1 files changed, 124 insertions, 0 deletions
diff --git a/test/syscalls/linux/concurrency.cc b/test/syscalls/linux/concurrency.cc
new file mode 100644
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+++ b/test/syscalls/linux/concurrency.cc
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+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <signal.h>
+#include <atomic>
+
+#include "gtest/gtest.h"
+#include "absl/strings/string_view.h"
+#include "absl/time/clock.h"
+#include "absl/time/time.h"
+#include "test/util/test_util.h"
+#include "test/util/thread_util.h"
+
+namespace gvisor {
+namespace testing {
+namespace {
+
+// Test that a thread that never yields to the OS does not prevent other threads
+// from running.
+TEST(ConcurrencyTest, SingleProcessMultithreaded) {
+  std::atomic<int> a(0);
+
+  ScopedThread t([&a]() {
+    while (!a.load()) {
+    }
+  });
+
+  absl::SleepFor(absl::Seconds(1));
+
+  // We are still able to execute code in this thread. The other hasn't
+  // permanently hung execution in both threads.
+  a.store(1);
+}
+
+// Test that multiple threads in this process continue to execute in parallel,
+// even if an unrelated second process is spawned.
+TEST(ConcurrencyTest, MultiProcessMultithreaded) {
+  // In PID 1, start TIDs 1 and 2, and put both to sleep.
+  //
+  // Start PID 3, which spins for 5 seconds, then exits.
+  //
+  // TIDs 1 and 2 wake and attempt to Activate, which cannot occur until PID 3
+  // exits.
+  //
+  // Both TIDs 1 and 2 should be woken. If they are not both woken, the test
+  // hangs.
+  //
+  // This is all fundamentally racy. If we are failing to wake all threads, the
+  // expectation is that this test becomes flaky, rather than consistently
+  // failing.
+  //
+  // If additional background threads fail to block, we may never schedule the
+  // child, at which point this test effectively becomes
+  // MultiProcessConcurrency. That's not expected to occur.
+
+  std::atomic<int> a(0);
+  ScopedThread t([&a]() {
+    // Block so that PID 3 can execute and we can wait on its exit.
+    absl::SleepFor(absl::Seconds(1));
+    while (!a.load()) {
+    }
+  });
+
+  pid_t child_pid;
+  ASSERT_THAT(child_pid = fork(), SyscallSucceeds());
+  if (child_pid == 0) {
+    // Busy wait without making any blocking syscalls.
+    auto end = absl::Now() + absl::Seconds(5);
+    while (absl::Now() < end) {
+    }
+    _exit(0);
+  }
+
+  absl::SleepFor(absl::Seconds(1));
+
+  // If only TID 1 is woken, thread.Join will hang.
+  // If only TID 2 is woken, both will hang.
+  a.store(1);
+  t.Join();
+
+  int status = 0;
+  EXPECT_THAT(RetryEINTR(waitpid)(child_pid, &status, 0), SyscallSucceeds());
+  EXPECT_TRUE(WIFEXITED(status));
+  EXPECT_EQ(WEXITSTATUS(status), 0);
+}
+
+// Test that multiple processes can execute concurrently, even if one process
+// never yields.
+TEST(ConcurrencyTest, MultiProcessConcurrency) {
+
+  pid_t child_pid;
+  ASSERT_THAT(child_pid = fork(), SyscallSucceeds());
+  if (child_pid == 0) {
+    while (true) {
+    }
+    __builtin_unreachable();
+  }
+
+  absl::SleepFor(absl::Seconds(5));
+
+  // We are still able to execute code in this process. The other hasn't
+  // permanently hung execution in both processes.
+  ASSERT_THAT(kill(child_pid, SIGKILL), SyscallSucceeds());
+  int status = 0;
+
+  ASSERT_THAT(RetryEINTR(waitpid)(child_pid, &status, 0), SyscallSucceeds());
+  ASSERT_TRUE(WIFSIGNALED(status));
+  ASSERT_EQ(WTERMSIG(status), SIGKILL);
+}
+
+}  // namespace
+}  // namespace testing
+}  // namespace gvisor