My Java app sometimes completely freezes without exceptions or logs. I suspect two threads are blocking each other. How should I debug and fix this?

My Java application crashes with NullPointerException in unexpected cases—even after supposedly initializing objects. What causes these NPEs and how do I prevent them?

My Java application occasionally hangs or throws OutOfMemoryError when multiple threads update a shared HashMap. I can’t reliably reproduce it and debugging is difficult. What might be happening?

In a heavily concurrent application using HashMap, the program sometimes crashes with OutOfMemoryError, or iteration behaves incorrectly. What’s causing it, and how do I fix it?

In my multi-threaded application, a thread sleeping inside a loop gets interrupted, but the interrupt flag is ignored or swallowed. The thread doesn’t stop and continues looping—leading to runaway execution or resource leaks. What’s wrong, and how sh...

I implemented a singleton pattern using double checked locking without declaring the instance variable as volatile. In multithreaded environments, occasionally two threads create separate instances or one receives an incompletely initialized object....

Using virtual threads heavily in Java 19, my application gradually consumes native memory and freezes, even though thread counts are low. What’s happening?

When evolving a Java class, I occasionally encounter InvalidClassException or unexpected behavior after deserializing older serialized objects. What’s causing this and how do I correct it?

I have a Java class that overrides finalize() for cleanup. Under high object allocation rates, the JVM becomes slow or crashes with OutOfMemoryError. Why is this happening and how should I fix it?

In a React useEffect, I call an async function but forget to await or return it. If it throws, I get an unlogged rejection or erratic component behavior.

Functions with infinite recursion crash with “Maximum call stack exceeded,” but infinite loops using while(true) just hang/crash without stack errors. Why?

My debounced function isn’t acting on the latest input or has undefined variables—especially when the handler needs access to current input values.

Implementing autocomplete: users type fast, sending multiple fetch calls. Sometimes, results from an earlier request replace the newer ones, causing wrong suggestions to display.

Why doesn’t this wait, and how do I correctly handle async logic in loops?

My Node.js app launches multiple shell commands via child_process.spawn() in parallel. It's slow, causes spikes in memory and CPU, and sometimes crashes. What alternatives can help avoid these slowdowns?

Some APIs in my Node.js/Express app respond slowly occasionally—responses take several seconds even though CPU & memory usage look normal and DB calls are fast. Distributing load across PM2 cluster doesn't help. What might be causing this slowdown?

When processing a large number of files (e.g. reading or watching directories with thousands of files), Node.js throws: arduino Copy code Error: EMFILE: too many open files Even though .readFile() or .watch() is used, the process crashes. How can...

My Node.js service consumes more memory over time—even without increased load—and eventually crashes with heap out of memory. What's likely causing this leak?

I configured a custom Undici Agent with very large timeouts (e.g. headersTimeout: 3,000,000), but long-running fetch calls still fail after several minutes with TypeError: fetch failed caused by HeadersTimeoutError.

When using built-in fetch() in Node.js (v18+), requests occasionally fail with: php Copy code TypeError: fetch failed cause: ConnectTimeoutError (code: 'UND_ERR_CONNECT_TIMEOUT') Even using AbortSignal.timeout(…) set to a high value (e.g. 20 s)...