while condition whose variables are never updated in the body
ID |
rust.correctness.while_immutable_condition |
Severity |
low |
Remediation Complexity |
medium |
Remediation Risk |
low |
Remediation Effort |
low |
Resource |
Control Flow |
Language |
Rust |
Description
Reports a while loop whose condition compares two simple variables and whose body never assigns to either of them, never borrows one mutably, and never leaves the loop with break or return. Such a loop spins forever.
Rationale
The condition is re-evaluated on every iteration, but nothing in the body can change its outcome, so the loop either never runs or never ends. In a release build the thread hangs while consuming a core; in a service it holds whatever locks and connections it acquired before entering the loop, so the failure spreads well beyond the spinning thread and is hard to attribute back to this code.
The following code illustrates the pattern detected by this rule:
fn current_usage() -> usize { 0 }
fn wait_for_capacity(limit: usize) {
let used = current_usage();
// FLAGGED: while condition whose variables are never updated in the body
while used < limit {
std::thread::sleep(std::time::Duration::from_millis(10));
}
}Remediation
Update the loop variable in the body (i += 1), recompute the value the condition reads from, or exit explicitly with break when the terminating event occurs. When the loop waits on another thread, use a channel, Condvar or an atomic with acquire/release ordering rather than re-reading a plain local.