Allow creating a NaClAppThread without creating a new host OS thread

src/trusted/service_runtime/osx/thread_suspension.c

Index: src/trusted/service_runtime/osx/thread_suspension.c
diff --git a/src/trusted/service_runtime/osx/thread_suspension.c b/src/trusted/service_runtime/osx/thread_suspension.c
index c5114407468c05fba77d4d49af982d125905b124..56db973f84e07816887f8fce25531eb2d060073a 100644
--- a/src/trusted/service_runtime/osx/thread_suspension.c
+++ b/src/trusted/service_runtime/osx/thread_suspension.c
@@ -26,6 +26,11 @@ struct NaClAppThreadSuspendedRegisters {
 #endif
 };
 
+static mach_port_t GetHostThreadPort(struct NaClAppThread *natp) {
+  CHECK(natp->host_thread_is_defined);
+  return pthread_mach_thread_np(natp->host_thread.tid);
+}
+
 void NaClAppThreadSetSuspendState(struct NaClAppThread *natp,
                                   enum NaClSuspendState old_state,
                                   enum NaClSuspendState new_state) {
@@ -54,7 +59,7 @@ void NaClUntrustedThreadSuspend(struct NaClAppThread *natp,
   if (natp->suspend_state == NACL_APP_THREAD_UNTRUSTED) {
     kern_return_t result;
     mach_msg_type_number_t size;
-    mach_port_t thread_port = pthread_mach_thread_np(natp->thread.tid);
+    mach_port_t thread_port = GetHostThreadPort(natp);
 
     result = thread_suspend(thread_port);
     if (result != KERN_SUCCESS) {
@@ -88,8 +93,7 @@ void NaClUntrustedThreadSuspend(struct NaClAppThread *natp,
 
 void NaClUntrustedThreadResume(struct NaClAppThread *natp) {
   if (natp->suspend_state == NACL_APP_THREAD_UNTRUSTED) {
-    mach_port_t thread_port = pthread_mach_thread_np(natp->thread.tid);
-    kern_return_t result = thread_resume(thread_port);
+    kern_return_t result = thread_resume(GetHostThreadPort(natp));
     if (result != KERN_SUCCESS) {
       NaClLog(LOG_FATAL, "NaClUntrustedThreadResume: "
               "thread_resume() call failed: error %d\n", (int) result);
@@ -138,7 +142,6 @@ void NaClAppThreadGetSuspendedRegistersInternal(
 
 void NaClAppThreadSetSuspendedRegistersInternal(
     struct NaClAppThread *natp, const struct NaClSignalContext *regs) {
-  mach_port_t thread_port = pthread_mach_thread_np(natp->thread.tid);
   kern_return_t result;
   mach_msg_type_number_t size;
   struct NaClAppThreadSuspendedRegisters *state = natp->suspended_registers;
@@ -168,7 +171,7 @@ void NaClAppThreadSetSuspendedRegistersInternal(
 #endif
 
   size = sizeof(context_copy) / sizeof(natural_t);
-  result = thread_set_state(thread_port, x86_THREAD_STATE,
+  result = thread_set_state(GetHostThreadPort(natp), x86_THREAD_STATE,
                             (void *) &context_copy, size);
   if (result != KERN_SUCCESS) {
     NaClLog(LOG_FATAL, "NaClAppThreadSetSuspendedRegistersInternal: "
@@ -177,7 +180,6 @@ void NaClAppThreadSetSuspendedRegistersInternal(
 }
 
 int NaClAppThreadUnblockIfFaulted(struct NaClAppThread *natp, int *signal) {
-  mach_port_t thread_port;
   kern_return_t result;
   if (natp->fault_signal == 0) {
     return 0;
@@ -190,8 +192,7 @@ int NaClAppThreadUnblockIfFaulted(struct NaClAppThread *natp, int *signal) {
    * undoes the effect of mach_exception_handler.c's thread_suspend()
    * call.
    */
-  thread_port = pthread_mach_thread_np(natp->thread.tid);
-  result = thread_resume(thread_port);
+  result = thread_resume(GetHostThreadPort(natp));
   if (result != KERN_SUCCESS) {
     NaClLog(LOG_FATAL, "NaClAppThreadUnblockIfFaulted: "
             "thread_resume() call failed: error %d\n", (int) result);