Advanced · Module 6 · Lesson 4 of 10

Signal Masks, Pending Signals, and Async-Signal Safety

Block and unblock signals using sigset_t bitmasks, trace signal coalescence in pending bitmaps, eliminate pause race conditions with sigsuspend, and guarantee async-signal safety.

ProAbout 16 minutes

By the end you can

Manipulate signal sets using sigemptyset, sigfillset, sigaddset, and sigdelset
Protect critical sections against interruption using sigprocmask
Differentiate non-queued standard POSIX signals from real-time queued signals
Identify async-signal-safe library functions and eliminate allocator deadlocks

Builds on Signal Architecture and Delivery with sigaction.

01 · A question first

Why does calling printf() or malloc() inside a signal handler work during quick testing, yet intermittently deadlocks your production server under high load? The answer lies in reentrancy, global heap locks, and POSIX async-signal safety.

Make a guess before you read on.

02 · The idea

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What's inside

Start with the problem
How the idea works
Why it is correct
What it costs
Pitfalls and variations
Where it is used