getter.h 文件参考

Type-safe field-model reader for VLink topics. 更多...

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

getter.h 的引用(Include)关系图:

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浏览该文件的源代码.

类
class	vlink::Getter< ValueT, SecT >
	Type-safe field reader for the VLink field communication model. 更多...
class	vlink::SecurityGetter< ValueT >
	Convenience alias for Getter with message security enabled. 更多...

命名空间
namespace	vlink

详细描述

Type-safe field-model reader for VLink topics.

Getter<ValueT, SecT> is the read side of the VLink field model. It maintains the latest value published by any matching Setter on the same URL. Unlike Subscriber, it retains only the most recent value rather than queuing a history of updates.

Field Model Overview

Setter<T>                 Transport Back-end              Getter<T>
    |                          |                               |
    |-- set(value) ----------> |                               |
    |   serialize(value)       |-- latest-value delivery ----> |
    |                          |  (overwrites previous)        |--> listen callback(value)
    |                          |                               |    value_ updated
    |                          |                               |--> get() returns latest

Key Differences: Getter vs Subscriber

Feature	Getter<T>	Subscriber<T>
Value retention	Latest value cached	No caching
Transport role	kGetter	kSubscriber
Blocking read	wait_for_value()	N/A
Change-reporting filter	set_change_reporting(true)	No built-in filter
Cross-transport use	As subscriber: mark_as_subscriber()	As getter: mark_as_getter()

Usage Patterns

// Pattern 1: polling
Getter<int> g("shm://my_field");
if (auto v = g.get()) {
    std::cout << "value: " << *v << std::endl;
}
 
// Pattern 2: blocking wait
if (g.wait_for_value()) {
    auto v = g.get();
}
 
// Pattern 3: value-change callback (fires when Setter writes a new value)
g.listen([](const int& v) { std::cout << "updated: " << v << std::endl; });
 
// Pattern 4: change-only reporting (suppress duplicate values)
g.set_change_reporting(true);
g.listen([](const int& v) { ... });

注解

get() and wait_for_value() both require a prior Setter write to return a value. Before any Setter has written, get() returns std::nullopt and wait_for_value() blocks until one does.

模板参数

ValueT	Value type. Must satisfy Serializer::is_supported().
SecT	Security mode; defaults to SecurityType::kWithoutSecurity.