Fix memory leak when processing locally stored events (#334)

* Version 1.5.10

* Use autorelease pools to release allocated memory on each iteration to avoid unnecessary memory consumption.

This is necessary when working with Objective-C objects (e.g. NSData).

https://stackoverflow.com/questions/25860942/is-it-necessary-to-use-autoreleasepool-in-a-swift-program/25880106#25880106

---------

Co-authored-by: Brandon Sneed <brandon@redf.net>

Sources/Segment/Plugins/SegmentDestination.swift

@@ -160,46 +160,54 @@ extension SegmentDestination {
         guard let analytics = self.analytics else { return }
         guard let httpClient = self.httpClient else { return }
 
-        guard let files = storage.dataStore.fetch()?.dataFiles else { return }
-
-        for url in files {
-            // enter for this url we're going to kick off
-            group.enter()
-            analytics.log(message: "Processing Batch:\n\(url.lastPathComponent)")
+        // Cooperative release of allocated memory by URL instances (dataFiles).
+        autoreleasepool {
+            guard let files = storage.dataStore.fetch()?.dataFiles else { return }
 
-            // set up the task
-            let uploadTask = httpClient.startBatchUpload(writeKey: analytics.configuration.values.writeKey, batch: url) { [weak self] result in
-                defer {
-                    group.leave()
-                }
-                guard let self else { return }
-                switch result {
-                case .success(_):
-                    storage.remove(data: [url])
-                    cleanupUploads()
+            for url in files {
+                // Use the autorelease pool to ensure that unnecessary memory allocations
+                // are released after each iteration. If there is a large backlog of files
+                // to iterate, the host applications may crash due to OOM issues.
+                autoreleasepool {
+                    // enter for this url we're going to kick off
+                    group.enter()
+                    analytics.log(message: "Processing Batch:\n\(url.lastPathComponent)")
 
-                    // we don't want to retry events in a given batch when a 400
-                    // response for malformed JSON is returned
-                case .failure(Segment.HTTPClientErrors.statusCode(code: 400)):
-                    storage.remove(data: [url])
-                    cleanupUploads()
-                default:
-                    break
+                    // set up the task
+                    let uploadTask = httpClient.startBatchUpload(writeKey: analytics.configuration.values.writeKey, batch: url) { [weak self] result in
+                        defer {
+                            group.leave()
+                        }
+                        guard let self else { return }
+                        switch result {
+                        case .success(_):
+                            storage.remove(data: [url])
+                            cleanupUploads()
+
+                            // we don't want to retry events in a given batch when a 400
+                            // response for malformed JSON is returned
+                        case .failure(Segment.HTTPClientErrors.statusCode(code: 400)):
+                            storage.remove(data: [url])
+                            cleanupUploads()
+                        default:
+                            break
+                        }
+
+                        analytics.log(message: "Processed: \(url.lastPathComponent)")
+                        // the upload we have here has just finished.
+                        // make sure it gets removed and it's cleanup() called rather
+                        // than waiting on the next flush to come around.
+                        cleanupUploads()
+                    }
+
+                    // we have a legit upload in progress now, so add it to our list.
+                    if let upload = uploadTask {
+                        add(uploadTask: UploadTaskInfo(url: url, data: nil, task: upload))
+                    } else {
+                        // we couldn't get a task, so we need to leave the group or things will hang.
+                        group.leave()
+                    }
                 }
-
-                analytics.log(message: "Processed: \(url.lastPathComponent)")
-                // the upload we have here has just finished.
-                // make sure it gets removed and it's cleanup() called rather
-                // than waiting on the next flush to come around.
-                cleanupUploads()
-            }
-
-            // we have a legit upload in progress now, so add it to our list.
-            if let upload = uploadTask {
-                add(uploadTask: UploadTaskInfo(url: url, data: nil, task: upload))
-            } else {
-                // we couldn't get a task, so we need to leave the group or things will hang.
-                group.leave()
             }
         }
     }

Sources/Segment/Version.swift

@@ -15,4 +15,4 @@
 // Use release.sh's automation.
 
 // BREAKING.FEATURE.FIX
-internal let __segment_version = "1.5.9"
+internal let __segment_version = "1.5.10"