refactor a bit

Author: kevinushey

inst/NEWS

@@ -1,30 +1,38 @@
 RcppParallel 5.0.3 (UNRELEASED)
 ------------------------------------------------------------------------
+
+* setThreadOptions(...) can again be called multiple times per session.
+  The requested number of threads will be used for invocations to parallelFor()
+  and parallelReduce() that don't explicitly request a specific number of threads.
 * The parallelFor() and parallelReduce() functions gain the 'numThreads'
   argument, allowing one to limit the number of threads used for a
   particular computation.
 
 RcppParallel 5.0.2
 ------------------------------------------------------------------------
+
 * setThreadOptions(...) can now only be called once per session, to avoid
   segfaults when compiling RcppParallel / TBB with gcc 10.1. Subsequent
   calls to setThreadOptions(...) are ignored.
 
 RcppParallel 5.0.1
 ------------------------------------------------------------------------
+
 * Fixed compilation issue on OpenSUSE Tumbleweed with -flto=auto
 * Fixed compilation when CPPFLAGS = -I/usr/local/include and a version
   of libtbb is installed there
 
 RcppParallel 5.0.0
 ------------------------------------------------------------------------
+
 * RcppParallel backend can now be customized with RCPP_PARALLEL_BACKEND
   environment variable (supported values are 'tbb' and 'tinythread')
 * Fixed issue when compiling RcppParallel on macOS Catalina
 * Fixed issue when compiling RcppParallel with Rtools40
 
 RcppParallel 4.4.4
 ------------------------------------------------------------------------
+
 * Fixed an issue when compiling RcppParallel with clang-9 on Fedora
 
 RcppParallel 4.4.3

inst/include/RcppParallel.h

@@ -28,12 +28,46 @@
 
 namespace RcppParallel {
 
+namespace {
+
+template <typename T, typename U>
+int resolveValue(const char* envvar,
+                 T requestedValue,
+                 U defaultValue)
+{
+   // if the requested value is non-zero and not the default, we can use it
+   if (requestedValue != defaultValue && requestedValue > 0)
+      return requestedValue;
+   
+   // otherwise, try reading the default from associated envvar
+   // if the environment variable is unset, use the default
+   const char* var = getenv(envvar);
+   if (var == NULL)
+      return defaultValue;
+   
+   // try to convert the string to a number
+   // if an error occurs during conversion, just use default
+   errno = 0;
+   char* end;
+   long value = strtol(var, &end, 10);
+   if (errno != 0)
+      return defaultValue;
+
+   // okay, return the parsed environment variable value   
+   return value;
+}
+
+} // end anonymous namespace
+
 inline void parallelFor(std::size_t begin,
                         std::size_t end, 
                         Worker& worker,
                         std::size_t grainSize = 1,
                         int numThreads = -1)
 {
+   grainSize = resolveValue("RCPP_PARALLEL_GRAIN_SIZE", grainSize, 1);
+   numThreads = resolveValue("RCPP_PARALLEL_NUM_THREADS", numThreads, -1);
+   
 #if RCPP_PARALLEL_USE_TBB
    if (internal::backend() == internal::BACKEND_TBB)
       tbbParallelFor(begin, end, worker, grainSize, numThreads);
@@ -51,6 +85,9 @@ inline void parallelReduce(std::size_t begin,
                            std::size_t grainSize = 1,
                            int numThreads = -1)
 {
+   grainSize = resolveValue("RCPP_PARALLEL_GRAIN_SIZE", grainSize, 1);
+   numThreads = resolveValue("RCPP_PARALLEL_NUM_THREADS", numThreads, -1);
+   
 #if RCPP_PARALLEL_USE_TBB
    if (internal::backend() == internal::BACKEND_TBB)
       tbbParallelReduce(begin, end, reducer, grainSize, numThreads);
@@ -61,6 +98,6 @@ inline void parallelReduce(std::size_t begin,
 #endif
 }
 
-} // namespace RcppParallel
+} // end namespace RcppParallel
 
 #endif // __RCPP_PARALLEL__

inst/include/RcppParallel/TBB.h

@@ -178,31 +178,6 @@ class TBBArenaParallelReduceExecutor
    std::size_t end_;
    std::size_t grainSize_;
 };
-
-int tbbResolveNumThreads(int numThreads)
-{
-   // if the user has explicitly set the value away from the default,
-   // then we can just honor their request
-   if (numThreads != -1)
-      return numThreads;
-   
-   // otherwise, try reading the default from RCPP_PARALLEL_NUM_THREADS.
-   // if that is unset, we'll let tbb decide
-   const char* var = getenv("RCPP_PARALLEL_NUM_THREADS");
-   if (var == NULL)
-      return tbb::task_arena::automatic;
-   
-   // try to convert the string to a number
-   errno = 0;
-   char* end;
-   long threads = strtol(var, &end, 10);
-   
-   // if an error occurred during conversion, just use default
-   if (errno != 0)
-      threads = tbb::task_arena::automatic;
-   
-   return threads;
-}
 
 } // anonymous namespace
 
@@ -211,9 +186,9 @@ inline void tbbParallelFor(std::size_t begin,
                            std::size_t end, 
                            Worker& worker,
                            std::size_t grainSize = 1,
-                           int numThreads = -1)
+                           int numThreads = tbb::task_arena::automatic)
 {
-   tbb::task_arena arena(tbbResolveNumThreads(numThreads));
+   tbb::task_arena arena(numThreads);
    tbb::task_group group;
 
    TBBArenaParallelForExecutor executor(group, worker, begin, end, grainSize);
@@ -225,9 +200,9 @@ inline void tbbParallelReduce(std::size_t begin,
                               std::size_t end, 
                               Reducer& reducer,
                               std::size_t grainSize = 1,
-                              int numThreads = -1)
+                              int numThreads = tbb::task_arena::automatic)
 {
-   tbb::task_arena arena(tbbResolveNumThreads(numThreads));
+   tbb::task_arena arena(numThreads);
    tbb::task_group group;
 
    TBBArenaParallelReduceExecutor<Reducer> executor(group, reducer, begin, end, grainSize);