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Handle configuration fetching vs. cache race condition #49
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Original file line number | Diff line number | Diff line change |
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@@ -42,11 +42,14 @@ | |
import java.lang.reflect.Type; | ||
import java.lang.reflect.Field; | ||
import java.util.List; | ||
import java.util.concurrent.ConcurrentHashMap; | ||
import java.util.concurrent.CountDownLatch; | ||
import java.util.concurrent.TimeUnit; | ||
import java.util.stream.Collectors; | ||
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import cloud.eppo.android.dto.EppoValue; | ||
import cloud.eppo.android.dto.FlagConfig; | ||
import cloud.eppo.android.dto.RandomizationConfigResponse; | ||
import cloud.eppo.android.dto.SubjectAttributes; | ||
import cloud.eppo.android.dto.deserializers.EppoValueAdapter; | ||
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@@ -99,9 +102,6 @@ static class AssignmentValueTypeAdapter implements JsonDeserializer<AssignmentVa | |
this.defaultValue = defaultValue; | ||
} | ||
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AssignmentValueTypeAdapter() { | ||
} | ||
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@Override | ||
public AssignmentValueType deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) | ||
throws JsonParseException { | ||
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@@ -159,8 +159,9 @@ public void onError(String errorMessage) { | |
// Wait for initialization to succeed or fail, up to 10 seconds, before continuing | ||
try { | ||
if (!lock.await(10000, TimeUnit.MILLISECONDS)) { | ||
throw new InterruptedException("Request for RAC did not complete within timeout"); | ||
throw new InterruptedException("Client initialization not complete within timeout"); | ||
} | ||
Log.d(TAG, "Test client initialized"); | ||
} catch (InterruptedException e) { | ||
throw new RuntimeException(e); | ||
} | ||
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@@ -172,6 +173,9 @@ public void clearCaches() { | |
for (String apiKey : apiKeys) { | ||
clearCacheFile(apiKey); | ||
} | ||
// Reset any development overrides | ||
setHttpClientOverrideField(null); | ||
setConfigurationStoreOverrideField(null); | ||
} | ||
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private void clearCacheFile(String apiKey) { | ||
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@@ -371,27 +375,8 @@ public void testInvalidConfigJSON() { | |
return null; // doAnswer doesn't require a return value | ||
}).when(mockHttpClient).get(anyString(), any(RequestCallback.class)); | ||
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Field httpClientOverrideField = null; | ||
try { | ||
// Use reflection to set the httpClientOverride field | ||
httpClientOverrideField = EppoClient.class.getDeclaredField("httpClientOverride"); | ||
httpClientOverrideField.setAccessible(true); | ||
httpClientOverrideField.set(null, mockHttpClient); | ||
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initClient(TEST_HOST, true, true, false, DUMMY_API_KEY); | ||
} catch (NoSuchFieldException | IllegalAccessException e) { | ||
throw new RuntimeException(e); | ||
} finally { | ||
if (httpClientOverrideField != null) { | ||
try { | ||
httpClientOverrideField.set(null, null); | ||
} catch (IllegalAccessException e) { | ||
throw new RuntimeException(e); | ||
} | ||
httpClientOverrideField.setAccessible(false); | ||
} | ||
} | ||
setHttpClientOverrideField(mockHttpClient); | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Cleaned up the modification of the private static override variables into a little helper function 🧹 |
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initClient(TEST_HOST, true, true, false, DUMMY_API_KEY); | ||
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String result = EppoClient.getInstance().getStringAssignment("dummy subject", "dummy flag"); | ||
assertNull(result); | ||
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@@ -429,6 +414,7 @@ public void testDifferentCacheFilesPerKey() { | |
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// Pre-seed a different flag configuration for the other API Key | ||
ConfigCacheFile cacheFile2 = new ConfigCacheFile(ApplicationProvider.getApplicationContext(), safeCacheKey(DUMMY_OTHER_API_KEY)); | ||
// Set the experiment_with_boolean_variations flag to always return true | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. This comment is unrelated to the fix in this PR, but useful for that test |
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cacheFile2.setContents("{\n" + | ||
" \"flags\": {\n" + | ||
" \"8fc1fb33379d78c8a9edbf43afd6703a\": {\n" + | ||
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@@ -476,6 +462,41 @@ public void testDifferentCacheFilesPerKey() { | |
assertFalse(apiKey1Assignment); | ||
} | ||
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@Test | ||
