provide class for suspension of RNG synchronization (#862)

Author: kevinushey

ChangeLog

@@ -1,3 +1,9 @@
+2018-06-06  Kevin Ushey  <kevinushey@gmail.com>
+
+	* inst/include/Rcpp/RNGScope.h: Allow suspension of RNG synchronization
+	* inst/include/Rcpp/routines.h: Idem
+	* src/Rcpp_init.cpp: Idem
+	* src/api.cpp: Idem
 
 2018-06-02  Lionel Henry  <lionel@rstudio.com>
 

inst/NEWS.Rd

@@ -9,6 +9,10 @@
     \itemize{
       \item The random number \code{Generator} class no longer inhreits from
       \code{RNGScope} (Kevin in \ghpr{837} fixing \ghit{836}).
+	  \item A new class, \code{SuspendRNGSynchronizationScope}, can be created
+	  and used to ensure that calls to Rcpp functions do not attempt to call
+	  \code{::GetRNGstate()} or \code{::PutRNGstate()} for the duration of
+	  some code block.
       \item A spurious parenthesis was removed to please gcc8 (Dirk
       fixing \ghit{841})
       \item The optional \code{Timer} class header now undefines

inst/include/Rcpp/RNGScope.h

@@ -30,6 +30,12 @@ class RNGScope{
     ~RNGScope(){ internal::exitRNGScope(); }
 };
 
+class SuspendRNGSynchronizationScope {
+public:
+    SuspendRNGSynchronizationScope() { internal::beginSuspendRNGSynchronization(); }
+    ~SuspendRNGSynchronizationScope() { internal::endSuspendRNGSynchronization(); }
+};
+
 } // namespace Rcpp
 
 #endif

inst/include/Rcpp/routines.h

@@ -31,6 +31,8 @@ namespace Rcpp{
     namespace internal{
         unsigned long enterRNGScope();
         unsigned long exitRNGScope();
+        unsigned long beginSuspendRNGSynchronization();
+        unsigned long endSuspendRNGSynchronization();
         char* get_string_buffer();
         SEXP get_Rcpp_namespace();
     }
@@ -86,6 +88,18 @@ namespace Rcpp {
             return fun();
         }
 
+        inline attribute_hidden unsigned long beginSuspendRNGSynchronization(){
+            typedef unsigned long (*Fun)(void);
+            static Fun fun = GET_CALLABLE("beginSuspendRNGSynchronization");
+            return fun();
+        }
+
+        inline attribute_hidden unsigned long endSuspendRNGSynchronization(){
+            typedef unsigned long (*Fun)(void);
+            static Fun fun = GET_CALLABLE("endSuspendRNGSynchronization");
+            return fun();
+        }
+
         inline attribute_hidden char* get_string_buffer(){
             typedef char* (*Fun)(void);
             static Fun fun = GET_CALLABLE("get_string_buffer");

src/Rcpp_init.cpp

@@ -94,6 +94,8 @@ void registerFunctions(){
     RCPP_REGISTER(demangle)
     RCPP_REGISTER(enterRNGScope)
     RCPP_REGISTER(exitRNGScope)
+    RCPP_REGISTER(beginSuspendRNGSynchronization);
+    RCPP_REGISTER(endSuspendRNGSynchronization);
     RCPP_REGISTER(get_Rcpp_namespace)
     RCPP_REGISTER(get_cache)
     RCPP_REGISTER(stack_trace)

src/api.cpp

@@ -65,18 +65,34 @@ namespace Rcpp {
 
     namespace internal {
 
+        int rngSynchronizationSuspended = 0;
+
         // [[Rcpp::register]]
         unsigned long enterRNGScope() {
-            GetRNGstate();
+            if (rngSynchronizationSuspended == 0)
+                GetRNGstate();
             return 0;
         }
 
         // [[Rcpp::register]]
         unsigned long exitRNGScope() {
-            PutRNGstate();
+            if (rngSynchronizationSuspended == 0)
+                PutRNGstate();
             return 0;
         }
 
+        // [[Rcpp::register]]
+        unsigned long beginSuspendRNGSynchronization() {
+            ++rngSynchronizationSuspended;
+            return rngSynchronizationSuspended;
+        }
+
+        // [[Rcpp::register]]
+        unsigned long endSuspendRNGSynchronization() {
+            --rngSynchronizationSuspended;
+            return rngSynchronizationSuspended;
+        }
+
         // [[Rcpp::register]]
         char* get_string_buffer() {
             static char buffer[MAXELTSIZE];