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Workaround memory leak in dispatchers. (#119)
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* Workaround memory leak in dispatchers.

Android has a long-standing known issue where local variables aren't
explicitly cleared even when they go out of scope, which can cause
their contents to leak. Since BlockingQueue#take() blocks
forever until a new item is ready, this means the last
request will remain in memory until a new request pushes it
out. Extracting a helper method is a workaround for this - see, for
example, the following CL in the Android support lib:

https://android.googlesource.com/platform/frameworks/support/+/cd07a0cfd9c9501a03c574d2d48df51c82b73e33

The following other solutions were attempted but were not sufficient:

- Clear the variable prior to take() - optimized out because the write
  is not observable, so it has no impact on the bytecode.

- Call poll() prior to take() - for some reason, this doesn't work
  when proguard optimization is on.

With code optimization, there's no guarantee that this will work, though
we now provide a Proguard config that should prevent inlining. However, it
appears to be the best we can do and follows precedent / advice from the
ART team.

Should contain no functional changes otherwise as this is just
extracting code to a helper method, and thus should be safe for 1.1.0.

Verified against provided sample app.

Fixes #114
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@jpd236
jpd236 committed Nov 10, 2017
1 parent c3bd8e9 commit 536c1b7
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Showing 4 changed files with 145 additions and 119 deletions.
9 changes: 9 additions & 0 deletions consumer-proguard-rules.pro
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@@ -0,0 +1,9 @@
# Prevent Proguard from inlining methods that are intentionally extracted to ensure locals have a
# constrained liveness scope by the GC. This is needed to avoid keeping previous request references
# alive for an indeterminate amount of time. See also https://github.com/google/volley/issues/114
-keepclassmembers,allowshrinking,allowobfuscation class com.android.volley.NetworkDispatcher {
void processRequest();
}
-keepclassmembers,allowshrinking,allowobfuscation class com.android.volley.CacheDispatcher {
void processRequest();
}
4 changes: 4 additions & 0 deletions rules.gradle
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Expand Up @@ -9,6 +9,10 @@ android {
sourceCompatibility JavaVersion.VERSION_1_7
targetCompatibility JavaVersion.VERSION_1_7
}

defaultConfig {
consumerProguardFiles 'consumer-proguard-rules.pro'
}
}

// Check if the android plugin version supports unit testing.
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145 changes: 76 additions & 69 deletions src/main/java/com/android/volley/CacheDispatcher.java
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Expand Up @@ -93,82 +93,89 @@ public void run() {

while (true) {
try {
// Get a request from the cache triage queue, blocking until
// at least one is available.
final Request<?> request = mCacheQueue.take();
request.addMarker("cache-queue-take");

// If the request has been canceled, don't bother dispatching it.
if (request.isCanceled()) {
request.finish("cache-discard-canceled");
continue;
processRequest();
} catch (InterruptedException e) {
// We may have been interrupted because it was time to quit.
if (mQuit) {
return;
}
}
}
}

// Attempt to retrieve this item from cache.
Cache.Entry entry = mCache.get(request.getCacheKey());
if (entry == null) {
request.addMarker("cache-miss");
// Cache miss; send off to the network dispatcher.
if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
mNetworkQueue.put(request);
}
continue;
}
// Extracted to its own method to ensure locals have a constrained liveness scope by the GC.
// This is needed to avoid keeping previous request references alive for an indeterminate amount
// of time. Update consumer-proguard-rules.pro when modifying this. See also
// https://github.com/google/volley/issues/114
private void processRequest() throws InterruptedException {
// Get a request from the cache triage queue, blocking until
// at least one is available.
final Request<?> request = mCacheQueue.take();
request.addMarker("cache-queue-take");

// If it is completely expired, just send it to the network.
if (entry.isExpired()) {
request.addMarker("cache-hit-expired");
request.setCacheEntry(entry);
if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
mNetworkQueue.put(request);
}
continue;
}
// If the request has been canceled, don't bother dispatching it.
if (request.isCanceled()) {
request.finish("cache-discard-canceled");
return;
}

// We have a cache hit; parse its data for delivery back to the request.
request.addMarker("cache-hit");
Response<?> response = request.parseNetworkResponse(
new NetworkResponse(entry.data, entry.responseHeaders));
request.addMarker("cache-hit-parsed");
// Attempt to retrieve this item from cache.
Cache.Entry entry = mCache.get(request.getCacheKey());
if (entry == null) {
request.addMarker("cache-miss");
// Cache miss; send off to the network dispatcher.
if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
mNetworkQueue.put(request);
}
return;
}

if (!entry.refreshNeeded()) {
// Completely unexpired cache hit. Just deliver the response.
mDelivery.postResponse(request, response);
} else {
// Soft-expired cache hit. We can deliver the cached response,
// but we need to also send the request to the network for
// refreshing.
request.addMarker("cache-hit-refresh-needed");
request.setCacheEntry(entry);
// Mark the response as intermediate.
response.intermediate = true;
// If it is completely expired, just send it to the network.
if (entry.isExpired()) {
request.addMarker("cache-hit-expired");
request.setCacheEntry(entry);
if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
mNetworkQueue.put(request);
}
return;
}

if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
// Post the intermediate response back to the user and have
// the delivery then forward the request along to the network.
mDelivery.postResponse(request, response, new Runnable() {
@Override
public void run() {
try {
mNetworkQueue.put(request);
} catch (InterruptedException e) {
// Restore the interrupted status
Thread.currentThread().interrupt();
}
}
});
} else {
// request has been added to list of waiting requests
// to receive the network response from the first request once it returns.
mDelivery.postResponse(request, response);
}
}
// We have a cache hit; parse its data for delivery back to the request.
request.addMarker("cache-hit");
Response<?> response = request.parseNetworkResponse(
new NetworkResponse(entry.data, entry.responseHeaders));
request.addMarker("cache-hit-parsed");