public void testFetchCompletesBeforeCacheLoad() { | ||
Comment on lines
+465
to
+466
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. This is the test that reproduced the issue (and after the fix, verified it is handled correctly) 💪 |
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ConfigurationStore slowStore = new ConfigurationStore(ApplicationProvider.getApplicationContext(), safeCacheKey(DUMMY_API_KEY)) { | ||
@Override | ||
protected RandomizationConfigResponse readCacheFile() { | ||
Log.d(TAG, "Simulating slow cache read start"); | ||
try { | ||
Thread.sleep(2000); | ||
} catch (InterruptedException ex) { | ||
throw new RuntimeException(ex); | ||
} | ||
RandomizationConfigResponse response = new RandomizationConfigResponse(); | ||
ConcurrentHashMap<String, FlagConfig> mockFlags = new ConcurrentHashMap<>(); | ||
mockFlags.put("dummy", new FlagConfig()); // make the map non-empty | ||
response.setFlags(mockFlags); | ||
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Log.d(TAG, "Simulating slow cache read end"); | ||
return response; | ||
} | ||
}; | ||
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setConfigurationStoreOverrideField(slowStore); | ||
initClient(TEST_HOST, true, false, false, DUMMY_API_KEY); | ||
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// Give time for async slow cache read to finish | ||
try { | ||
Thread.sleep(2500); | ||
} catch (InterruptedException ex) { | ||
throw new RuntimeException(ex); | ||
} | ||
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String assignment = EppoClient.getInstance().getStringAssignment("6255e1a7d1a3025a26078b95", "randomization_algo"); | ||
assertEquals("green", assignment); | ||
} | ||
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private void waitForPopulatedCache() { | ||
long waitStart = System.currentTimeMillis(); | ||
long waitEnd = waitStart + 10 * 1000; // allow up to 10 seconds | ||
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@@ -497,22 +518,22 @@ private void waitForPopulatedCache() { | |
} | ||
} | ||
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private void waitForNonNullAssignment() { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. 🪓 Not used |
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long waitStart = System.currentTimeMillis(); | ||
long waitEnd = waitStart + 15 * 1000; // allow up to 15 seconds | ||
String assignment = null; | ||
private void setHttpClientOverrideField(EppoHttpClient httpClient) { | ||
setOverrideField("httpClientOverride", httpClient); | ||
} | ||
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private void setConfigurationStoreOverrideField(ConfigurationStore configurationStore) { | ||
setOverrideField("configurationStoreOverride", configurationStore); | ||
} | ||
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private <T> void setOverrideField(String fieldName, T override) { | ||
try { | ||
while (assignment == null) { | ||
if (System.currentTimeMillis() > waitEnd) { | ||
throw new InterruptedException("Non-null assignment never received; assuming configuration not loaded"); | ||
} | ||
// Uses third subject in test-case-0 | ||
assignment = EppoClient.getInstance().getStringAssignment("6255e1a7fc33a9c050ce9508", "randomization_algo"); | ||
if (assignment == null) { | ||
Thread.sleep(100); | ||
} | ||
} | ||
} catch (InterruptedException e) { | ||
// Use reflection to set the httpClientOverride field | ||
Field httpClientOverrideField = EppoClient.class.getDeclaredField(fieldName); | ||
httpClientOverrideField.setAccessible(true); | ||
httpClientOverrideField.set(null, override); | ||
httpClientOverrideField.setAccessible(false); | ||
} catch (NoSuchFieldException | IllegalAccessException e) { | ||
throw new RuntimeException(e); | ||
} | ||
} | ||
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Original file line number | Diff line number | Diff line change |
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@@ -24,45 +24,50 @@ public ConfigurationRequestor(ConfigurationStore configurationStore, EppoHttpCli | |
} | ||
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public void load(InitializationCallback callback) { | ||
AtomicBoolean cachedUsed = new AtomicBoolean(false); | ||
AtomicBoolean callbackCalled = new AtomicBoolean(false); | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Instead of tracking cache usage, we just track if the callback has been called yet. This way both fetch won't call the callback if the cache load finished first, and the cache load won't call the callback if the fetch finished first. |
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configurationStore.loadFromCache(new CacheLoadCallback() { | ||
@Override | ||
public void onCacheLoadSuccess() { | ||
cachedUsed.set(true); | ||
if (callback != null) { | ||
if (callback != null && callbackCalled.compareAndSet(false, true)) { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more.
