signalfd Consumes Blocked Signals Through File Descriptor Reads

Wed, 23 Sep 2026 00:00:00 +0000

signalfd Consumes Blocked Signals Through File Descriptor Reads

signalfd() turns selected signal notifications into records that can be consumed with read(). A matching pending signal makes the descriptor readable, which allows signal handling to share the same poll(), select(), or epoll path as sockets, timers, and other descriptors.

The descriptor does not redirect signals merely because its mask names them. Normal signal-mask rules still apply. In the usual design, the selected signals are blocked before they can be delivered through their ordinary dispositions, then a signalfd reads the pending instances.

signalfd Turns Blocked Signals into Readable Events

Tue, 22 Sep 2026 00:00:00 +0000

Linux signals normally interrupt a thread through asynchronous delivery. signalfd() offers a different boundary for selected signals: keep them blocked in the relevant threads, then consume pending instances by reading a file descriptor.

The signal mechanism itself does not become a byte stream. The kernel still maintains signal state and normal process- or thread-directed delivery rules. signalfd adds a file-descriptor interface for accepting signals from a configured set.

Blocking and the descriptor mask are separate state

A signalfd has a signal-set mask that selects which signals it can accept. That mask does not block those signals for a thread. Normal use therefore pairs descriptor creation with a signal mask operation.

Signalfd on Nalar

signalfd Consumes Blocked Signals Through File Descriptor Reads

signalfd Consumes Blocked Signals Through File Descriptor Reads

signalfd Turns Blocked Signals into Readable Events

Blocking and the descriptor mask are separate state