From d1d3e0d0295415a9bde6499a18ad80a9b8a05bae Mon Sep 17 00:00:00 2001
From: Kyrylo Silin <silin@kyrylo.org>
Date: Wed, 26 Feb 2020 18:49:43 +0800
Subject: [PATCH] stat: synchronize `to_h` with `increment_ms`

Possibly fixes #545
(>4.4.0 <=4.13.0 causing RuntimeError: can't add a new key into hash during
iteration)
---
 CHANGELOG.md              |  2 ++
 lib/airbrake-ruby/stat.rb | 25 +++++++++++++++----------
 2 files changed, 17 insertions(+), 10 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 29d7bf3d..f68a16b2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ Airbrake Ruby Changelog
   ([#562](https://github.com/airbrake/airbrake-ruby/pull/562))
 * Fixed addition of duplicate filters on multiple `Airbrake.configure` calls
   ([#563](https://github.com/airbrake/airbrake-ruby/pull/563))
+* Improved thread-safety of `Airbrake::Stat`
+  ([#560](https://github.com/airbrake/airbrake-ruby/pull/560))
 
 ### [v4.13.2][v4.13.2] (February 21, 2020)
 
diff --git a/lib/airbrake-ruby/stat.rb b/lib/airbrake-ruby/stat.rb
index 3fe414d3..1c800f37 100644
--- a/lib/airbrake-ruby/stat.rb
+++ b/lib/airbrake-ruby/stat.rb
@@ -24,18 +24,21 @@ def initialize(sum: 0.0, sumsq: 0.0, tdigest: TDigest.new(0.05))
       @sum = sum
       @sumsq = sumsq
       @tdigest = tdigest
+      @mutex = Mutex.new
     end
 
     # @return [Hash{String=>Object}] stats as a hash with compressed TDigest
     #   (serialized as base64)
     def to_h
-      tdigest.compress!
-      {
-        'count' => tdigest.size,
-        'sum' => sum,
-        'sumsq' => sumsq,
-        'tdigest' => Base64.strict_encode64(tdigest.as_small_bytes),
-      }
+      @mutex.synchronize do
+        tdigest.compress!
+        {
+          'count' => tdigest.size,
+          'sum' => sum,
+          'sumsq' => sumsq,
+          'tdigest' => Base64.strict_encode64(tdigest.as_small_bytes),
+        }
+      end
     end
 
     # Increments tdigest timings and updates tdigest with the difference between
@@ -54,10 +57,12 @@ def increment(start_time, end_time = nil)
     # @param [Float] ms
     # @return [void]
     def increment_ms(ms)
-      self.sum += ms
-      self.sumsq += ms * ms
+      @mutex.synchronize do
+        self.sum += ms
+        self.sumsq += ms * ms
 
-      tdigest.push(ms)
+        tdigest.push(ms)
+      end
     end
 
     # We define custom inspect so that we weed out uninformative TDigest, which