SIGEVENT(3)

🦋 SIGEVENT(3) — asynchronous event notification, from the Library Functions Manual 🦋

✨ NAME ✨

sigevent — asynchronous event notification. that's the name, bestie, and it's iconic. 💅

🌈 SYNOPSIS 🌈

the one include you need:

#include <signal.h>

💖 DESCRIPTION 💖

okay so some operations permit threads to request asynchronous notification of events via a struct sigevent structure. this structure contains several fields that describe the requested notification — and the way that this struct lays out its fields? obsessed. no cap, every single one matters:

• int sigev_notify — notification method
• int sigev_signo — signal number
• union sigval sigev_value — signal value
• int sigev_notify_kqueue — kqueue(2) file descriptor
• unsigned short sigev_notify_kevent_flags — kevent flags
• lwpid_t sigev_notify_thread_id — LWP ID
• void (*)(union sigval) sigev_notify_function — callback function pointer
• pthread_attr_t * sigev_notify_attributes — callback thread attributes

the sigev_notify field specifies the notification method used when the event triggers: lowkey choose your fighter 🎀

• SIGEV_NONE — no notification is sent. literally ghost mode, not me sending nothing. 👻
• SIGEV_SIGNAL — the signal sigev_signo is queued as a real-time signal to the calling process. the value stored in sigev_value will be present in the si_value of the siginfo_t structure of the queued signal. signal delivery said hi. 📬
• SIGEV_THREAD — the notification function in sigev_notify_function is called in a separate thread context. the thread is created with the attributes specified in *sigev_notify_attributes. the value stored in sigev_value is passed as the sole argument to sigev_notify_function. if sigev_notify_attributes is NULL, the thread is created with default attributes. thread behavior, slay. 🧵
• SIGEV_KEVENT — a new kevent is posted to the kqueue sigev_notify_kqueue. the udata member of the kevent structure contains the value stored in sigev_value. the meaning of other fields in the kevent are specific to the type of triggered event. kqueue girlies rise. 🌊
• SIGEV_THREAD_ID — the signal sigev_signo is queued to the thread whose LWP ID is sigev_notify_thread_id. the value stored in sigev_value will be present in the si_value of the siginfo_t structure of the queued signal. specific-thread delivery, periodt. 🎯

🚨 NOTES 🚨

note note note: programs wishing to use SIGEV_THREAD notifications must link against the POSIX Real-time Library (librt, -lrt). do not forget the link, bestie — iykyk. 😭

🔗 SEE ALSO 🔗

go peek at aio_read(2), mq_notify(2), timer_create(2), and siginfo(3). the whole friend group. 🫶

📜 STANDARDS 📜

the struct sigevent type conforms to IEEE Std 1003.1-2004 (“POSIX.1”). standardized and stunning. ✨

🦋 HISTORY 🦋

the sigevent structure first appeared in FreeBSD 3.3. that's the origin story, fr fr. 💜

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💖 and that's the page, bestie — it's from Debian, dated February 25, 2020, and it's the SIGEVENT(3) page. mwah! 🎀