Fix the way to count online cpus.

Read /proc/stat to count online cpus is not correct for all android
kernels. Change to reading /sys/devices/system/cpu/online instead.

Bug: 24376925
Change-Id: I3785a6c7aa15a467022a9a261b457194d688fb38

1 files changed, 53 insertions, 0 deletions

diff --git a/libc/private/get_cpu_count_from_string.h b/libc/private/get_cpu_count_from_string.h
new file mode 100644
index 000000000..a0cb95de0
--- /dev/null
+++ b/libc/private/get_cpu_count_from_string.h
@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ * 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.
+ *
+ * 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 <ctype.h>
+#include <stdlib.h>
+
+// Parse a string like: 0, 2-4, 6.
+static int GetCpuCountFromString(const char* s) {
+  int cpu_count = 0;
+  int last_cpu = -1;
+  while (*s != '\0') {
+    if (isdigit(*s)) {
+      int cpu = static_cast<int>(strtol(s, const_cast<char**>(&s), 10));
+      if (last_cpu != -1) {
+        cpu_count += cpu - last_cpu;
+      } else {
+        cpu_count++;
+      }
+      last_cpu = cpu;
+    } else {
+      if (*s == ',') {
+        last_cpu = -1;
+      }
+      s++;
+    }
+  }
+  return cpu_count;
+}