[metadata]
id = "CON34-C"
type = "recommendation"
category = "CON"
number = 34
title = "Declare objects shared between threads with appropriate storage durations"
description = """
Accessing the automatic or thread-local variables of one thread from another
thread isimplementation-defined behaviorand can cause invalid memory accesses
because the execution of threads can be interwoven within the constraints of the
synchronization model. As a result, the referenced stack frame or thread-local
variable may no longer be valid when another thread tries to access it. Shared
static variables can be protected by thread synchronization mechanisms. However,
automatic (local) variables cannot be shared in the same manner because the
referenced stack frame's thread would need to stop executing, or some other
mechanism must be employed to ensure that the referenced stack frame is still
valid. Do not access automatic or thread-local objects from a thread other than
the one with which the object is associated. SeeDCL30-C. Declare objects with
appropriate storage durationsfor information on how to declare objects with
appropriate storage durations when data is not being shared between threads.
Noncompliant Code Example (Automatic Storage Duration)
"""
severity = "Medium"
likelihood = "Probable"
priority = "P4"
level = "L3"
cert_version = "2016 Edition (Wiki)"
last_modified = "Oct 31, 2025"
[rules.cert_c.CON34-C]
enabled = true
[references]
wiki = "https://wiki.sei.cmu.edu/confluence/display/c/CON34-C.+Declare+objects+shared+between+threads+with+appropriate+storage+durations"