renowned for its ability to automatically balance computational loads, improving efficiency in high-performance computing environments. Its unique approach to parallelism has made it a valuable tool in fields like molecular dynamics, cosmology, and material science.

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

First 20 minutes

General Charm++. app knowledge and experience

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

What are the key features of Charm++?
Charm++ has several key features including message-driven execution, adaptive runtime system, parallel composition, and migratability of objects.
How would you describe the Adaptive MPI (AMPI) in Charm++?
AMPI is an advanced MPI implementation that supports features such as migratability, over-decomposition, and dynamic load balancing.
What is the role of chare in Charm++?
Chare is the basic unit of parallelism in Charm++. It is a C++ object that can be invoked asynchronously and can migrate across processors.
How would you implement load balancing in Charm++?
Load balancing in Charm++ can be implemented using its runtime system, which automatically measures the load on different processors and migrates objects to balance the load.
What are the advantages of using Charm++ over other parallel programming models?
Charm++ offers several advantages such as dynamic load balancing, over-decomposition, and migratability of objects, which are not available in many other parallel programming models.
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What you’re looking for early on

Does the candidate have a strong understanding of Charm++ and its features?
Has the candidate demonstrated the ability to work with large-scale, distributed systems?
Can the candidate solve complex problems and debug issues effectively?
Does the candidate have experience with other parallel programming models or languages?

Next 20 minutes

Specific Charm++. 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 Charm++ and traditional message-passing models.
The key difference is that Charm++ is message-driven, meaning it does not block on receive operations. It also supports dynamic load balancing and migratability of objects, which are not typically available in traditional message-passing models.
How would you handle communication between chares in Charm++?
Communication between chares in Charm++ is handled using asynchronous method invocations, which are essentially messages sent to methods of chare objects.
What is the purpose of the Charm++ runtime system?
The Charm++ runtime system supports dynamic load balancing, automatic measurement of computational loads, and migration of objects across processors.
How would you use over-decomposition in Charm++?
Over-decomposition can be used in Charm++ to divide the problem into more pieces than there are processors, allowing for more flexibility in load balancing.
What are the challenges in parallel programming that Charm++ addresses?
Charm++ addresses challenges such as load balancing, communication overhead, and latency hiding in parallel programming.
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The ideal back-end app developer

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

At this point, a skilled Charm++. engineer should demonstrate strong problem-solving abilities, proficiency in Charm++. 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 Charm++..

What does this simple Charm++ code do?
module hello {
  mainchare Main {
    entry Main(CkArgMsg* m) {
      CkPrintf("Hello, Charm++ World!\n");
This code defines a Charm++ module named 'hello'. Inside this module, a mainchare named 'Main' is defined. The 'Main' mainchare has an entry method that takes a 'CkArgMsg' pointer as an argument. This method prints 'Hello, Charm++ World!' to the console and then exits the program.
What will be the output of this Charm++ code?
module test {
  mainchare Main {
    entry Main(CkArgMsg* m) {
      CkPrintf("%d\n", m->argc);
This code will print the number of command-line arguments passed to the program. The 'argc' member of the 'CkArgMsg' structure contains this count.
What does this Charm++ code do with the array?
module arrayTest {
  array [1D] A {
    entry void sayHello() {
      CkPrintf("Hello from element %d\n", thisIndex);
This code defines a 1D array named 'A'. Each element of the array has an entry method 'sayHello' that prints a message to the console. The message includes the index of the element in the array.
What does this Charm++ code do related to threading?
module threadTest {
  mainchare Main {
    entry Main(CkArgMsg* m) {
      CkPrintf("Running on %d processors\n", CkNumPes());
This code prints the number of processors available to the program. The 'CkNumPes' function returns this count. This is related to threading because Charm++ uses multiple processors for parallel execution.

Wrap-up questions

Final candidate for Charm++. 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 Charm++. application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

Describe the difference between chares and groups in Charm++.
Chares are individual objects that can migrate across processors, while groups are collections of objects that are fixed to processors.
How would you implement fault tolerance in Charm++?
Fault tolerance in Charm++ can be implemented using its checkpoint/restart mechanism, which allows for the saving and restoring of program states.
What are the key components of Charm++'s adaptive runtime system?
The key components of Charm++'s adaptive runtime system include the measurement module, the load balancing framework, and the migration mechanism.

Charm++. application related

Product Perfect's Charm++. development capabilities

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