src: add PrintLibuvHandleInformation debug helper

This function is not only helpful for debugging crashes,
but can also be used as an ad-hoc debugging statement.

PR-URL: #25905
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: addaleax

src/debug_utils.cc

@@ -282,20 +282,36 @@ void DumpBacktrace(FILE* fp) {
 void CheckedUvLoopClose(uv_loop_t* loop) {
   if (uv_loop_close(loop) == 0) return;
 
-  auto sym_ctx = NativeSymbolDebuggingContext::New();
+  PrintLibuvHandleInformation(loop, stderr);
+
+  fflush(stderr);
+  // Finally, abort.
+  CHECK(0 && "uv_loop_close() while having open handles");
+}
 
-  fprintf(stderr, "uv loop at [%p] has active handles\n", loop);
+void PrintLibuvHandleInformation(uv_loop_t* loop, FILE* stream) {
+  struct Info {
+    std::unique_ptr<NativeSymbolDebuggingContext> ctx;
+    FILE* stream;
+  };
+
+  Info info { NativeSymbolDebuggingContext::New(), stream };
+
+  fprintf(stream, "uv loop at [%p] has %d active handles\n",
+          loop, loop->active_handles);
 
   uv_walk(loop, [](uv_handle_t* handle, void* arg) {
-    auto sym_ctx = static_cast<NativeSymbolDebuggingContext*>(arg);
+    Info* info = static_cast<Info*>(arg);
+    NativeSymbolDebuggingContext* sym_ctx = info->ctx.get();
+    FILE* stream = info->stream;
 
-    fprintf(stderr, "[%p] %s\n", handle, uv_handle_type_name(handle->type));
+    fprintf(stream, "[%p] %s\n", handle, uv_handle_type_name(handle->type));
 
     void* close_cb = reinterpret_cast<void*>(handle->close_cb);
-    fprintf(stderr, "\tClose callback: %p %s\n",
+    fprintf(stream, "\tClose callback: %p %s\n",
         close_cb, sym_ctx->LookupSymbol(close_cb).Display().c_str());
 
-    fprintf(stderr, "\tData: %p %s\n",
+    fprintf(stream, "\tData: %p %s\n",
         handle->data, sym_ctx->LookupSymbol(handle->data).Display().c_str());
 
     // We are also interested in the first field of what `handle->data`
@@ -309,14 +325,10 @@ void CheckedUvLoopClose(uv_loop_t* loop) {
       first_field = *reinterpret_cast<void**>(handle->data);
 
     if (first_field != nullptr) {
-      fprintf(stderr, "\t(First field): %p %s\n",
+      fprintf(stream, "\t(First field): %p %s\n",
           first_field, sym_ctx->LookupSymbol(first_field).Display().c_str());
     }
-  }, sym_ctx.get());
-
-  fflush(stderr);
-  // Finally, abort.
-  CHECK(0 && "uv_loop_close() while having open handles");
+  }, &info);
 }
 
 std::vector<std::string> NativeSymbolDebuggingContext::GetLoadedLibraries() {

src/debug_utils.h

@@ -119,6 +119,7 @@ class NativeSymbolDebuggingContext {
 // about giving information on currently existing handles, if there are any,
 // but still aborts the process.
 void CheckedUvLoopClose(uv_loop_t* loop);
+void PrintLibuvHandleInformation(uv_loop_t* loop, FILE* stream);
 
 }  // namespace node
 

test/abort/test-addon-uv-handle-leak.js

@@ -89,7 +89,7 @@ if (process.argv[2] === 'child') {
 
     switch (state) {
       case 'initial':
-        assert(/^uv loop at \[.+\] has active handles$/.test(line), line);
+        assert(/^uv loop at \[.+\] has \d+ active handles$/.test(line), line);
         state = 'handle-start';
         break;
       case 'handle-start':