[libcxx-commits] [libcxxabi] 58f3243 - [libc++abi] Add a rate limiter when logging dynamic_cast errors

[Louis Dionne via libcxx-commits]

Author: Louis Dionne
Date: 2020-04-21T15:27:33-04:00
New Revision: 58f32435e8bf8e32c4e2fbe7ffa866ffc52fab13

URL: https://github.com/llvm/llvm-project/commit/58f32435e8bf8e32c4e2fbe7ffa866ffc52fab13
DIFF: https://github.com/llvm/llvm-project/commit/58f32435e8bf8e32c4e2fbe7ffa866ffc52fab13.diff

LOG: [libc++abi] Add a rate limiter when logging dynamic_cast errors

This upstreams a fix that Howard made a long time ago, where so many
errors would be logged that applications were becoming sluggish. With
this patch, the first three errors will be printed, and after that the
printing frequency decreases exponentially.

_LIBCXX_DYNAMIC_FALLBACK is only enabled on Apple platforms, so this
should be NFC for other platforms.

rdar://14996273

Differential Revision: https://reviews.llvm.org/D78330

Added: 
    

Modified: 
    libcxxabi/src/private_typeinfo.cpp

Removed: 
    


################################################################################
diff  --git a/libcxxabi/src/private_typeinfo.cpp b/libcxxabi/src/private_typeinfo.cpp
index 5ce762a22bc4..898cfaef7527 100644
--- a/libcxxabi/src/private_typeinfo.cpp
+++ b/libcxxabi/src/private_typeinfo.cpp
@@ -46,6 +46,7 @@
 #ifdef _LIBCXX_DYNAMIC_FALLBACK
 #include "abort_message.h"
 #include <sys/syslog.h>
+#include <atomic>
 #endif
 
 static inline
@@ -640,9 +641,12 @@ __dynamic_cast(const void *static_ptr, const __class_type_info *static_type,
         {
             // We get here only if there is some kind of visibility problem
             //   in client code.
-            syslog(LOG_ERR, "dynamic_cast error 1: Both of the following type_info's "
-                    "should have public visibility. At least one of them is hidden. %s"
-                    ", %s.\n", static_type->name(), dynamic_type->name());
+            static std::atomic<size_t> error_count(0);
+            size_t error_count_snapshot = error_count.fetch_add(1, std::memory_order_relaxed);
+            if ((error_count_snapshot & (error_count_snapshot-1)) == 0)
+                syslog(LOG_ERR, "dynamic_cast error 1: Both of the following type_info's "
+                        "should have public visibility. At least one of them is hidden. %s"
+                        ", %s.\n", static_type->name(), dynamic_type->name());
             // Redo the search comparing type_info's using strcmp
             info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
             info.number_of_dst_type = 1;
@@ -663,11 +667,14 @@ __dynamic_cast(const void *static_ptr, const __class_type_info *static_type,
         if (info.path_dst_ptr_to_static_ptr == unknown &&
             info.path_dynamic_ptr_to_static_ptr == unknown)
         {
-            syslog(LOG_ERR, "dynamic_cast error 2: One or more of the following type_info's "
-                            "has hidden visibility or is defined in more than one translation "
-                            "unit. They should all have public visibility. "
-                            "%s, %s, %s.\n", static_type->name(), dynamic_type->name(),
-                    dst_type->name());
+            static std::atomic<size_t> error_count(0);
+            size_t error_count_snapshot = error_count.fetch_add(1, std::memory_order_relaxed);
+            if ((error_count_snapshot & (error_count_snapshot-1)) == 0)
+                syslog(LOG_ERR, "dynamic_cast error 2: One or more of the following type_info's "
+                                "has hidden visibility or is defined in more than one translation "
+                                "unit. They should all have public visibility. "
+                                "%s, %s, %s.\n", static_type->name(), dynamic_type->name(),
+                        dst_type->name());
             // Redo the search comparing type_info's using strcmp
             info = {dst_type, static_ptr, static_type, src2dst_offset, 0};
             dynamic_type->search_below_dst(&info, dynamic_ptr, public_path, true);