} catch (InterruptedException e) {
// We may have been interrupted because it was time to quit.
if (mQuit) {
return;
}
if (!entry.refreshNeeded()) {
// Completely unexpired cache hit. Just deliver the response.
mDelivery.postResponse(request, response);
} else {
// Soft-expired cache hit. We can deliver the cached response,
// but we need to also send the request to the network for
// refreshing.
request.addMarker("cache-hit-refresh-needed");
request.setCacheEntry(entry);
// Mark the response as intermediate.
response.intermediate = true;

if (!mWaitingRequestManager.maybeAddToWaitingRequests(request)) {
// Post the intermediate response back to the user and have
// the delivery then forward the request along to the network.
mDelivery.postResponse(request, response, new Runnable() {
@Override
public void run() {
try {
mNetworkQueue.put(request);
} catch (InterruptedException e) {
// Restore the interrupted status
Thread.currentThread().interrupt();
}
}
});
} else {
// request has been added to list of waiting requests
// to receive the network response from the first request once it returns.
mDelivery.postResponse(request, response);
}
}
}
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106 changes: 56 additions & 50 deletions src/main/java/com/android/volley/NetworkDispatcher.java
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Expand Up @@ -83,70 +83,76 @@ private void addTrafficStatsTag(Request<?> request) {
public void run() {
Process.setThreadPriority(Process.THREAD_PRIORITY_BACKGROUND);
while (true) {
long startTimeMs = SystemClock.elapsedRealtime();
Request<?> request;
try {
// Take a request from the queue.
request = mQueue.take();
processRequest();
} catch (InterruptedException e) {
// We may have been interrupted because it was time to quit.
if (mQuit) {
return;
}
continue;
}
}
}

try {
request.addMarker("network-queue-take");

// If the request was cancelled already, do not perform the
// network request.
if (request.isCanceled()) {
request.finish("network-discard-cancelled");
request.notifyListenerResponseNotUsable();
continue;
}

addTrafficStatsTag(request);
// Extracted to its own method to ensure locals have a constrained liveness scope by the GC.
// This is needed to avoid keeping previous request references alive for an indeterminate amount
// of time. Update consumer-proguard-rules.pro when modifying this. See also
// https://github.com/google/volley/issues/114
private void processRequest() throws InterruptedException {
long startTimeMs = SystemClock.elapsedRealtime();
// Take a request from the queue.
Request<?> request = mQueue.take();

try {
request.addMarker("network-queue-take");

// If the request was cancelled already, do not perform the
// network request.
if (request.isCanceled()) {
request.finish("network-discard-cancelled");
request.notifyListenerResponseNotUsable();
return;
}

// Perform the network request.
NetworkResponse networkResponse = mNetwork.performRequest(request);
request.addMarker("network-http-complete");
addTrafficStatsTag(request);

// If the server returned 304 AND we delivered a response already,
// we're done -- don't deliver a second identical response.
if (networkResponse.notModified && request.hasHadResponseDelivered()) {
request.finish("not-modified");
request.notifyListenerResponseNotUsable();
continue;
}
// Perform the network request.
NetworkResponse networkResponse = mNetwork.performRequest(request);
request.addMarker("network-http-complete");

// Parse the response here on the worker thread.
Response<?> response = request.parseNetworkResponse(networkResponse);
request.addMarker("network-parse-complete");
// If the server returned 304 AND we delivered a response already,
// we're done -- don't deliver a second identical response.
if (networkResponse.notModified && request.hasHadResponseDelivered()) {
request.finish("not-modified");
request.notifyListenerResponseNotUsable();
return;
}

// Write to cache if applicable.
// TODO: Only update cache metadata instead of entire record for 304s.
if (request.shouldCache() && response.cacheEntry != null) {
mCache.put(request.getCacheKey(), response.cacheEntry);
request.addMarker("network-cache-written");
}
// Parse the response here on the worker thread.
Response<?> response = request.parseNetworkResponse(networkResponse);
request.addMarker("network-parse-complete");

// Post the response back.
request.markDelivered();
mDelivery.postResponse(request, response);
request.notifyListenerResponseReceived(response);
} catch (VolleyError volleyError) {
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
parseAndDeliverNetworkError(request, volleyError);
request.notifyListenerResponseNotUsable();
} catch (Exception e) {
VolleyLog.e(e, "Unhandled exception %s", e.toString());
VolleyError volleyError = new VolleyError(e);
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
mDelivery.postError(request, volleyError);
request.notifyListenerResponseNotUsable();
// Write to cache if applicable.
// TODO: Only update cache metadata instead of entire record for 304s.
if (request.shouldCache() && response.cacheEntry != null) {
mCache.put(request.getCacheKey(), response.cacheEntry);
request.addMarker("network-cache-written");
}

// Post the response back.
request.markDelivered();
mDelivery.postResponse(request, response);
request.notifyListenerResponseReceived(response);
} catch (VolleyError volleyError) {
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
parseAndDeliverNetworkError(request, volleyError);
request.notifyListenerResponseNotUsable();
} catch (Exception e) {
VolleyLog.e(e, "Unhandled exception %s", e.toString());
VolleyError volleyError = new VolleyError(e);
volleyError.setNetworkTimeMs(SystemClock.elapsedRealtime() - startTimeMs);
mDelivery.postError(request, volleyError);
request.notifyListenerResponseNotUsable();
}
}

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