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Commit b30769a8 authored by Elliott Hughes's avatar Elliott Hughes
Browse files

Implement android::base::WaitForProperty. 

Also adapt libcutils to the bionic change that was necessary for this.

Bug: http://b/35201172
Test: ran tests
Change-Id: I72a98b70b03d23e958b46778b505fbd5c86c32ae
parent 7e7913cb

base/include/android-base/properties.h

+3 −0
Original line number Diff line number Diff line
@@ -58,6 +58,9 @@ template <typename T> T GetUintProperty(const std::string& key, 
// tell you whether or not your call succeeded. A `false` return value definitely means failure.

bool SetProperty(const std::string& key, const std::string& value);



// Waits for the system property `key` to have the value `expected_value`, .

void WaitForProperty(const std::string& key, const std::string& expected_value);



} // namespace base

} // namespace android

base/properties.cpp

+41 −0
Original line number Diff line number Diff line
@@ -14,9 +14,12 @@ 
 * limitations under the License.

 */



#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_



#include "android-base/properties.h"



#include <sys/system_properties.h>

#include <sys/_system_properties.h>



#include <string>
@@ -78,5 +81,43 @@ bool SetProperty(const std::string& key, const std::string& value) { 
  return (__system_property_set(key.c_str(), value.c_str()) == 0);

}



struct WaitForPropertyData {

  bool done;

  const std::string* expected_value;

  unsigned last_read_serial;

};



static void WaitForPropertyCallback(void* data_ptr, const char*, const char* value, unsigned serial) {

  WaitForPropertyData* data = reinterpret_cast<WaitForPropertyData*>(data_ptr);

  if (*data->expected_value == value) {

    data->done = true;

  } else {

    data->last_read_serial = serial;

  }

}



void WaitForProperty(const std::string& key, const std::string& expected_value) {

  // Find the property's prop_info*.

  const prop_info* pi;

  unsigned global_serial = 0;

  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.

    global_serial = __system_property_wait_any(global_serial);

  }



  WaitForPropertyData data;

  data.expected_value = &expected_value;

  data.done = false;

  while (true) {

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

    __system_property_read_callback(pi, WaitForPropertyCallback, &data);

    if (data.done) return;



    // It didn't so wait for it to change before checking again.

    __system_property_wait(pi, data.last_read_serial);

  }

}



}  // namespace base

}  // namespace android

base/properties_test.cpp

+20 −0
Original line number Diff line number Diff line
@@ -18,7 +18,12 @@ 


#include <gtest/gtest.h>



#include <atomic>

#include <chrono>

#include <string>

#include <thread>



using namespace std::chrono_literals;



TEST(properties, smoke) {

  android::base::SetProperty("debug.libbase.property_test", "hello");
@@ -119,3 +124,18 @@ TEST(properties, GetUintProperty_uint8_t) { CheckGetUintProperty<uint8_t>(); } 
TEST(properties, GetUintProperty_uint16_t) { CheckGetUintProperty<uint16_t>(); }

TEST(properties, GetUintProperty_uint32_t) { CheckGetUintProperty<uint32_t>(); }

TEST(properties, GetUintProperty_uint64_t) { CheckGetUintProperty<uint64_t>(); }



TEST(properties, WaitForProperty) {

  std::atomic<bool> flag{false};

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

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

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

    while (!flag) std::this_thread::yield();

    android::base::SetProperty("debug.libbase.WaitForProperty_test", "b");

  });



  android::base::WaitForProperty("debug.libbase.WaitForProperty_test", "a");

  flag = true;

  android::base::WaitForProperty("debug.libbase.WaitForProperty_test", "b");

  thread.join();

}

libcutils/properties.cpp

+1 −1
Original line number Diff line number Diff line
@@ -129,7 +129,7 @@ struct callback_data { 
    void* cookie;

};



static void trampoline(void* raw_data, const char* name, const char* value) {

static void trampoline(void* raw_data, const char* name, const char* value, unsigned /*serial*/) {

    callback_data* data = reinterpret_cast<callback_data*>(raw_data);

    data->callback(name, value, data->cookie);

}