[PROF-10688] Remove a looping allocation when updating threads

ddprof-lib/src/main/cpp/profiler.cpp

@@ -36,6 +36,7 @@
 #include "vmStructs.h"
 #include "wallClock.h"
 #include <algorithm>
+#include <array>
 #include <dlfcn.h>
 #include <fstream>
 #include <memory>
@@ -996,21 +997,21 @@ void Profiler::updateJavaThreadNames() {
 }
 
 void Profiler::updateNativeThreadNames() {
-  ThreadList *thread_list = OS::listThreads();
-  for (int tid; (tid = thread_list->next()) != -1;) {
-    _thread_info.updateThreadName(
-        tid, [](int tid) -> std::unique_ptr<char[]> {
-          const size_t buffer_size = 64;
-          char *name_buf = new char[buffer_size];
-          if (OS::threadName(tid, name_buf, buffer_size)) {
-            return std::unique_ptr<char[]>(name_buf);
-          }
-          delete[] name_buf;
-          return nullptr;
-        });
-  }
+    ThreadList *thread_list = OS::listThreads();
+    constexpr size_t buffer_size = 64;
+    char name_buf[buffer_size];  // Stack-allocated buffer
+
+    for (int tid; (tid = thread_list->next()) != -1;) {
+        _thread_info.updateThreadName(
+                tid, [&](int tid) -> std::string {
+                    if (OS::threadName(tid, name_buf, buffer_size)) {
+                        return std::string(name_buf, buffer_size);
+                    }
+                    return std::string();
+                });
+    }
 
-  delete thread_list;
+    delete thread_list;
 }
 
 Engine *Profiler::selectCpuEngine(Arguments &args) {

ddprof-lib/src/main/cpp/threadInfo.cpp

@@ -67,17 +67,17 @@ int ThreadInfo::size() {
 }
 
 void ThreadInfo::updateThreadName(
-    int tid, std::function<std::unique_ptr<char[]>(int)> resolver) {
-  MutexLocker ml(_ti_lock);
+        int tid, std::function<std::string(int)> resolver) {
+    MutexLocker ml(_ti_lock);
 
-  std::map<int, std::string>::iterator it = _thread_names.lower_bound(tid);
-  if (it == _thread_names.end() || it->first != tid) {
-    std::unique_ptr<char[]> namePtr = resolver(tid);
-    if (namePtr.get() != nullptr) {
-      _thread_names.insert(it, std::map<int, std::string>::value_type(
-                                   tid, static_cast<char *>(namePtr.get())));
+    std::map<int, std::string>::iterator it = _thread_names.lower_bound(tid);
+    if (it == _thread_names.end() || it->first != tid) {
+        std::string name = resolver(tid);
+        if (!name.empty()) {
+            _thread_names.insert(it, std::map<int, std::string>::value_type(
+                    tid, std::move(name)));  // Move the string
+        }
     }
-  }
 }
 
 void ThreadInfo::reportCounters() {

ddprof-lib/src/main/cpp/threadInfo.h

@@ -22,8 +22,7 @@ class ThreadInfo {
   void set(int tid, const char *name, u64 java_thread_id);
   std::pair<std::shared_ptr<std::string>, u64> get(int tid);
 
-  void updateThreadName(int threadId,
-                        std::function<std::unique_ptr<char[]>(int)> resolver);
+  void updateThreadName(int tid, std::function<std::string(int)> resolver);
 
   int size();