[coll] Add C API for the tracker. (#9773)

tests/cpp/collective/test_coll_c_api.cc

@@ -0,0 +1,63 @@
+/**
+ * Copyright 2023, XGBoost Contributors
+ */
+#include <gtest/gtest.h>
+#include <xgboost/c_api.h>
+
+#include <chrono>  // for ""s
+#include <thread>  // for thread
+
+#include "../../../src/collective/tracker.h"
+#include "test_worker.h"   // for SocketTest
+#include "xgboost/json.h"  // for Json
+
+namespace xgboost::collective {
+namespace {
+class TrackerAPITest : public SocketTest {};
+}  // namespace
+
+TEST_F(TrackerAPITest, CAPI) {
+  TrackerHandle handle;
+  Json config{Object{}};
+  config["dmlc_communicator"] = String{"rabit"};
+  config["n_workers"] = 2;
+  config["timeout"] = 1;
+  auto config_str = Json::Dump(config);
+  auto rc = XGTrackerCreate(config_str.c_str(), &handle);
+  ASSERT_EQ(rc, 0);
+  rc = XGTrackerRun(handle);
+  ASSERT_EQ(rc, 0);
+
+  std::thread bg_wait{[&] {
+    Json config{Object{}};
+    auto config_str = Json::Dump(config);
+    auto rc = XGTrackerWait(handle, config_str.c_str());
+    ASSERT_EQ(rc, 0);
+  }};
+
+  char const* cargs;
+  rc = XGTrackerWorkerArgs(handle, &cargs);
+  ASSERT_EQ(rc, 0);
+  auto args = Json::Load(StringView{cargs});
+
+  std::string host;
+  ASSERT_TRUE(GetHostAddress(&host).OK());
+  ASSERT_EQ(host, get<String const>(args["DMLC_TRACKER_URI"]));
+  auto port = get<Integer const>(args["DMLC_TRACKER_PORT"]);
+  ASSERT_NE(port, 0);
+
+  std::vector<std::thread> workers;
+  using namespace std::chrono_literals;  // NOLINT
+  for (std::int32_t r = 0; r < 2; ++r) {
+    workers.emplace_back([=] { WorkerForTest w{host, static_cast<std::int32_t>(port), 1s, 2, r}; });
+  }
+  for (auto& w : workers) {
+    w.join();
+  }
+
+  rc = XGTrackerFree(handle);
+  ASSERT_EQ(rc, 0);
+
+  bg_wait.join();
+}
+}  // namespace xgboost::collective