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doc: Document behavior of non-nullable object arguments in clients

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Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
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Philipp Kerling 2018-01-24 14:28:15 +01:00 • committed by Pekka Paalanen
parent e5b52f673c
commit ef48ff21f0
1 changed files with 13 additions and 2 deletions
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15
src/wayland-util.h
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@ -78,12 +78,23 @@ extern "C" {
* wl_message is to a protocol message like a class is to an object.
*
* The `name` of a wl_message is the name of the corresponding protocol message.
*
* The `signature` is an ordered list of symbols representing the data types
* of message arguments and, optionally, a protocol version and indicators for
* nullability. A leading integer in the `signature` indicates the _since_
* version of the protocol message. A `?` preceding a data type symbol indicates
* that the following argument type is nullable. When no arguments accompany a
* message, `signature` is an empty string.
* that the following argument type is nullable. While it is a protocol violation
* to send messages with non-nullable arguments set to `NULL`, event handlers in
* clients might still get called with non-nullable object arguments set to
* `NULL`. This can happen when the client destroyed the object being used as
* argument on its side and an event referencing that object was sent before the
* server knew about its destruction. As this race cannot be prevented, clients
* should - as a general rule - program their event handlers such that they can
* handle object arguments declared non-nullable being `NULL` gracefully.
*
* When no arguments accompany a message, `signature` is an empty string.
*
* Symbols:
*
* * `i`: int
* * `u`: uint