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

runtime/platform/signal_blocker.h

Index: runtime/platform/signal_blocker.h
diff --git a/runtime/platform/signal_blocker.h b/runtime/platform/signal_blocker.h
index 4bfc2287a6ed4150fc77ef51cfaee82326e05cfa..356ad3632827f65b8a5267e97b35aeea37295cd6 100644
--- a/runtime/platform/signal_blocker.h
+++ b/runtime/platform/signal_blocker.h
@@ -79,6 +79,18 @@ class ThreadSignalBlocker {
 #define VOID_NO_RETRY_EXPECTED(expression)                                     \
     (static_cast<void>(NO_RETRY_EXPECTED(expression)))
 
+// 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)                       \

[Søren Gjesse, 2014/03/25 08:21:23]

It would be great if this macro could check that a ThreadSignalBlocker is in
scope.

The simple way is to just make it take a ThreadSignalBlocket reference, that it
just asserted to be not NULL in the macro.

ThreadSignalBlocker sb(...)

TEMP_FAILURE_RETRY_NO_SIGNAL_BLOCKER(&sb, ...)

It should brobably be called something like

#define TEMP_FAILURE_RETRY_WITH_SIGNAL_BLOCKER(sb, expresstion)

[Anders Johnsen, 2014/03/25 13:06:03]

I've changed it to validate in debug mode, that it's blocking SIGPROF calls.

+    ({ intptr_t __result;                                                      \
+       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_