Explicit GC Call

ID

kotlin.explicit_gc_call

Severity

low

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Code Smell

Language

Kotlin

Tags

best-practice, performance

Description

Reports explicit calls to System.gc() or Runtime.getRuntime().gc(). Invoking the garbage collector from application code disrupts the JVM’s autonomous scheduling and almost always produces the opposite of the intended effect.

Rationale

Modern JVM garbage collectors (G1, ZGC, Shenandoah) are highly adaptive. They schedule collection based on heap pressure, allocation rates, and pause-time goals. An explicit System.gc() call can trigger a full GC at the worst possible moment, causing a significant pause, inflating latency measurements, and interfering with the collector’s internal heuristics. In some JVM configurations the call is silently ignored anyway.

// Bad
fun cleanup() {
    System.gc()
    Runtime.getRuntime().gc()
}

// Good — tune the JVM instead
// -XX:+UseG1GC -Xmx2g

Remediation

Remove the explicit GC call. If memory pressure is a concern, address the root cause: fix memory leaks, reduce allocation rate, or tune JVM heap flags. If the call exists as a testing aid, gate it behind a system property or test-only code path.

References