Disable the profiler when a debugger is attached

runtime/vm/thread_interrupter_macos.cc

Index: runtime/vm/thread_interrupter_macos.cc
diff --git a/runtime/vm/thread_interrupter_macos.cc b/runtime/vm/thread_interrupter_macos.cc
index fb9e145f019fd5a565fb56858176a437879093ba..e37580d0e5ead5bb6c2c3151971cd6fa624500e6 100644
--- a/runtime/vm/thread_interrupter_macos.cc
+++ b/runtime/vm/thread_interrupter_macos.cc
@@ -6,6 +6,11 @@
 #if defined(TARGET_OS_MACOS)
 
 #include <errno.h>  // NOLINT
+#include <assert.h>      // NOLINT
+#include <stdbool.h>     // NOLINT
+#include <sys/types.h>   // NOLINT
+#include <unistd.h>      // NOLINT
+#include <sys/sysctl.h>  // NOLINT
 
 #include "vm/flags.h"
 #include "vm/os.h"
@@ -20,6 +25,27 @@ namespace dart {
 DECLARE_FLAG(bool, thread_interrupter);
 DECLARE_FLAG(bool, trace_thread_interrupter);
 
+// Returns true if the current process is being debugged (either
+// running under the debugger or has a debugger attached post facto).
+// Code from https://developer.apple.com/library/content/qa/qa1361/_index.html
+bool ThreadInterrupter::IsDebuggerAttached() {
+  struct kinfo_proc info;
+  // Initialize the flags so that, if sysctl fails for some bizarre
+  // reason, we get a predictable result.
+  info.kp_proc.p_flag = 0;
+  // Initialize mib, which tells sysctl the info we want, in this case
+  // we're looking for information about a specific process ID.
+  int mib[4] = {CTL_KERN, KERN_PROC, KERN_PROC_PID, getpid()};
+  size_t size = sizeof(info);
+
+  // Call sysctl.
+  size = sizeof(info);
+  int junk = sysctl(mib, sizeof(mib) / sizeof(*mib), &info, &size, NULL, 0);
+  ASSERT(junk == 0);
+  // We're being debugged if the P_TRACED flag is set.
+  return ((info.kp_proc.p_flag & P_TRACED) != 0);
+}
+
 class ThreadInterrupterMacOS : public AllStatic {
  public:
   static void ThreadInterruptSignalHandler(int signal,
@@ -48,7 +74,7 @@ class ThreadInterrupterMacOS : public AllStatic {
 
 void ThreadInterrupter::InterruptThread(OSThread* thread) {
   if (FLAG_trace_thread_interrupter) {
-    OS::Print("ThreadInterrupter interrupting %p\n", thread->id());
+    OS::PrintErr("ThreadInterrupter interrupting %p\n", thread->id());
   }
   int result = pthread_kill(thread->id(), SIGPROF);
   ASSERT((result == 0) || (result == ESRCH));