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Commit e2d986da authored by Keun-young Park's avatar Keun-young Park
Browse files

add base::WaitForPropertyCreation 

- unlike base::WaitForProperty, which waits for specific value to
  be set, this one only waits until the property is created.

bug: 35178781
Test: added unit test
Change-Id: Idbf98c2152fe768357302f6b69310c55305f5d54
parent f719c255

base/include/android-base/properties.h

+6 −0
Original line number Diff line number Diff line
@@ -66,6 +66,12 @@ bool WaitForProperty(const std::string& key, 
                     const std::string& expected_value,

                     std::chrono::milliseconds relative_timeout);



// Waits for the system property `key` to be created.

// Times out after `relative_timeout`.

// Returns true on success, false on timeout.

bool WaitForPropertyCreation(const std::string& key,

                             std::chrono::milliseconds relative_timeout);



} // namespace base

} // namespace android

base/properties.cpp

+29 −7
Original line number Diff line number Diff line
@@ -108,8 +108,10 @@ static void DurationToTimeSpec(timespec& ts, std::chrono::nanoseconds d) { 
  ts.tv_nsec = ns.count();

}



using AbsTime = std::chrono::time_point<std::chrono::steady_clock>;



static void UpdateTimeSpec(timespec& ts,

                           const std::chrono::time_point<std::chrono::steady_clock>& timeout) {

                           const AbsTime& timeout) {

  auto now = std::chrono::steady_clock::now();

  auto remaining_timeout = std::chrono::duration_cast<std::chrono::nanoseconds>(timeout - now);

  if (remaining_timeout < 0ns) {
@@ -119,13 +121,16 @@ static void UpdateTimeSpec(timespec& ts, 
  }

}



bool WaitForProperty(const std::string& key,

                     const std::string& expected_value,

                     std::chrono::milliseconds relative_timeout) {

// Waits for the system property `key` to be created.

// Times out after `relative_timeout`.

// Sets absolute_timeout which represents absolute time for the timeout.

// Returns nullptr on timeout.

static const prop_info* WaitForPropertyCreation(const std::string& key,

                                                const std::chrono::milliseconds& relative_timeout,

                                                AbsTime& absolute_timeout) {

  // TODO: boot_clock?

  auto now = std::chrono::steady_clock::now();

  std::chrono::time_point<std::chrono::steady_clock> absolute_timeout = now + relative_timeout;

  timespec ts;

  absolute_timeout = now + relative_timeout;



  // Find the property's prop_info*.

  const prop_info* pi;
@@ -133,14 +138,25 @@ bool WaitForProperty(const std::string& key, 
  while ((pi = __system_property_find(key.c_str())) == nullptr) {

    // The property doesn't even exist yet.

    // Wait for a global change and then look again.

    timespec ts;

    UpdateTimeSpec(ts, absolute_timeout);

    if (!__system_property_wait(nullptr, global_serial, &global_serial, &ts)) return false;

    if (!__system_property_wait(nullptr, global_serial, &global_serial, &ts)) return nullptr;

  }

  return pi;

}



bool WaitForProperty(const std::string& key,

                     const std::string& expected_value,

                     std::chrono::milliseconds relative_timeout) {

  AbsTime absolute_timeout;

  const prop_info* pi = WaitForPropertyCreation(key, relative_timeout, absolute_timeout);

  if (pi == nullptr) return false;



  WaitForPropertyData data;

  data.expected_value = &expected_value;

  data.done = false;

  while (true) {

    timespec ts;

    // Check whether the property has the value we're looking for?

    __system_property_read_callback(pi, WaitForPropertyCallback, &data);

    if (data.done) return true;
@@ -152,5 +168,11 @@ bool WaitForProperty(const std::string& key, 
  }

}



bool WaitForPropertyCreation(const std::string& key,

                             std::chrono::milliseconds relative_timeout) {

  AbsTime absolute_timeout;

  return (WaitForPropertyCreation(key, relative_timeout, absolute_timeout) != nullptr);

}



}  // namespace base

}  // namespace android

base/properties_test.cpp

+22 −0
Original line number Diff line number Diff line
@@ -150,3 +150,25 @@ TEST(properties, WaitForProperty_timeout) { 
  // Upper bounds on timing are inherently flaky, but let's try...

  ASSERT_LT(std::chrono::duration_cast<std::chrono::milliseconds>(t1 - t0), 600ms);

}



TEST(properties, WaitForPropertyCreation) {

  std::thread thread([&]() {

    std::this_thread::sleep_for(100ms);

    android::base::SetProperty("debug.libbase.WaitForPropertyCreation_test", "a");

  });



  ASSERT_TRUE(android::base::WaitForPropertyCreation(

          "debug.libbase.WaitForPropertyCreation_test", 1s));

  thread.join();

}



TEST(properties, WaitForPropertyCreation_timeout) {

  auto t0 = std::chrono::steady_clock::now();

  ASSERT_FALSE(android::base::WaitForPropertyCreation(

          "debug.libbase.WaitForPropertyCreation_timeout_test", 200ms));

  auto t1 = std::chrono::steady_clock::now();



  ASSERT_GE(std::chrono::duration_cast<std::chrono::milliseconds>(t1 - t0), 200ms);

  // Upper bounds on timing are inherently flaky, but let's try...

  ASSERT_LT(std::chrono::duration_cast<std::chrono::milliseconds>(t1 - t0), 600ms);

}