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Log.d(TAG, "Initialized from cache"); | ||
callback.onCompleted(); | ||
} | ||
} | ||
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@Override | ||
public void onCacheLoadFail() { | ||
cachedUsed.set(false); | ||
// no-op; fall-back to Fetch | ||
} | ||
}); | ||
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Log.d(TAG, "Fetching configuration"); | ||
client.get("/api/randomized_assignment/v3/config", new RequestCallback() { | ||
@Override | ||
public void onSuccess(Reader response) { | ||
try { | ||
Log.d(TAG, "Processing fetch response"); | ||
configurationStore.setFlagsFromResponse(response); | ||
Log.d(TAG, "Configuration fetch successful"); | ||
} catch (JsonSyntaxException | JsonIOException e) { | ||
Log.e(TAG, "Error loading configuration response", e); | ||
if (callback != null && !cachedUsed.get()) { | ||
if (callback != null && callbackCalled.compareAndSet(false, true)) { | ||
Log.d(TAG, "Initialization failure due to fetch response"); | ||
callback.onError("Unable to request configuration"); | ||
} | ||
return; | ||
} | ||
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if (callback != null && !cachedUsed.get()) { | ||
if (callback != null && callbackCalled.compareAndSet(false, true)) { | ||
Log.d(TAG, "Initialized from fetch"); | ||
callback.onCompleted(); | ||
} | ||
} | ||
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@Override | ||
public void onFailure(String errorMessage) { | ||
Log.e(TAG, "Error fetching configuration: " + errorMessage); | ||
if (callback != null && !cachedUsed.get()) { | ||
if (callback != null && callbackCalled.compareAndSet(false, true)) { | ||
Log.d(TAG, "Initialization failure due to fetch error"); | ||
callback.onError(errorMessage); | ||
} | ||
} | ||
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Original file line number | Diff line number | Diff line change |
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@@ -12,8 +12,10 @@ | |
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import java.io.BufferedReader; | ||
import java.io.BufferedWriter; | ||
import java.io.IOException; | ||
import java.io.Reader; | ||
import java.util.concurrent.ConcurrentHashMap; | ||
import java.util.concurrent.atomic.AtomicBoolean; | ||
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import cloud.eppo.android.dto.EppoValue; | ||
import cloud.eppo.android.dto.FlagConfig; | ||
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@@ -33,6 +35,7 @@ public class ConfigurationStore { | |
.create(); | ||
private final ConfigCacheFile cacheFile; | ||
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private AtomicBoolean loadedFromFetchResponse = new AtomicBoolean(false); | ||
private ConcurrentHashMap<String, FlagConfig> flags; | ||
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public ConfigurationStore(Application application, String cacheFileNameSuffix) { | ||
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@@ -49,19 +52,20 @@ public void loadFromCache(CacheLoadCallback callback) { | |
AsyncTask.execute(() -> { | ||
Log.d(TAG, "Loading from cache"); | ||
try { | ||
RandomizationConfigResponse configResponse; | ||
synchronized (cacheFile) { | ||
BufferedReader reader = cacheFile.getReader(); | ||
configResponse = gson.fromJson(reader, RandomizationConfigResponse.class); | ||
reader.close(); | ||
} | ||
RandomizationConfigResponse configResponse = readCacheFile(); | ||
if (configResponse == null || configResponse.getFlags() == null) { | ||
throw new JsonSyntaxException("Configuration file missing flags"); | ||
throw new JsonSyntaxException("Cached configuration file missing flags"); | ||
} | ||
flags = configResponse.getFlags(); | ||
if (flags.isEmpty()) { | ||
if (configResponse.getFlags().isEmpty()) { | ||
throw new IllegalStateException("Cached configuration file has empty flags"); | ||
} | ||
if (loadedFromFetchResponse.get()) { | ||
Log.w(TAG, "Configuration already updated via fetch; ignoring cache"); | ||
