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Modify

前置阅读

sub.Modify(...)​

修改 Subscription 的发布参数 (ModifySubscription 服务):

ModifySubscriptionResult Modify(
    double publishing_interval_ms,
    uint32_t lifetime_count                = 1200,
    uint32_t max_keep_alive_count          = 50,
    uint32_t max_notifications_per_publish = 0,
    uint8_t  priority                      = 0);
参数含义
publishing_interval_ms新发布间隔
lifetime_count多少个 publish 周期没收到 PublishRequest 就清理订阅
max_keep_alive_count没新数据时多久发一次空 KeepAlive
max_notifications_per_publish单次 Publish 最多发多少条通知, 0 = 不限
priority优先级

返回 ModifySubscriptionResult:

struct ModifySubscriptionResult {
    double   revised_publishing_interval_ms = 0.0;
    uint32_t revised_lifetime_count         = 0;
    uint32_t revised_max_keep_alive_count   = 0;
};
auto rev = sub.Modify(/*publishing_interval_ms=*/1000.0,
                      /*lifetime_count=*/600,
                      /*max_keep_alive_count=*/30);
std::cout << "Revised publishing interval = "
          << rev.revised_publishing_interval_ms << " ms\n";

sub.ModifyMonitoredItems(requests)​

批量修改 MI 采样参数 (ModifyMonitoredItems 服务):

std::vector<ModifyMonitoredItemResult> ModifyMonitoredItems(
    std::vector<MonitoredItemModifyRequest> const& requests);

MonitoredItemModifyRequest 字段:

struct MonitoredItemModifyRequest {
    uint32_t monitored_item_handle = 0;
    double   sampling_interval_ms  = -1.0;   // -1 = 跟订阅, 0 = 尽快
    uint32_t queue_size            = 1;
    bool     discard_oldest        = true;
};

返回 ModifyMonitoredItemResult:

struct ModifyMonitoredItemResult {
    Status   status                       = Status::Bad;
    double   revised_sampling_interval_ms = 0.0;
    uint32_t revised_queue_size           = 0;
};
std::vector<MonitoredItemModifyRequest> reqs;
for (auto h : mi_handles) {
    MonitoredItemModifyRequest r;
    r.monitored_item_handle = h;
    r.sampling_interval_ms  = 50.0;
    r.queue_size            = 10;
    r.discard_oldest        = true;
    reqs.push_back(r);
}
auto results = sub.ModifyMonitoredItems(reqs);

sub.ModifyItem(...) 单 MI 简化版​

ModifyMonitoredItemResult ModifyItem(
    uint32_t mi_handle,
    double sampling_interval_ms,
    uint32_t queue_size = 1,
    bool discard_oldest = true);
auto r = sub.ModifyItem(handle, /*sampling_interval_ms=*/50.0);
std::cout << "Revised sampling = " << r.revised_sampling_interval_ms << " ms\n";

QueueSize 与 DiscardOldest​

服务端为每个 MI 维护一个先进先出队列. 当客户端 Publish 来不及取时, 队列满了:

  • discard_oldest = true (默认) → 丢最旧, 保留最新
  • discard_oldest = false → 丢最新, 保留最旧

queue_size = 1 (默认) 只保留最新值, 适合"实时显示"; queue_size = N (N > 1) 适合"采样不能漏"的高频数据.

下一步​