Creates cpu_iphone.c

So that cpu_posix.c can be left untouched for the other platforms.

include/grpc/support/cpu.h

@@ -41,7 +41,7 @@ extern "C" {
 /* Interface providing CPU information for currently running system */
 
 /* Return the number of CPU cores on the current system. Will return 0 if
-   if information is not available. */
+   the information is not available. */
 unsigned gpr_cpu_num_cores(void);
 
 /* Return the CPU on which the current thread is executing; N.B. This should

include/grpc/support/port_platform.h

@@ -117,7 +117,11 @@
 #ifndef _BSD_SOURCE
 #define _BSD_SOURCE
 #endif
+#ifdef TARGET_OS_IPHONE
+#define GPR_CPU_IPHONE 1
+#else /* TARGET_OS_IPHONE */
 #define GPR_CPU_POSIX 1
+#endif
 #define GPR_GCC_ATOMIC 1
 #define GPR_POSIX_LOG 1
 #define GPR_POSIX_MULTIPOLL_WITH_POLL 1

src/core/support/cpu_iphone.c

@@ -0,0 +1,53 @@
+/*
+ *
+ * Copyright 2015, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#ifdef GPR_CPU_IPHONE
+
+/* Probably 2 instead of 1, but see comment on gpr_cpu_current_cpu. */
+unsigned gpr_cpu_num_cores(void) {
+  return 1;
+}
+
+/* Most code that's using this is using it to shard across work queues. So
+   unless profiling shows it's a problem or there appears a way to detect the
+   currently running CPU core, let's have it shard the default way.
+   Note that the interface in cpu.h lets gpr_cpu_num_cores return 0, but doing
+   it makes it impossible for gpr_cpu_current_cpu to satisfy its stated range,
+   and some code might be relying on it. */
+unsigned gpr_cpu_current_cpu(void) {
+  return 0;
+}
+
+#endif /* GPR_CPU_IPHONE */

src/core/support/cpu_posix.c

@@ -42,6 +42,8 @@
 #include <grpc/support/log.h>
 #include <grpc/support/sync.h>
 
+static __thread char magic_thread_local;
+
 static int ncpus = 0;
 
 static void init_ncpus() {
@@ -58,10 +60,18 @@ unsigned gpr_cpu_num_cores(void) {
   return ncpus;
 }
 
+/* This is a cheap, but good enough, pointer hash for sharding things: */
+static size_t shard_ptr(const void *info) {
+  size_t x = (size_t)info;
+  return ((x >> 4) ^ (x >> 9) ^ (x >> 14)) % gpr_cpu_num_cores();
+}
+
 unsigned gpr_cpu_current_cpu(void) {
   /* NOTE: there's no way I know to return the actual cpu index portably...
-     most code that's using this is using it to shard across work queues though */
+     most code that's using this is using it to shard across work queues though,
-  return 0;
+     so here we use thread identity instead to achieve a similar though not
+     identical effect */
+  return shard_ptr(&magic_thread_local);
 }
 
-#endif /* GPR_CPU_LINUX */
+#endif /* GPR_CPU_POSIX */