Q: How do you write unit tests and benchmark tests in Go?

Write tests in files named `_test.go` using the `testing` package. Unit tests use `func TestX(t *testing.T)`. Benchmark tests use `func BenchmarkX(b *testing.B)` containing loops running `b.N` times to measure durations.

Q: Explain panic, recover, and defer in Go exception handling.

`panic` stops normal execution, unwinding the stack and running deferred functions. A deferred function can call `recover()` to capture the panic object and resume execution, preventing process crashes.

Q: What is the Go Garbage Collector and how does it optimize collections?

Go uses a concurrent, tri-color mark-and-sweep garbage collector. It runs concurrently with goroutines, minimizing 'Stop the World' (STW) pauses to sub-millisecond durations.

Q: How do you detect memory leaks and profile Go code using pprof?

Import `net/http/pprof` to expose profiling endpoints. Run load tests, capture heap profiles using `go tool pprof`, and inspect allocations to identify leaking memory.

Q: What is the difference between passing by value and passing by pointer in Go?

Passing by value copies parameter bytes onto the stack. Passing by pointer passes memory addresses, letting functions modify original values, but risking escaping allocations to the heap.

Q: How do you mock interfaces in Go testing?

Define mock structs implementing the target interface. In tests, pass the mock struct instance containing stubbed method variables to isolate your code from database or API services.

Q: Explain Go's init() function and its initialization order.

The `init()` function runs once per package at startup, after package variables are initialized. If multiple packages import each other, Go resolves imports in order, running `init` functions sequentially.

Question 1

Explain Go's M:N scheduler (GMP model) and how it coordinates concurrency.

Accepted Answer

Go's runtime schedules Goroutines (`G`) onto Logical Processors (`P`), which map to OS Threads (`M`). The scheduler uses a work-stealing algorithm: if a thread `M` runs out of goroutines, it steals work from other threads' run queues, maximizing CPU cores.

Question 2

Explain Go Mutexes (sync.Mutex and sync.RWMutex) and when to use each.

Accepted Answer

- `sync.Mutex` blocks all access to a critical resource, allowing only one goroutine lock at a time.
- `sync.RWMutex` allows multiple concurrent readers but only one writer, which is optimal for read-heavy state caches.

Question 3

How do you handle timeouts in Go concurrency using context?

Accepted Answer

Create a context with a timeout: `ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)`. Pass this context to APIs and check for cancellation inside select blocks: `case <-ctx.Done():`.

Question 4

How do you write unit tests and benchmark tests in Go?

Accepted Answer

Write tests in files named `_test.go` using the `testing` package. Unit tests use `func TestX(t *testing.T)`. Benchmark tests use `func BenchmarkX(b *testing.B)` containing loops running `b.N` times to measure durations.

Question 5

Explain panic, recover, and defer in Go exception handling.

Accepted Answer

`panic` stops normal execution, unwinding the stack and running deferred functions. A deferred function can call `recover()` to capture the panic object and resume execution, preventing process crashes.

Question 6

What is the Go Garbage Collector and how does it optimize collections?

Accepted Answer

Go uses a concurrent, tri-color mark-and-sweep garbage collector. It runs concurrently with goroutines, minimizing 'Stop the World' (STW) pauses to sub-millisecond durations.

Question 7

How do you detect memory leaks and profile Go code using pprof?

Accepted Answer

Import `net/http/pprof` to expose profiling endpoints. Run load tests, capture heap profiles using `go tool pprof`, and inspect allocations to identify leaking memory.

Question 8

What is the difference between passing by value and passing by pointer in Go?

Accepted Answer

Passing by value copies parameter bytes onto the stack. Passing by pointer passes memory addresses, letting functions modify original values, but risking escaping allocations to the heap.

Question 9

How do you mock interfaces in Go testing?

Accepted Answer

Define mock structs implementing the target interface. In tests, pass the mock struct instance containing stubbed method variables to isolate your code from database or API services.

Question 10

Explain Go's init() function and its initialization order.

Accepted Answer

The `init()` function runs once per package at startup, after package variables are initialized. If multiple packages import each other, Go resolves imports in order, running `init` functions sequentially.

Question 11

Explain how to write custom middlewares in Go HTTP servers.

Accepted Answer

Write a function that takes a `http.Handler` and returns another handler. Intercept requests, execute middleware logic, and call the next handler's `ServeHTTP` method to pass execution.

Question 12

What is the difference between sync.WaitGroup and channels for synchronization?

Accepted Answer

- `sync.WaitGroup` is a simple counter used to wait for a set of goroutines to complete.
- Channels share data and coordinates tasks dynamically, which is more powerful for pipelining.

Question 13

How do you handle JSON serialization and deserialization in Go?

Accepted Answer

Use the `encoding/json` package. Define structs with JSON tags: `type User struct { Name string `json:"name"` }`. Marshal structs into JSON bytes or unmarshal bytes back into structs.

Question 14

Explain Go struct tags and how they are parsed using reflection.

Accepted Answer

Struct tags are string annotations attached to fields. Go modules (like JSON parsers or ORMs) parse these annotations at runtime using the `reflect` package to map fields to keys.

Question 15

How do you prevent goroutine leaks in Go applications?

Accepted Answer

Ensure that goroutines spawned to handle tasks (like reading channels) have exit conditions. If a channel is never closed or read, the goroutine blocks indefinitely, causing leaks.

