XtAppAddSignal(3)

💖 XtAppAddSignal — bestie edition 💖

okay so this is XtAppAddSignal(3), and it lives in the XT FUNCTIONS fam (the X Toolkit Intrinsics crowd, you know the vibe 🫶). it's the trio of functions that let you register, remove, and notice a signal source. signal handling but make it Intrinsics-flavored. iconic honestly.

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✨ NAME ✨

XtAppAddSignal, XtRemoveSignal, XtNoticeSignal — register and remove a signal source 💅

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🌸 SYNTAX 🌸

#include <X11/Intrinsic.h>

XtSignalId XtAppAddSignal(XtAppContext app_context, XtSignalCallbackProc
       proc, XtPointer client_data);

void XtRemoveSignal(XtSignalId id);

void XtNoticeSignal(XtSignalId id);

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🎀 ARGUMENTS 🎀

• app_context — specifies the application context. the whole vibe container, basically.
• client_data — specifies the argument that is to be passed to the specified procedure when a signal has been raised. it's the little gift bag 🎁 you hand over to proc.
• id — specifies the ID returned from the corresponding XtAppAddSignal call. yes bestie, you have to keep it. it's your receipt 🧾.
• proc — specifies the procedure that is to be called when the signal has been raised. the main character of the callback moment ✨.

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🦋 DESCRIPTION 🦋

XtAppAddSignal kicks off a mechanism for handling signals within the context of the Intrinsics. the way this works: before you go and establish an operating-system-dependent signal handler, your app can call XtAppAddSignal and stash the returned id somewhere the signal handler can actually reach it. no cap, that part matters — the handler needs to find that id later.

then, when the operating system sends you a signal (rude of it, but okay), the application may call XtNoticeSignal passing the id that XtAppAddSignal gave back. that's the whole handshake 🫱.

⚠️ the big one: XtNoticeSignal is the only Intrinsics function that can safely be called from a signal handler. like, the only one. do not be out here calling other Intrinsics stuff in your handler, bestie, that's not it.

and here's the cute little detail: if XtNoticeSignal gets called multiple times before the Intrinsics are able to invoke the registered callback, the callback is only called once. one and done. logically, the Intrinsics keep a "pending" flag for each registered callback. that flag starts out False, and XtNoticeSignal sets it to True. the Intrinsics invoke the callback whenever the flag is True — and right before the callback is invoked, the flag gets flipped back to False. so it's giving "noted 💅, I'll deal with it once."

XtRemoveSignal is what you call to remove the specified Intrinsics signal handler. and listen — the client should disable the source of the signal before calling XtRemoveSignal. like, turn the tap off before you take the sink out. lowkey important.

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🌈 SEE ALSO 🌈

• XtAppAddTimeOut(3),XtAppAddInput(3),XtAppAddWorkProc(3)
• X Toolkit Intrinsics - C Language Interface
• Xlib - C Language Interface

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and that's the page, bestie 🥰 it's from X Version 11, libXt 1.3.1 — go forth and handle your signals safely, ily, mwah 💖🧚✨