fix race condition in init context (#238)

There is still a race condition on the init context. This occurs only in the event of a timeout. The goroutine actually continues executing, except we just unblock the main process (similar to js promise.race). So there is a race condition when writing to `context.Error` (1. in the timeout handler, 2. during `client.init`)
To solve, use a mutex lock and clone to context. (Cloning is necessary because even if we use a mutex lock, there is no guarantee that "Timed out" will be the final error set)

client.go

@@ -69,8 +69,9 @@ func newClientImpl(sdkKey string, options *Options) (*Client, *initContext) {
 			Logger().LogStep(StatsigProcessInitialize, "Timed out")
 			diagnostics.initialize().overall().end().success(false).reason("timeout").mark()
 			client.initInBackground()
-			context.Error = errors.New("Timed out")
-			return client, context
+			ctx := context.copy() // Goroutines are not terminated upon timeout. Clone context to avoid race condition on setting Error
+			ctx.setError(errors.New("Timed out"))
+			return client, ctx
 		}
 	} else {
 		client.init(context)
@@ -84,8 +85,8 @@ func (c *Client) init(context *initContext) {
 	c.evaluator.initialize(context)
 	c.evaluator.store.mu.RLock()
 	defer c.evaluator.store.mu.RUnlock()
-	context.Success = c.evaluator.store.source != sourceUninitialized
-	context.Source = c.evaluator.store.source
+	context.setSuccess(c.evaluator.store.source != sourceUninitialized)
+	context.setSource(c.evaluator.store.source)
 }
 
 func (c *Client) initInBackground() {

statsig_context.go

@@ -1,6 +1,9 @@
 package statsig
 
-import "time"
+import (
+	"sync"
+	"time"
+)
 
 type errorContext struct {
 	evalContext  *evalContext
@@ -28,8 +31,38 @@ type initContext struct {
 	Success bool
 	Error   error
 	Source  EvaluationSource
+	mu      sync.RWMutex
 }
 
 func newInitContext() *initContext {
 	return &initContext{Start: time.Now(), Success: false, Source: sourceUninitialized}
 }
+
+func (c *initContext) setSuccess(success bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.Success = success
+}
+
+func (c *initContext) setError(err error) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.Error = err
+}
+
+func (c *initContext) setSource(source EvaluationSource) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.Source = source
+}
+
+func (c *initContext) copy() *initContext {
+	c.mu.RLock()
+	defer c.mu.RUnlock()
+	return &initContext{
+		Start:   c.Start,
+		Success: c.Success,
+		Error:   c.Error,
+		Source:  c.Source,
+	}
+}

store.go

@@ -221,7 +221,7 @@ func (s *store) initialize(context *initContext) {
 				s.mu.Unlock()
 			}
 		} else {
-			context.Error = errors.New("Failed to parse bootstrap values")
+			context.setError(errors.New("Failed to parse bootstrap values"))
 		}
 	}
 	if s.lastSyncTime == 0 {
@@ -296,7 +296,7 @@ func (s *store) fetchConfigSpecsFromAdapter(context *initContext) {
 			dataAdapterError := DataAdapterError{Err: toError(err), Method: "get"}
 			Logger().LogError(dataAdapterError)
 			if context != nil {
-				context.Error = &dataAdapterError
+				context.setError(&dataAdapterError)
 			}
 		}
 	}()
@@ -332,7 +332,7 @@ func (s *store) handleSyncError(err error, context *initContext) {
 		Logger().LogError(fmt.Sprintf("Failed to initialize from the network. " +
 			"See https://docs.statsig.com/messages/serverSDKConnection for more information\n"))
 		s.errorBoundary.logException(err)
-		context.Error = err
+		context.setError(err)
 	} else if failDuration > syncOutdatedMax {
 		Logger().LogError(fmt.Sprintf("Syncing the server SDK with Statsig network has failed for %dms. "+
 			"Your sdk will continue to serve gate/config/experiment definitions as of the last successful sync. "+
@@ -368,7 +368,7 @@ func (s *store) fetchConfigSpecsFromServer(context *initContext) {
 		}
 	} else {
 		if context != nil {
-			context.Error = errors.New("Failed to parse config specs")
+			context.setError(errors.New("Failed to parse config specs"))
 		}
 	}
 }