GRPC同步请求设置ClientContext截止时间触发删除构造函数调用错误求助

问题场景 #

为GRPC同步请求配置grpc::ClientContext时，设置deadline的代码触发编译错误，移除Context相关代码后程序可正常运行。

函数代码 #

grpc::Status Connection::syncLookup(Foo::LookupRequest &request, Foo::LookupResponse *response) {
    bool failure = false;
    grpc::ClientContext ctx;

    Clock::time_point now = Clock::now();
    auto time_since_epoch = std::chrono::duration_cast<Ms>(now.time_since_epoch()).count();

    if (rpc_timeout_ms_ > 0)
    {
        Clock::time_point deadline = now + Ms(rpc_timeout_ms_);
        ctx.set_deadline(deadline);
    }
    grpc::Status status = lookup_stub_->Lookup(&ctx, request, response);
    if (!status.ok())
    {
        failure = true;
        stats_worker_.record(time_since_epoch, failure, peerAddress(ctx));
        return status;
    }
    stats_worker_.record(time_since_epoch, failure, response->serverid());
    return status;
}

编译错误信息 #

In file included from ~/.local/include/grpc++/grpc++.h:26:
In file included from ~/.local/include/grpcpp/grpcpp.h:53:
In file included from ~/.local/include/grpcpp/client_context.h:37:
~/.local/include/grpcpp/impl/codegen/client_context.h:275:24: error: call to deleted constructor of 'grpc::TimePoint<time_point<steady_clock, duration<long long, ratio<1, 1000000000>>>>'
    grpc::TimePoint<T> deadline_tp(deadline);
                       ^           ~~~~~~~~
~/dev/cpp/grpc/lookupv2/lookup.cc:104:17: note: in instantiation of function template specialization 'grpc::ClientContext::set_deadline<std::chrono::time_point<std::chrono::steady_clock, std::chrono::duration<long long, std::ratio<1, 1000000000>>>>' requested here
            ctx.set_deadline(deadline);
~/.local/include/grpcpp/impl/codegen/time.h:48:3: note: 'TimePoint' has been explicitly marked deleted here
  TimePoint(const T& /*time*/) = delete;



In file included from ~/.local/include/grpc++/grpc++.h:26:
In file included from ~/.local/include/grpcpp/grpcpp.h:53:
In file included from ~/.local/include/grpcpp/client_context.h:37:
~/.local/include/grpcpp/impl/codegen/client_context.h:276:29: error: attempt to use a deleted function
    deadline_ = deadline_tp.raw_time();
                            ^
~/.local/include/grpcpp/impl/codegen/time.h:49:16: note: 'raw_time' has been explicitly marked deleted here
  gpr_timespec raw_time() = delete;

解决方法 #

原因分析 #

你使用的GRPC版本中，ClientContext::set_deadline的模板实现已移除对直接传入std::chrono::steady_clock类型time_point的支持，内部依赖的grpc::TimePoint构造函数和raw_time方法被显式删除，导致无法完成类型转换。

方案一：改用相对超时（推荐） #

直接使用set_timeout方法设置相对超时时间，无需手动计算deadline，GRPC内部会自动处理当前时间加超时的逻辑：

if (rpc_timeout_ms_ > 0)
{
    ctx.set_timeout(std::chrono::milliseconds(rpc_timeout_ms_));
}

方案二：转换为gpr_timespec类型传入 #

如果必须使用绝对deadline，手动将std::chrono的time_point转换为GRPC原生的gpr_timespec类型，再调用set_deadline的对应重载：

#include <grpcpp/impl/codegen/time.h>

// ...

if (rpc_timeout_ms_ > 0)
{
    Clock::time_point deadline = now + Ms(rpc_timeout_ms_);
    gpr_timespec gpr_deadline = grpc::chrono_steady_clock_to_gpr_time(deadline, GPR_CLOCK_REALTIME);
    ctx.set_deadline(gpr_deadline);
}

注意：如果你的Clock是std::chrono::system_clock，则使用grpc::chrono_system_clock_to_gpr_time函数。

方案三：替换时间类型为system_clock #

部分GRPC版本仅支持std::chrono::system_clock的time_point传入set_deadline，可以修改Clock的定义：

using Clock = std::chrono::system_clock;

内容的提问来源于stack exchange，提问作者amlwwalker