fix: don't sample events captured while handling a crash

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+**Fixes**:
+
+- Events captured while a crash is being handled, such as from the `on_crash` hook, are no longer dropped by `sample_rate`, matching the crash itself. ([#2269](https://github.com/getsentry/sentry-native/pull/2269))
+
 ## 0.17.5
 
 **Fixes**:

src/sentry_core.c

@@ -43,6 +43,9 @@ static sentry_mutex_t g_options_lock = SENTRY__MUTEX_INIT;
 #endif
 /// see sentry_get_crashed_last_run() for the possible values
 static int g_last_crash = -1;
+/// > 0 while a crash is handled; nests, e.g. inproc enters on both the
+/// crashing and the handler thread
+static volatile long g_crash_handler_depth = 0;
 
 const sentry_options_t *
 sentry__options_getref(void)
@@ -115,6 +118,8 @@ unregister_integrations(sentry_scope_t *scope, const sentry_options_t *options)
 void
 sentry__enter_crash_handler(void)
 {
+    sentry__atomic_fetch_and_add(&g_crash_handler_depth, 1);
+
     const sentry_options_t *options = g_options;
     if (options) {
         for (size_t i = 0; i < options->num_integrations; i++) {
@@ -138,6 +143,8 @@ sentry__exit_crash_handler(void)
             }
         }
     }
+
+    sentry__atomic_fetch_and_add(&g_crash_handler_depth, -1);
 }
 
 int
@@ -703,7 +710,10 @@ sentry__capture_event(
                 sentry__mutex_unlock(&mut_options->session_lock);
             }
 
-            bool should_skip = !sentry__roll_dice(options->sample_rate);
+            // events captured while handling a crash belong to the crash, which
+            // is never sampled
+            bool should_skip = sentry__atomic_fetch(&g_crash_handler_depth) == 0
+                && !sentry__roll_dice(options->sample_rate);
             if (should_skip) {
                 SENTRY_INFO("throwing away event due to sample rate");
                 sentry__client_report_discard(SENTRY_DISCARD_REASON_SAMPLE_RATE,

tests/unit/test_basic.c

@@ -122,6 +122,48 @@ SENTRY_TEST(sampling_before_send)
     TEST_CHECK_INT_EQUAL(called_beforesend, 100);
 }
 
+static void
+counting_event_transport_func(sentry_envelope_t *envelope, void *data)
+{
+    uint64_t *called = data;
+    if (!sentry_value_is_null(sentry_envelope_get_event(envelope))) {
+        *called += 1;
+    }
+    sentry_envelope_free(envelope);
+}
+
+SENTRY_TEST(sampling_crash_handler)
+{
+    uint64_t called_transport = 0;
+
+    SENTRY_TEST_OPTIONS_NEW(options);
+    sentry_options_set_dsn(options, "https://foo@sentry.invalid/42");
+    sentry_transport_t *transport
+        = sentry_transport_new(counting_event_transport_func);
+    sentry_transport_set_state(transport, &called_transport);
+    sentry_options_set_transport(options, transport);
+    sentry_options_set_sample_rate(options, 0.0);
+    sentry_init(options);
+
+    // events captured while handling a crash are not sampled, even nested
+    sentry__enter_crash_handler();
+    sentry__enter_crash_handler();
+    sentry_capture_event(
+        sentry_value_new_message_event(SENTRY_LEVEL_INFO, NULL, "foo"));
+    sentry__exit_crash_handler();
+    sentry_capture_event(
+        sentry_value_new_message_event(SENTRY_LEVEL_INFO, NULL, "foo"));
+    sentry__exit_crash_handler();
+
+    // sampling applies again once the crash handler is left
+    sentry_capture_event(
+        sentry_value_new_message_event(SENTRY_LEVEL_INFO, NULL, "foo"));
+
+    sentry_close();
+
+    TEST_CHECK_INT_EQUAL(called_transport, 2);
+}
+
 static sentry_value_t
 discarding_before_send(
     sentry_value_t event, sentry_hint_t *UNUSED(hint), void *data)

tests/unit/tests.inc

@@ -387,6 +387,7 @@ XX(rwlock_stress)
 XX(rwlock_write_blocks_reader)
 XX(rwlock_write_blocks_writer)
 XX(sampling_before_send)
+XX(sampling_crash_handler)
 XX(sampling_decision)
 XX(sampling_transaction)
 XX(scope_attachments)