Allow creating a NaClAppThread without creating a new host OS thread

src/trusted/service_runtime/nacl_app_thread.c

Index: src/trusted/service_runtime/nacl_app_thread.c
diff --git a/src/trusted/service_runtime/nacl_app_thread.c b/src/trusted/service_runtime/nacl_app_thread.c
index aecf3bc8e58fd37f2d90833aac4f845e2800becd..86bb5c1fa5ceeba511823c9b9bb85e9b8852b691 100644
--- a/src/trusted/service_runtime/nacl_app_thread.c
+++ b/src/trusted/service_runtime/nacl_app_thread.c
@@ -7,6 +7,9 @@
 /*
  * NaCl Server Runtime user thread state.
  */
+
+#include <string.h>
+
 #include "native_client/src/shared/platform/aligned_malloc.h"
 #include "native_client/src/shared/platform/nacl_check.h"
 #include "native_client/src/shared/platform/nacl_exit.h"
@@ -21,10 +24,10 @@
 #include "native_client/src/trusted/service_runtime/nacl_syscall_common.h"
 
 
-void WINAPI NaClThreadLauncher(void *state) {
+void WINAPI NaClAppThreadLauncher(void *state) {
   struct NaClAppThread *natp = (struct NaClAppThread *) state;
   uint32_t thread_idx;
-  NaClLog(4, "NaClThreadLauncher: entered\n");
+  NaClLog(4, "NaClAppThreadLauncher: entered\n");
 
   NaClSignalStackRegister(natp->signal_stack);
 
@@ -141,7 +144,6 @@ struct NaClAppThread *NaClAppThreadMake(struct NaClApp *nap,
                                         uint32_t       user_tls1,
                                         uint32_t       user_tls2) {
   struct NaClAppThread *natp;
-  int rv;
   uint32_t tls_idx;
 
   natp = NaClAlignedMalloc(sizeof *natp, __alignof(struct NaClAppThread));
@@ -158,6 +160,8 @@ struct NaClAppThread *NaClAppThreadMake(struct NaClApp *nap,
    */
   natp->nap = nap;
   natp->thread_num = -1;  /* illegal index */
+  natp->host_thread_is_defined = 0;
+  memset(&natp->host_thread, 0, sizeof(natp->host_thread));
 
   /*
    * Even though we don't know what segment base/range should gs/r9/nacl_tls_idx
@@ -198,16 +202,8 @@ struct NaClAppThread *NaClAppThreadMake(struct NaClApp *nap,
   natp->fault_signal = 0;
 
   natp->dynamic_delete_generation = 0;
+  return natp;
 
-  rv = NaClThreadCtor(&natp->thread,
-                      NaClThreadLauncher,
-                      (void *) natp,
-                      NACL_KERN_STACK_SIZE);
-  if (rv != 0) {
-    return natp; /* Success */
-  }
-
-  NaClMutexDtor(&natp->suspend_mu);
  cleanup_mu:
   NaClMutexDtor(&natp->mu);
   if (NULL != natp->signal_stack) {
@@ -220,14 +216,46 @@ struct NaClAppThread *NaClAppThreadMake(struct NaClApp *nap,
 }
 
 
+int NaClAppThreadSpawn(struct NaClApp *nap,
+                       uintptr_t      usr_entry,
+                       uintptr_t      usr_stack_ptr,
+                       uint32_t       user_tls1,
+                       uint32_t       user_tls2) {
+  struct NaClAppThread *natp = NaClAppThreadMake(nap, usr_entry, usr_stack_ptr,
+                                                 user_tls1, user_tls2);
+  if (natp == NULL) {
+    return 0;
+  }
+  /*
+   * We set host_thread_is_defined assuming, for now, that
+   * NaClThreadCtor() will succeed.
+   */
+  natp->host_thread_is_defined = 1;
+  if (!NaClThreadCtor(&natp->host_thread, NaClAppThreadLauncher, (void *) natp,
+                      NACL_KERN_STACK_SIZE)) {
+    /*
+     * No other thread saw the NaClAppThread, so it is OK that
+     * host_thread was not initialized despite host_thread_is_defined
+     * being set.
+     */
+    natp->host_thread_is_defined = 0;
+    NaClAppThreadDelete(natp);
+    return 0;
+  }
+  return 1;
+}
+
+
 void NaClAppThreadDelete(struct NaClAppThread *natp) {
   /*
    * the thread must not be still running, else this crashes the system
    */
 
+  if (natp->host_thread_is_defined) {
+    NaClThreadDtor(&natp->host_thread);
+  }
   free(natp->suspended_registers);
   NaClMutexDtor(&natp->suspend_mu);
-  NaClThreadDtor(&natp->thread);
   NaClSignalStackFree(natp->signal_stack);
   natp->signal_stack = NULL;
   NaClTlsFree(natp);