Add mutex sync to SessionFlusher aggregates

CHANGELOG.md

@@ -17,6 +17,8 @@
 - Fix `send_default_pii` handling in rails controller spans [#2443](https://github.com/getsentry/sentry-ruby/pull/2443)
   - Fixes [#2438](https://github.com/getsentry/sentry-ruby/issues/2438)
 - Fix `RescuedExceptionInterceptor` to handle an empty configuration [#2428](https://github.com/getsentry/sentry-ruby/pull/2428)
+- Add mutex sync to `SessionFlusher` aggregates [#2469](https://github.com/getsentry/sentry-ruby/pull/2469)
+  - Fixes [#2468](https://github.com/getsentry/sentry-ruby/issues/2468)
 
 ## 5.21.0
 

sentry-ruby/lib/sentry/session_flusher.rb

@@ -10,6 +10,7 @@
       @pending_aggregates = {}
       @release = configuration.release
       @environment = configuration.environment
+      @mutex = Mutex.new
 
       log_debug("[Sessions] Sessions won't be captured without a valid release") unless @release
     end
@@ -18,7 +19,6 @@
       return if @pending_aggregates.empty?
 
       @client.capture_envelope(pending_envelope)
-      @pending_aggregates = {}
     end
 
     alias_method :run, :flush
@@ -42,11 +42,15 @@
     end
 
     def pending_envelope
-      envelope = Envelope.new
+      aggregates = @mutex.synchronize do
+        aggregates = @pending_aggregates.values
+        @pending_aggregates = {}
+        aggregates
+      end
 
+      envelope = Envelope.new
       header = { type: "sessions" }
-      payload = { attrs: attrs, aggregates: @pending_aggregates.values }
-
+      payload = { attrs: attrs, aggregates: aggregates }
       envelope.add_item(header, payload)
       envelope
     end