Fix a data race for SentryId.empty (#3072)

Initialize the SentryId.empty in the class initializer to fix a data race.

CHANGELOG.md

@@ -9,6 +9,7 @@
 
 ### Fixes
 
+- Fix a data race for `SentryId.empty` (#3072)
 - Changed `Trace` serialized value of `sampled` from string to boolean (#3067)
 - Duplicated HTTP breadcrumbs (#3058)
 - Expose SentryPrivate and SentrySwiftUI schemes for cartahge clients that have `--no-use-binaries` option (#3071)

Sources/Sentry/SentryId.m

@@ -16,6 +16,16 @@ @implementation SentryId
 
 static SentryId *_empty = nil;
 
++ (void)initialize
+{
+ if (self == [SentryId class]) {
+ // Initialize the empty here instead of using a lazy load approach in the getter to avoid
+ // using a lock to prevent data races. Empty is used at a couple of places in the SDK, so
+ // potentially minimizing the memory footprint doesn't apply.
+ _empty = [[SentryId alloc] initWithUUIDString:emptyUUIDString];
+ }
+}
+
 - (instancetype)init
 {
  return [self initWithUUID:[NSUUID UUID]];
@@ -84,9 +94,6 @@ - (NSUInteger)hash
 
 + (SentryId *)empty
 {
- if (nil == _empty) {
- _empty = [[SentryId alloc] initWithUUIDString:emptyUUIDString];
- }
  return _empty;
 }
 

Tests/SentryTests/Protocol/SentryIdTests.swift

@@ -80,4 +80,10 @@ class SentryIdTests: XCTestCase {
  func testHash_IsDifferentWhenObjectsAreDifferent() {
  XCTAssertNotEqual(SentryId(uuid: UUID()).hash, SentryId(uuid: fixture.uuid).hash)
  }
+
+ func testConcurrentReadsOfEmpty() {
+ testConcurrentModifications { _ in
+ XCTAssertNotNil(SentryId.empty)
+ }
+ }
 }