Scheduled Executor With Zero Core Threads

ID

java.executor_zero_core_threads

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

reliability

Description

Reports a java.util.concurrent.ScheduledThreadPoolExecutor whose corePoolSize is set to the literal 0, either as the constructor’s first argument or through a later setCorePoolSize(0) call.

Only the literal 0 is matched; a variable or computed size is not flagged. A plain ThreadPoolExecutor is out of scope — a zero core size there is a legitimate "grow on demand" configuration.

Rationale

A ScheduledThreadPoolExecutor’s pool is sized by `corePoolSize alone, unlike a general ThreadPoolExecutor, which can also grow up to a separate maximum. With corePoolSize at zero, the executor has no threads at all: every task submitted to it is accepted without error and simply never runs.

ScheduledThreadPoolExecutor scheduler = new ScheduledThreadPoolExecutor(0);
scheduler.scheduleAtFixedRate(this::flushBuffer, 0, 5, TimeUnit.SECONDS); // never executes

Remediation

Size the pool with a value greater than zero, chosen for the number of scheduled tasks the application actually runs concurrently:

ScheduledThreadPoolExecutor scheduler = new ScheduledThreadPoolExecutor(4);
scheduler.scheduleAtFixedRate(this::flushBuffer, 0, 5, TimeUnit.SECONDS);

References

© 2026 Xygeni. All rights reserved