Implement pthread_rwlock functions for NaCl newlib.

src/untrusted/pthread/pthread_types.h

 /*
  * Copyright (c) 2012 The Native Client Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
  * Native Client pthreads implementation layer
  */
 
@@ skipping 34 matching lines @@
  *       experiments with newlib as a shared library talking to glibc's ld.so.
  *       ld.so does not mind if we trample over most of its tdb structure
  *       ("tcbhead_t") as long as we keep the field "dtv" untouched and
  *       use tls_base in a compatible way (which we already do).
  */
 typedef struct {
   void *tls_base;  /* tls accesses are made relative to this base */
   void *unused_dtv;  /* increase compatibility with glibc's tcbhead_t */
   int joinable;
   int join_waiting;
+  int rdlock_count;  /* how many rdlock's does this thread hold */

[Mark Seaborn, 2015/02/02 18:29:13]

Nit: remove apostrophe.

How about writing this as a noun phrase rather than a question: "number of
rdlocks this thread holds"

Also:

 * You need to initialise this field in nc_thread.c.

 * "unsigned" would be preferred to avoid undefined behaviour in the event of an
overflow.

[Sam Clegg, 2015/02/02 19:25:08]

Done.

   nc_thread_memory_block_t *stack_node;
   nc_thread_memory_block_t *tls_node;
   nc_thread_function start_func;
   void *state;
   /*
    * irt_thread_data is used when libpthread is linked into the IRT.
    * It is used for free()ing the thread block.
    * TODO(mseaborn): This plays a similar role to tls_node; the two
    * could be unified in future.
    */
@@ skipping 28 matching lines @@
 
 static inline void *nc_memory_block_to_payload(nc_thread_memory_block_t *node) {
   return &node[1];
 }
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif  /* NATIVE_CLIENT_SRC_UNTRUSTED_PTHREAD_NC_PTHREAD_TYPES_H_ */