[metadata]
id = "CON03-C"
type = "recommendation"
category = "CON"
number = 3
title = "Ensure visibility when accessing shared variables"
description = """
Reading a shared primitive variable in one thread may not yield the value of the
most recent write to the variable from another thread. Consequently, the thread
may observe a stale value of the shared variable. To ensure the visibility of
the most recent update, the write to the variable musthappen beforethe read (C
Standard, subclause 5.1.2.4, paragraph 18 [ISO/IEC 9899:2011]). Atomic
operations—other than relaxed atomic operations—trivially satisfy the happens
before relationship. Where atomic operations are inappropriate, protecting both
reads and writes with a mutex also satisfies the happens before relationship.
This noncompliant code example uses ashutdown()method to set the non-
volatiledoneflag that is checked in therun()method. final class ControlledStop
implements Runnable { private boolean done = false; @Override public void run()
{ while (!done) { try { // ... Thread.currentThread().sleep(1000); // Do
something } catch(InterruptedException ie) { Thread.currentThread().interrupt();
// Reset interrupted status } } } public void shutdown() { done = true; } }
"""
severity = "Medium"
likelihood = "Probable"
priority = "P4"
level = "L3"
cert_version = "2016 Edition (Wiki)"
last_modified = "Jul 24, 2025"
[rules.cert_c.CON03-C]
enabled = true
[references]
wiki = "https://wiki.sei.cmu.edu/confluence/display/c/CON03-C.+Ensure+visibility+when+accessing+shared+variables"