Fix xray fdr mode to allow multiple flushes

[dberris]

LGTM

Thanks!

[MaskRay]

compiler-rt/test/xray/TestCases/Posix/fdr-reinit.cpp

52–55

Worth a comment why the loop exists.

compiler-rt/lib/xray/xray_fdr_logging.cpp

 XRayLogFlushStatus fdrLoggingFlush() XRAY_NEVER_INSTRUMENT {
   if (atomic_load(&LoggingStatus, memory_order_acquire) !=
       XRayLogInitStatus::XRAY_LOG_FINALIZED) {
     if (Verbosity())
       Report("Not flushing log, implementation is not finalized.\n");
     return XRayLogFlushStatus::XRAY_LOG_NOT_FLUSHING;
   }
 
-  s32 Result = XRayLogFlushStatus::XRAY_LOG_NOT_FLUSHING;
-  if (!atomic_compare_exchange_strong(&LogFlushStatus, &Result,
-                                      XRayLogFlushStatus::XRAY_LOG_FLUSHING,
-                                      memory_order_release)) {
+  if (atomic_exchange(&LogFlushStatus, XRayLogFlushStatus::XRAY_LOG_FLUSHING,
+                      memory_order_release) ==
+      XRayLogFlushStatus::XRAY_LOG_FLUSHING) {
     if (Verbosity())
-      Report("Not flushing log, implementation is still finalizing.\n");
-    return static_cast<XRayLogFlushStatus>(Result);
+      Report("Not flushing log, implementation is still flushing.\n");
+    return XRayLogFlushStatus::XRAY_LOG_NOT_FLUSHING;
   }
 
   if (BQ == nullptr) {
     if (Verbosity())
       Report("Cannot flush when global buffer queue is null.\n");
     return XRayLogFlushStatus::XRAY_LOG_NOT_FLUSHING;
   }
 

compiler-rt/test/xray/TestCases/Posix/fdr-reinit.cpp

int main(int argc, char *argv[]) {
   // Then immediately finalize the implementation.
   auto finalize_status = __xray_log_finalize();
   assert(finalize_status == XRayLogInitStatus::XRAY_LOG_FINALIZED);
 
   // Once we're here, we should then flush.
   auto flush_status = __xray_log_flushLog();
   assert(flush_status == XRayLogFlushStatus::XRAY_LOG_FLUSHED);
 
+  for (auto trial = 0; trial < 3; trial++) {
     // Without doing anything else, we should re-initialize.
     init_status = __xray_log_init_mode("xray-fdr", kConfig);
     assert(init_status == XRayLogInitStatus::XRAY_LOG_INITIALIZED);
 
     // Then we spin for a bit again calling func() enough times.
     for (auto i = 0; i < 1 << 20; ++i)
       func();
 
     // Then immediately finalize the implementation.
     finalize_status = __xray_log_finalize();
     assert(finalize_status == XRayLogInitStatus::XRAY_LOG_FINALIZED);
 
     // Once we're here, we should then flush.
     flush_status = __xray_log_flushLog();
     assert(flush_status == XRayLogFlushStatus::XRAY_LOG_FLUSHED);
+  }
 
   // Finally, we should signal the sibling thread to stop.
   keep_going.clear(std::memory_order_release);
 
   // Then join.
   t.join();
 }