getter.h File Reference

Read-side primitive of the VLink field communication model. More...

#include <memory>
#include <mutex>
#include <optional>
#include <string>
#include <type_traits>
#include "./base/condition_variable.h"
#include "./base/functional.h"
#include "./impl/getter_impl.h"
#include "./node.h"
#include "./internal/getter-inl.h"

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Classes
class	vlink::Getter< ValueT, SecT >
	Type-safe latest-value reader for the VLink field communication model. More...
class	vlink::SecurityGetter< ValueT >
	Convenience alias of Getter with per-message decryption enabled. More...

Namespaces
	vlink

Detailed Description

Read-side primitive of the VLink field communication model.

Getter<ValueT, SecT> mirrors the latest value produced by a matching Setter on the same URL. Unlike Subscriber it retains only the most recent payload rather than queuing every update, and it offers a blocking wait_for_value() entry point in addition to the standard event callback.

The class is a thin, header-only template wrapper around GetterImpl and owns its own cached value_, change-tracking buffer, and condition variable.

Field-model Data Flow

*   Setter<ValueT>             Transport Back-end             Getter<ValueT>
*   --------------             ------------------             ---------------
*      | set(v)                       |                              |
*      |----------------------------->|  serialised latest value     |
*      |                              |--- overwrites previous ----->|
*      |                              |                              |
*      |                              |                              |  Serializer::
*      |                              |                              |  deserialize
*      |                              |                              |--> listen cb (optional)
*      |                              |                              |--> value_ cached
*      |                              |                              |--> wait_for_value
*      |                              |                              |    returns true
*      |                              |                              |--> get() => value
* 

Getter vs Subscriber

Feature	Getter<T>	Subscriber<T>
Value retention	Latest value cached	None
Transport role tag	kGetter	kSubscriber
Blocking read	wait_for_value()	N/A
Duplicate suppression	set_change_reporting(true)	N/A
Cross-role bridge	mark_as_subscriber()	mark_as_getter()

Read-Mode Variants

Method	Blocking	Result type	Notes
get()	No	std::optional	Returns nullopt initially
wait_for_value(timeout)	Yes	bool (then get())	Default infinite if 0
listen(callback)	No	void(const ValueT&)	Fires on every update
listen(cb) + change_reporting	No	void(const ValueT&)	Suppress identical bytes

Usage Patterns

vlink::Getter<int> g("shm://vehicle/gear");
 
if (auto v = g.get()) { use(*v); }
 
if (g.wait_for_value(std::chrono::milliseconds(500))) {
  use(*g.get());
}
 
g.listen([](const int& v) { on_update(v); });
 
g.set_change_reporting(true);
g.listen([](const int& v) { on_changed(v); });

Note

Until a Setter writes for the first time, get() returns std::nullopt and wait_for_value() blocks.

See also

setter.h, subscriber.h, node.h, serializer.h