Fix the profiler for threads spawned from the Linux eventhandler

runtime/vm/os_thread_linux.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"  // NOLINT
+#include "platform/signal_blocker.h"  // NOLINT
+
 #if defined(TARGET_OS_LINUX)
 
 #include "vm/os_thread.h"
 
 #include <errno.h>  // NOLINT
 #include <sys/resource.h>  // NOLINT
 #include <sys/syscall.h>  // NOLINT
 #include <sys/time.h>  // NOLINT
 
 #include "platform/assert.h"
@@ skipping 62 matching lines @@
 
  private:
   const char* name_;
   OSThread::ThreadStartFunction function_;
   uword parameter_;
 
   DISALLOW_COPY_AND_ASSIGN(ThreadStartData);
 };
 
 
+// Spawned threads inherit their spawner's signal mask. We sometimes spawn
+// threads for running Dart code from a thread that is blocking SIGPROF.
+// This function explicitly unblocks SIGPROF so the profiler continues to
+// sample this thread.
+static void UnblockSIGPROF() {
+  sigset_t set;
+  sigemptyset(&set);
+  sigaddset(&set, SIGPROF);
+  int r = pthread_sigmask(SIG_UNBLOCK, &set, NULL);
+  USE(r);
+  ASSERT(r == 0);
+  ASSERT(!CHECK_IS_BLOCKING(SIGPROF));
+}
+
+
 // Dispatch to the thread start function provided by the caller. This trampoline
 // is used to ensure that the thread is properly destroyed if the thread just
 // exits.
 static void* ThreadStart(void* data_ptr) {
   ThreadStartData* data = reinterpret_cast<ThreadStartData*>(data_ptr);
 
   const char* name = data->name();
   OSThread::ThreadStartFunction function = data->function();
   uword parameter = data->parameter();
   delete data;
 
   // Create new OSThread object and set as TLS for new thread.
   OSThread* thread = OSThread::CreateOSThread();
   if (thread != NULL) {
     OSThread::SetCurrent(thread);
     thread->set_name(name);
-
+    UnblockSIGPROF();
     // Call the supplied thread start function handing it its parameters.
     function(parameter);
   }
 
   return NULL;
 }
 
 
 int OSThread::Start(const char* name,
                     ThreadStartFunction function,
@@ skipping 316 matching lines @@
 void Monitor::NotifyAll() {
   // When running with assertions enabled we track the owner.
   ASSERT(IsOwnedByCurrentThread());
   int result = pthread_cond_broadcast(data_.cond());
   VALIDATE_PTHREAD_RESULT(result);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)