Question 16

How do you write integration tests that access local Docker databases?

Accepted Answer

Use test libraries (like `testcontainers-go`) to spin up temporary database containers inside your test setup hooks, running migrations and tearing down resources after tests complete.

Question 17

Explain Go Memory Allocations (Stack vs Heap, Escape Analysis) and how to write allocations-free code.

Accepted Answer

Go allocates variables either on the Stack or the Heap:
- Stack: Fast allocation and deallocation linked to function lifecycles, with zero GC overhead.
- Heap: Slow allocation managed by the GC.

Go uses Escape Analysis at compile time to determine if a variable escapes to the heap (e.g. returning a pointer to a local variable). To write allocation-free code:
1. Run escape analysis: Build code using `go build -gcflags="-m"` to see escape logs.
2. Avoid pointer indicators on small structs: Copying small structs on the stack is faster than heap allocation.
3. Reuse memory: Use `sync.Pool` to reuse buffers and slices, reducing allocations under load.

Question 18

How do you optimize Go HTTP servers for high-throughput API services (50k+ QPS)?

Accepted Answer

To optimize Go servers for high QPS:
1. Keep allocations zero: Reuse request/response buffers and JSON decoders.
2. Connection pooling: Configure keep-alive limits, idle connection pools, and timeouts on database and HTTP client drivers.
3. Avoid GC spikes: Configure `GOGC` or `GOMEMLIMIT` environment variables to control GC frequencies, preventing CPU spikes from GC sweeps.

Question 19

Explain distributed context propagation inside Go microservices architectures.

Accepted Answer

Context propagation involves passing trace and span IDs across network boundaries. Inject trace headers into outgoing HTTP client requests, and write middleware on receiving servers to extract headers and load them into the request `context.Context`.

Question 20

Explain Go security best practices: protecting against race conditions and dependency vulnerabilities.

Accepted Answer

Secure Go applications by:
1. Race Detector: Compile and test code using the race detector: `go test -race ./...` to locate concurrent state access violations.
2. Dependency audits: Run `go govulncheck ./...` in CI/CD pipelines to scan dependencies for known vulnerabilities, keeping module packages updated.

Question 21

How would you implement a distributed worker pool in Go using channels?

Accepted Answer

Create a central dispatcher that coordinates worker goroutines. Workers read tasks from a shared channel. Scale by configuring buffer capacities on channels and spawning workers dynamically based on CPU core counts.

Question 22

Explain how to write custom reflect type mappings in Go.

Accepted Answer

Use the `reflect` package to inspect interface types (`reflect.TypeOf`) and values (`reflect.ValueOf`) dynamically. This is useful for writing custom serializers or generic validation engines, though it adds runtime overhead.

Question 23

How do you debug compiler optimization issues in Go?

Accepted Answer

Disable optimizations using compiler flags: `go build -gcflags="-N -l"` to preserve variables and stack traces, making debugging with tools like Delve (`dlv`) accurate.

Question 24

Explain the differences between Go's standard library net/http and fasthttp.

Accepted Answer

- `net/http`: Standard, clean, creates a new goroutine per request, allocating buffers dynamically.
- `fasthttp`: Avoids allocations by using request/response pools, which is faster but has a more complex API.

Question 25

How do you set up distributed session management in Go apps?

Accepted Answer

Store session records in a Redis cluster. Write middleware to query Redis on requests, storing session pointers in `context.Context` to authorize user calls.

Question 26

How do you optimize memory allocations inside Go slices?

Accepted Answer

Pre-allocate slice capacities using `make([]T, 0, capacity)` if the size is known. This avoids dynamic resizing allocations and array copying steps during `append` calls.

Question 27

Explain how Go compiles and links static binaries.

Accepted Answer

Go compiles all code and dependencies into a single, self-contained binary. Disable dynamic links using `CGO_ENABLED=0` to compile static binaries that run inside empty containers (like `scratch`).

Question 28

How do you profile garbage collection latencies in Go?

Accepted Answer

Use environmental variables: `GODEBUG=gctrace=1`. This prints garbage collection durations, memory reclamation sizes, and processor cycles directly to stdout for analysis.

Question 29

Explain how Go interface assertions function at runtime.

Accepted Answer

Interfaces are represented internally as `iface` (interfaces with methods) or `eface` (empty interfaces), storing type pointers and value pointers. Asserts check type pointers dynamically, throwing panics if mismatched.

Question 30

How do you implement secure rate-limiting using token buckets in Go?

Accepted Answer

Use libraries like `golang.org/x/time/rate`. Define a rate limiter specifying capacity and refill rates. Check limits on incoming requests: `limiter.Allow()`, blocking calls if empty.

Question 31

How do you build a custom router engine using Radix tree matching in Go?

Accepted Answer

Implement a Radix tree data structure where each node represents a path segment. Match incoming URL paths against the tree nodes, capturing wildcard parameters dynamically.

Question 32

Explain Go memory allocation arenas.

Accepted Answer

Arenas (`arena` package) allow allocating memory in bulk blocks and freeing the entire block manually at once, bypassing garbage collection scans to optimize performance.

Question 33

How do you debug circular package dependencies in Go?

Accepted Answer

Go forbids circular package imports at compile time. Resolve them by extracting shared interface definitions or variables into a separate, independent sub-package.

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