callback.onCacheLoadFail(); | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Considering this a cache failure. Conceptually it sort of is as the cache was too slow 😛 |
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return; | ||
} | ||
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flags = configResponse.getFlags(); | ||
Log.d(TAG, "Cache loaded successfully"); | ||
callback.onCacheLoadSuccess(); | ||
} catch (Exception e) { | ||
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@@ -72,14 +76,25 @@ public void loadFromCache(CacheLoadCallback callback) { | |
}); | ||
} | ||
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protected RandomizationConfigResponse readCacheFile() throws IOException { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Pulled this out so it can be mocked by tests, but it cleans things up a bit too. |
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RandomizationConfigResponse configResponse; | ||
synchronized (cacheFile) { | ||
BufferedReader reader = cacheFile.getReader(); | ||
configResponse = gson.fromJson(reader, RandomizationConfigResponse.class); | ||
reader.close(); | ||
} | ||
return configResponse; | ||
} | ||
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public void setFlagsFromResponse(Reader response) { | ||
RandomizationConfigResponse config = gson.fromJson(response, RandomizationConfigResponse.class); | ||
if (config == null || config.getFlags() == null) { | ||
Log.w(TAG, "Flags missing in configuration response"); | ||
flags = new ConcurrentHashMap<>(); | ||
} else { | ||
flags = config.getFlags(); | ||
Log.d(TAG, "Loaded" + flags.size() + "flags from configuration response"); | ||
loadedFromFetchResponse.set(true); // Record that flags were set from a response so we don't later clobber them with a slow cache read | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. seems like flags could still be overwritten if flags are set here, then in the cached method before line 96 runs, right? if so, we can move this to a line above/before setting flags There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. good catch, let's move this above! |
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Log.d(TAG, "Loaded " + flags.size() + " flags from configuration response"); | ||
} | ||
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writeConfigToFile(config); | ||
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Original file line number | Diff line number | Diff line change |
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@@ -36,14 +36,16 @@ public class EppoClient { | |
private boolean isGracefulMode; | ||
private static EppoClient instance; | ||
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// Useful for testing in situations where we want to mock the http client | ||
// Useful for testing in situations where we want to mock the http client or configuration store | ||
private static EppoHttpClient httpClientOverride = null; | ||
private static ConfigurationStore configurationStoreOverride = null; | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. give the ability for tests to use reflection to inject a configuration store without complicating the public "API" of this class. |
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private EppoClient(Application application, String apiKey, String host, AssignmentLogger assignmentLogger, | ||
boolean isGracefulMode) { | ||
EppoHttpClient httpClient = httpClientOverride == null ? new EppoHttpClient(host, apiKey) : httpClientOverride; | ||
String cacheFileNameSuffix = safeCacheKey(apiKey); // Cache at a per-API key level (useful for development) | ||
ConfigurationStore configStore = new ConfigurationStore(application, cacheFileNameSuffix); | ||
ConfigurationStore configStore = configurationStoreOverride == null ? new ConfigurationStore(application, cacheFileNameSuffix) : configurationStoreOverride; | ||
requestor = new ConfigurationRequestor(configStore, httpClient); | ||
this.isGracefulMode = isGracefulMode; | ||
this.assignmentLogger = assignmentLogger; | ||
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🪓 Wasn't used