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

runtime/platform/signal_blocker.h

 // Copyright (c) 2013, 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.
 
 #ifndef PLATFORM_SIGNAL_BLOCKER_H_
 #define PLATFORM_SIGNAL_BLOCKER_H_
 
 #include "platform/globals.h"
 
 #if defined(TARGET_OS_WINDOWS)
@@ skipping 61 matching lines @@
 // This macro can be used to insert checks that a call is made, that
 // was expected to not return EINTR, but did it anyway.
 #define NO_RETRY_EXPECTED(expression)                                          \
     ({ intptr_t __result = (expression);                                       \
        ASSERT(__result != -1L || errno != EINTR);                              \
        __result; })
 
 #define VOID_NO_RETRY_EXPECTED(expression)                                     \
     (static_cast<void>(NO_RETRY_EXPECTED(expression)))
 
+// Define to check in debug mode, if a signal is currently being blocked.
+#define CHECK_IS_BLOCKING(signal)                                              \
+    ({ sigset_t signal_mask;                                                   \
+       int __r = pthread_sigmask(SIG_BLOCK, NULL, &signal_mask);               \
+       USE(__r);                                                               \
+       ASSERT(__r == 0);                                                       \
+       sigismember(&signal_mask, signal); })                                   \
+
+
+// Versions of the above, that does not enter a signal blocking scope. Use only
+// when a signal blocking scope is entered manually.
+#define TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(expression)                       \
+    ({ intptr_t __result;                                                      \
+       ASSERT(CHECK_IS_BLOCKING(SIGPROF));                                     \
+       do {                                                                    \
+         __result = (expression);                                              \
+       } while ((__result == -1L) && (errno == EINTR));                        \
+       __result; })
+
+#define VOID_TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(expression)                  \
+    (static_cast<void>(TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(expression)))
+
 }  // namespace dart
 
 #endif  // PLATFORM_SIGNAL_BLOCKER_H_