Timeout with alarm(3) to stop hung C programs on Linux
The post shows how alarm(3) makes the kernel send SIGALRM after an interval, terminating a hung process without a polling loop or watchdog thread. The technique suits tools and tests, provided signal handling is done with care.
By Wendelmaques Pereira · Updated today
Source: Usando alarm(3) para interromper um programa C travado no Linux (x.com). Text prepared with AI from this source.
What happened and what to do
The post explains that calling alarm(3) makes the kernel send a SIGALRM after about three seconds. If the signal's default action is not changed, the process is terminated. This means no polling loop or watchdog thread is needed to bound a runaway section of code.
In practice, a company can use this mechanism as a time limit in internal command-line tools, collection routines and automated tests, where a stuck loop must be cut off without disrupting the rest of the system. The caveat is that the timeout depends on signal handling: it is wise to install a handler that logs the error and exits cleanly, and to check how libraries, threads and blocking calls react to SIGALRM. In data pipelines, combine this limit with failure logging and monitoring so that every cutoff is visible and auditable.
How the consultancy can help
Diagnosis of where C programs or routines run without an execution limit, and implementation of a safe timeout pattern with signal handling, failure logging and tests, operated on the client's infrastructure.
Next step
If your team maintains C tools or pipelines that can hang, send a short description of the case and receive a scoped proposal from Wendelmaques.
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