76 lines
2.3 KiB
C++
76 lines
2.3 KiB
C++
// Example 15 — Per-node Error Handler
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//
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// Demonstrates set_error_handler() for deciding whether a network can
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// continue when a node throws an exception.
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//
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// The "validator" node rejects even numbers by throwing std::runtime_error.
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// Its error handler logs the failure and returns true (skip & continue),
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// so odd numbers still flow through to the sink.
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//
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// Compare: a second handler (commented below) returns false instead,
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// which stops the node and gracefully shuts the downstream side down.
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//
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// Pipeline: [source] --int--> [validator] --int--> [sink]
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#include <kpn/kpn.hpp>
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#include <chrono>
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#include <iostream>
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#include <thread>
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static int counter = 0;
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static int source() {
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std::this_thread::sleep_for(std::chrono::milliseconds(20));
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return ++counter;
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}
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static int validate(int x) {
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if (x % 2 == 0)
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throw std::runtime_error("even number rejected: " + std::to_string(x));
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return x;
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}
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static int received = 0;
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static void sink(int x) {
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std::cout << " processed: " << x << '\n';
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++received;
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}
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int main() {
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using namespace kpn;
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auto src = make_node<source> ();
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auto proc = make_node<validate>();
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auto snk = make_node<sink> ();
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// --8<-- [start:error_handler]
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// Return true → skip this invocation, keep the node running.
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// Return false → stop the node (downstream drains then also stops).
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proc.set_error_handler([](std::string_view name, std::exception_ptr ep) {
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try { std::rethrow_exception(ep); }
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catch (const std::exception& e) {
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std::cerr << "[" << name << "] skipping item — " << e.what() << '\n';
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}
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return true;
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});
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// --8<-- [end:error_handler]
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Network net;
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net.add("source", src)
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.add("validator", proc)
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.add("sink", snk)
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.connect("source", src.output<0>(), "validator", proc.input<0>())
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.connect("validator", proc.output<0>(), "sink", snk.input<0>())
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.build();
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std::cout << "source emits 1..N; validator rejects even numbers.\n"
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<< "Error messages on stderr, accepted items on stdout.\n\n";
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net.start();
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std::this_thread::sleep_for(std::chrono::milliseconds(300));
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net.stop();
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std::cout << "\nItems accepted by sink: " << received << '\n';
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}
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