Speed up GetRandomBytes by only entering signal-blocking scope once.

runtime/bin/crypto_linux.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 #if defined(TARGET_OS_LINUX)
 
 #include <errno.h>  // NOLINT
 #include <fcntl.h>  // NOLINT
 
 #include "bin/fdutils.h"
 #include "bin/crypto.h"
 #include "platform/signal_blocker.h"
 
 
 namespace dart {
 namespace bin {
 
 bool Crypto::GetRandomBytes(intptr_t count, uint8_t* buffer) {
-  intptr_t fd = TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY));
+  ThreadSignalBlocker signal_blocker(SIGPROF);
+  intptr_t fd = TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(
+      open("/dev/urandom", O_RDONLY));
   if (fd < 0) return false;
-  intptr_t bytes_read = FDUtils::ReadFromBlocking(fd, buffer, count);
-  VOID_TEMP_FAILURE_RETRY(close(fd));
-  return bytes_read == count;
+  intptr_t bytes_read = 0;
+  do {
+    int res = TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(
+        read(fd, buffer + bytes_read, count - bytes_read));
+    if (res < 0) {
+      int err = errno;
+      VOID_TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(close(fd));
+      errno = err;
+      return false;
+    }
+    bytes_read += res;
+  } while (bytes_read < count);
+  VOID_TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(close(fd));
+  return true;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_LINUX)