Add ScopedTaskSuspend and its test

util/mach/scoped_task_suspend_test.cc

+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// 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 "util/mach/scoped_task_suspend.h"
+
+#include <mach/mach.h>
+#include <stdint.h>
+
+#include <algorithm>
+
+#include "gtest/gtest.h"
+#include "util/file/fd_io.h"
+#include "util/mach/task_memory.h"
+#include "util/misc/clock.h"
+#include "util/test/mac/mach_multiprocess.h"
+
+namespace crashpad {
+namespace test {
+namespace {
+
+class ScopedTaskSuspendTest final : public MachMultiprocess {
+ public:
+  ScopedTaskSuspendTest() : MachMultiprocess() {}
+  ~ScopedTaskSuspendTest() {}
+
+ private:
+  // Reads the int at |address| from the child process’ memory at |task_memory|.
+  static int CounterValue(TaskMemory* task_memory, mach_vm_address_t address) {

[Robert Sesek, 2014/10/13 15:01:37]

Does this test really need to use TaskMemory? Could you instead test if the task
suspension works by merely messaging over the shared pipe instead?

+    int counter = 0;
+    EXPECT_TRUE(task_memory->Read(address, sizeof(counter), &counter));
+    return counter;
+  }
+
+  // Determines whether the child process is updating its counter. The counter
+  // is expected to be updated while the child process is running, but should
+  // appear frozen while the child process is suspended.
+  static bool CounterIsRunning(
+      TaskMemory* task_memory, mach_vm_address_t address) {
+    int initial_counter = CounterValue(task_memory, address);
+
+    // Look for any change in the counter. If there is any change, the counter
+    // is running. If there is no change, it doesn’t necessarily mean that the
+    // child process is suspended, because it may not have been scheduled for
+    // another reason. Retry a few times in a loop with a delay.
+    for (size_t tries = 10; tries > 0; --tries) {
+      SleepNanoseconds(1E5);  // 100 microseconds
+
+      int counter = CounterValue(task_memory, address);
+      if (counter != initial_counter) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+
+  // MachMultiprocess:
+
+  virtual void MachMultiprocessParent() override {
+    int read_fd = ReadPipeFD();
+
+    // Get the address of the counter in the child process.
+    mach_vm_address_t address;
+    CheckedReadFD(read_fd, &address, sizeof(address));
+
+    task_t child_task = ChildTask();
+    TaskMemory task_memory(child_task);
+
+    // In the initial state, the child process should be scheduled, and it
+    // should be updating its counter.
+    EXPECT_TRUE(CounterIsRunning(&task_memory, address));
+
+    {
+      // Suspend the child process.
+      ScopedTaskSuspend suspend(child_task);
+
+      // CounterIsRunning() just makes sure that the child process is not
+      // running within a short duration. Checking the counter value before and
+      // after the sleep ensures that the child process has not run during a
+      // larger period that it was expected to be suspended.
+      int initial_value = CounterValue(&task_memory, address);
+
+      EXPECT_FALSE(CounterIsRunning(&task_memory, address));
+
+      // Sleep for a little while, giving the child process a chance to measure
+      // that one of its loop iterations took a long time.
+      SleepNanoseconds(1E6);  // 1 millisecond
+
+      EXPECT_FALSE(CounterIsRunning(&task_memory, address));
+
+      // Make sure that the child process hasn’t had a chance to run at all.
+      int final_value = CounterValue(&task_memory, address);
+      EXPECT_EQ(initial_value, final_value);
+    }
+
+    // The suspension should no longer be placed, and the child process should
+    // be running again. This makes sure that when the counter was seen as
+    // stopped before, it’s because the child process was really suspended, and
+    // not because it had exited its loop.
+    EXPECT_TRUE(CounterIsRunning(&task_memory, address));
+
+    // Get the child’s idea of its final counter value, and compare that against
+    // this process’ idea of the same value. This tests that CounterValue() was
+    // in fact reading the right value from the child process.
+    int expect_counter;
+    CheckedReadFD(read_fd, &expect_counter, sizeof(expect_counter));
+
+    int counter = CounterValue(&task_memory, address);
+    EXPECT_EQ(expect_counter, counter);
+  }
+
+  virtual void MachMultiprocessChild() override {
+    int write_fd = WritePipeFD();
+
+    // Tell the parent process where to find the counter in this process’
+    // address space.
+    volatile int counter = 0;
+    mach_vm_address_t address = reinterpret_cast<mach_vm_address_t>(&counter);
+    CheckedWriteFD(write_fd, &address, sizeof(address));
+
+    // Loop for a while, computing the longest duration for an iteration of the
+    // loop. Inside each loop, update the counter, which the parent process can
+    // examine to see whether the loop is running from its perspective.
+    uint64_t start = ClockMonotonicNanoseconds();
+    uint64_t deadline = start + 1E8;  // 100 milliseconds
+    uint64_t now = start;
+    uint64_t last = now;
+    uint64_t max_delay = 0;
+    do {
+      ++counter;
+      uint64_t delay = now - last;
+      max_delay = std::max(max_delay, delay);
+      last = now;
+    } while ((now = ClockMonotonicNanoseconds()) < deadline);
+
+    // The longest iteration of the loop should be at least as long as the time
+    // that the parent process had this process suspended, but because of the
+    // tricky nature of scheduling, just make sure that the longest iteration
+    // took a perceptible amount of time.
+    EXPECT_GE(max_delay, 1E5);  // 100 microseconds
+
+    // Tell the parent process where the counter ended up.
+    CheckedWriteFD(write_fd, const_cast<int*>(&counter), sizeof(counter));
+
+    // Wait for the parent process to finish reading this process’ memory.
+    CheckedReadFDAtEOF(ReadPipeFD());
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedTaskSuspendTest);
+};
+
+TEST(ScopedTaskSuspend, ScopedTaskSuspend) {
+  ScopedTaskSuspendTest scoped_task_suspend_test;
+  scoped_task_suspend_test.Run();
+}
+
+}  // namespace
+}  // namespace test
+}  // namespace crashpad