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[ios] Fix a race condition issue in the Mapbox metrics class. #15029

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[ios] Fix a race condition issue in the Mapbox metrics class. #15029

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6f00330
[ios] Fix a race condition issue in the Mapbox metrics class.
fabian-guerra Jun 29, 2019
936c0eb
[ios] Changelog update.
fabian-guerra Jul 1, 2019
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17 changes: 11 additions & 6 deletions platform/darwin/src/MGLNetworkConfiguration.m
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Expand Up @@ -65,9 +65,13 @@ - (NSURLSessionConfiguration *)defaultSessionConfiguration {
}

- (void)startDownloadEvent:(NSString *)urlString type:(NSString *)resourceType {
if (urlString && ![self.events objectForKey:urlString]) {
[self.events setObject:@{ MGLStartTime: [NSDate date], MGLResourceType: resourceType } forKey:urlString];
NSString *retainedUrlString = urlString;
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I don't think this is sufficient. AFAIK urlString should be retained by this method anyway - how about using copy here?

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I consider using copy but an increase in the retain count would do the job better.

NSString *retainedResourceType = resourceType;
if (retainedUrlString && !self.events[retainedUrlString]) {
self.events[retainedUrlString] = @{ MGLStartTime: [NSDate date], MGLResourceType: retainedResourceType };
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I think we need to change the events property to be atomic:

@property (atomic, strong) NSMutableDictionary<NSString*, NSDictionary*> *events;

since reading/writing/deleting could happen at the same time.

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This property gets called multiple times. I consider the atomicity but in practice found no reason to make this an atomic property when the crash is raised for a different reason.

}
retainedUrlString = nil;
retainedResourceType = nil;
}

- (void)stopDownloadEventForResponse:(NSURLResponse *)response {
Expand All @@ -80,15 +84,16 @@ - (void)cancelDownloadEventForResponse:(NSURLResponse *)response {

- (void)sendEventForURLResponse:(NSURLResponse *)response withAction:(NSString *)action
{
if ([response isKindOfClass:[NSURLResponse class]]) {
NSString *urlString = response.URL.relativePath;
NSURLResponse *retainedResponse = response;
if ([retainedResponse isKindOfClass:[NSURLResponse class]]) {
NSString *urlString = retainedResponse.URL.relativePath;
if (urlString && [self.events objectForKey:urlString]) {
NSDictionary *eventAttributes = [self eventAttributesForURL:response withAction:action];
NSDictionary *eventAttributes = [self eventAttributesForURL:retainedResponse withAction:action];
[self.metricsDelegate networkConfiguration:self didGenerateMetricEvent:eventAttributes];
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We should dispatch this delegate call on the main queue.

[self.events removeObjectForKey:urlString];
}
}

retainedResponse = nil;
}

- (NSDictionary *)eventAttributesForURL:(NSURLResponse *)response withAction:(NSString *)action
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1 change: 1 addition & 0 deletions platform/ios/CHANGELOG.md
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Expand Up @@ -7,6 +7,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
### Offline maps

* Fixed an issue where offline regions could report the wrong number of tiles. ([#14958](https://github.com/mapbox/mapbox-gl-native/pull/14958))
* Fixed an issue that may cause a crash when downloading a list of `MGLOfflinePack` objects. ([#15029](https://github.com/mapbox/mapbox-gl-native/pull/15029))

### Packaging

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