Improve base::RandBytes() performance by 1.75x-2.10x on POSIX.

base/rand_util_posix.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/rand_util.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <unistd.h>
 
 #include "base/file_util.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 
 namespace {
 
 // We keep the file descriptor for /dev/urandom around so we don't need to
 // reopen it (which is expensive), and since we may not even be able to reopen
 // it if we are later put in a sandbox. This class wraps the file descriptor so
 // we can use LazyInstance to handle opening it on the first access.
 class URandomFd {
  public:
-  URandomFd() {
-    fd_ = open("/dev/urandom", O_RDONLY);
+  URandomFd() : fd_(open("/dev/urandom", O_RDONLY)) {
     DCHECK_GE(fd_, 0) << "Cannot open /dev/urandom: " << errno;
   }
 
-  ~URandomFd() {
-    close(fd_);
-  }
+  ~URandomFd() { close(fd_); }
 
   int fd() const { return fd_; }
 
  private:
-  int fd_;
+  const int fd_;
 };
 
 base::LazyInstance<URandomFd>::Leaky g_urandom_fd = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
 
 namespace base {
 
 // NOTE: This function must be cryptographically secure. http://crbug.com/140076

[wtc, 2014/01/22 22:29:09]

This comment should be in front of RandUint64(). I think this comment doesn't
make sense, but you should avoid dealing with this issue in this CL.

[DaleCurtis, 2014/01/22 22:54:14]

Done.

+void RandBytes(void* output, size_t output_length) {

[wtc, 2014/01/22 22:29:09]

Define RandBytes after RandUint64, as the Style Guide recommends.

[DaleCurtis, 2014/01/22 22:54:14]

Done.

+  const int urandom_fd = g_urandom_fd.Pointer()->fd();
+  const bool success =
+      ReadFromFD(urandom_fd, static_cast<char*>(output), output_length);
+  CHECK(success);
+}
+
 uint64 RandUint64() {
   uint64 number;
-
-  int urandom_fd = g_urandom_fd.Pointer()->fd();
-  bool success = ReadFromFD(urandom_fd, reinterpret_cast<char*>(&number),
-                            sizeof(number));
-  CHECK(success);
-
+  RandBytes(&number, sizeof(number));
   return number;
 }
 
 int GetUrandomFD(void) {
   return g_urandom_fd.Pointer()->fd();
 }
 
 }  // namespace base