[coll] Implement a new tracker and a communicator. (#9650)

* [coll] Implement a new tracker and a communicator.

The new tracker and communicators communicate through the use of JSON documents. Along
with which, communicators are aware of each other.

tests/cpp/collective/test_tracker.cc

@@ -1,18 +1,67 @@
 /**
  * Copyright 2023, XGBoost Contributors
  */
-#include "../../../src/collective/tracker.h"  // for GetHostAddress
-#include "net_test.h"                         // for SocketTest
+#include <gtest/gtest.h>
+
+#include <chrono>   // for seconds
+#include <cstdint>  // for int32_t
+#include <string>   // for string
+#include <thread>   // for thread
+#include <vector>   // for vector
+
+#include "../../../src/collective/comm.h"
+#include "test_worker.h"
 
 namespace xgboost::collective {
 namespace {
-class TrackerTest : public SocketTest {};
+class PrintWorker : public WorkerForTest {
+ public:
+  using WorkerForTest::WorkerForTest;
+
+  void Print() {
+    auto rc = comm_.LogTracker("ack:" + std::to_string(this->comm_.Rank()));
+    ASSERT_TRUE(rc.OK()) << rc.Report();
+  }
+};
 }  // namespace
 
-TEST_F(TrackerTest, GetHostAddress) {
-  std::string host;
-  auto rc = GetHostAddress(&host);
-  ASSERT_TRUE(rc.OK());
-  ASSERT_TRUE(host.find("127.") == std::string::npos);
+TEST_F(TrackerTest, Bootstrap) {
+  RabitTracker tracker{host, n_workers, 0, timeout};
+  auto fut = tracker.Run();
+
+  std::vector<std::thread> workers;
+  std::int32_t port = tracker.Port();
+
+  for (std::int32_t i = 0; i < n_workers; ++i) {
+    workers.emplace_back([=] { WorkerForTest worker{host, port, timeout, n_workers, i}; });
+  }
+  for (auto &w : workers) {
+    w.join();
+  }
+
+  ASSERT_TRUE(fut.get().OK());
 }
+
+TEST_F(TrackerTest, Print) {
+  RabitTracker tracker{host, n_workers, 0, timeout};
+  auto fut = tracker.Run();
+
+  std::vector<std::thread> workers;
+  std::int32_t port = tracker.Port();
+
+  for (std::int32_t i = 0; i < n_workers; ++i) {
+    workers.emplace_back([=] {
+      PrintWorker worker{host, port, timeout, n_workers, i};
+      worker.Print();
+    });
+  }
+
+  for (auto &w : workers) {
+    w.join();
+  }
+
+  ASSERT_TRUE(fut.get().OK());
+}
+
+TEST_F(TrackerTest, GetHostAddress) { ASSERT_TRUE(host.find("127.") == std::string::npos); }
 }  // namespace xgboost::collective