Add RcppThread::Rcerr (#60)

* add RcppThread::Rcerr

* update README.md

Author: appelmar

README.md

@@ -9,7 +9,7 @@
 Provides R-friendly threading functionality: 
 
   * thread safe versions of [Rcpp's](http://www.rcpp.org/)
-    `checkUserInterrupt()` and `Rcout`,
+    `checkUserInterrupt()`, `Rcout`, and `Rcerr`,
   * an interruptible thread class that otherwise behaves like 
    [`std::thread`](http://en.cppreference.com/w/cpp/thread/thread),
   * classes for the [thread pool
@@ -29,6 +29,8 @@ or the [API documentation](https://tnagler.github.io/RcppThread/).
 
 Since then, the following **new features** have been added:
 
+- Printing to the error stream with `Rcerr`.
+
 - Free-standing functions like `parallelFor()` now dispatch 
   to a global thread pool that persists for the entire session. This 
   significantly speeds up programs that repeatedly call these functions.
@@ -99,13 +101,14 @@ before including any headers in your source code.
 1. Add the line `CXX_STD = CXX11` to the `src/Makevars(.win)` files of your package.
 2. Add `RcppThread` to the `LinkingTo` field of your `DESCRIPTION` file.
 
-## Automatic override of `std::cout` and `std::thread`
+## Automatic override of `std::cout`, `std::cerr``, and `std::thread`
 
-There are preprocessor options to replace all occurrences of `std::cout` and 
-`std::thread` with calls to `RcppThread::Rcout` and `RcppThread::Thread` 
+There are preprocessor options to replace all occurrences of `std::cout`, `std::cerr`, and `std::thread` with calls to `RcppThread::Rcout`, `RcppThread::Rcerr`, and `RcppThread::Thread`
 (provided that the RcppThread headers are included first). To enable this, use 
+
 ```
 #define RCPPTHREAD_OVERRIDE_COUT 1    // std::cout override
+#define RCPPTHREAD_OVERRIDE_CERR 1    // std::cerr override
 #define RCPPTHREAD_OVERRIDE_THREAD 1  // std::thread override
 ```
 before including the RcppThread headers.

inst/include/RcppThread.h

@@ -8,6 +8,7 @@
 
 #include "RcppThread/RMonitor.hpp"
 #include "RcppThread/Rcout.hpp"
+#include "RcppThread/Rcerr.hpp"
 #include "RcppThread/Thread.hpp"
 #include "RcppThread/ThreadPool.hpp"
 #include "RcppThread/parallelFor.hpp"

inst/include/RcppThread/RMonitor.hpp

@@ -36,6 +36,7 @@ class RMonitor {
     // user-facing functionality must be friends, so they can access
     // protected members of RMonitor.
     friend class RPrinter;
+    friend class RErrPrinter;
     friend void checkUserInterrupt(bool condition);
     friend bool isInterrupted(bool condition);
 
@@ -100,6 +101,23 @@ class RMonitor {
         }
     }
 
+    //! prints `object` to R error stream íf called from main thread; otherwise
+    //! adds a printable version of `object` to a buffer for deferred printing.
+    //! @param object a string or coercible object to print.
+    template<class T>
+    void safelyPrintErr(const T& object)
+    {
+        std::lock_guard<std::mutex> lk(m_);
+        msgsErr_ << object;
+        if ( calledFromMainThread() && (msgsErr_.str() != std::string("")) ) {
+            // release messages in buffer
+            REprintf("%s", msgsErr_.str().c_str());
+            //R_FlushConsole();
+            // clear message buffer
+            msgsErr_.str("");
+        }
+    }
+
 private:
     //! Ctors declared private, to instantiate class use `::instance()`.
     RMonitor(void) : isInterrupted_(false) {}
@@ -119,6 +137,7 @@ class RMonitor {
 
     std::mutex m_;                           // mutex for synchronized r/w
     std::stringstream msgs_;                 // string buffer
+    std::stringstream msgsErr_;              // string buffer for stderr
     std::atomic_bool isInterrupted_;
 };
 

inst/include/RcppThread/Rcerr.hpp

@@ -0,0 +1,66 @@
+// Copyright © 2021 Thomas Nagler
+//
+// This file is part of the RcppThread and licensed under the terms of
+// the MIT license. For a copy, see the LICENSE.md file in the root directory of
+// RcppThread or https://github.com/tnagler/RcppThread/blob/master/LICENSE.md.
+
+#pragma once
+
+#include <ostream>
+#include "RcppThread/RMonitor.hpp"
+
+namespace RcppThread {
+
+//! Safely printing to the R console from threaded code.
+class RErrPrinter {
+public:
+
+    //! prints `object` to R error stream íf called from main thread; otherwise
+    //! adds a printable version of `object` to a buffer for deferred printing.
+    //! @param object a string (or coercible object) to print.
+    //! @details Declared as a friend in `RMonitor`.
+    template<class T>
+    RErrPrinter& operator<< (T& object)
+    {
+        RMonitor::instance().safelyPrintErr(object);
+        return *this;
+    }
+
+    //! prints `object` to R error stream íf called from main thread; otherwise
+    //! adds a printable version of `object` to a buffer for deferred printing.
+    //! @param object a string (or coercible object) to print.
+    //! @details Declared as a friend in `RMonitor`.
+    template<class T>
+    RErrPrinter& operator<< (const T& object)
+    {
+        RMonitor::instance().safelyPrintErr(object);
+        return *this;
+    }
+
+    //! prints `object` to R error stream íf called from main thread; otherwise
+    //! adds a printable version of `object` to a buffer for deferred printing.
+    //! @param object a string (or coercible object) to print.
+    //! @details Declared as a friend in `RMonitor`.
+    RErrPrinter& operator<< (std::ostream& (*object)(std::ostream&))
+    {
+        RMonitor::instance().safelyPrintErr(object);
+        return *this;
+    }
+};
+
+//! global `RPrinter` instance called 'Rcerr' (as in Rcpp).
+static RErrPrinter Rcerr = RErrPrinter();
+
+}
+
+// override std::cout to use RcppThread::Rcout instead
+#ifndef RCPPTHREAD_OVERRIDE_CERR
+    #define RCPPTHREAD_OVERRIDE_CERR 0
+#endif
+
+#if RCPPTHREAD_OVERRIDE_CERR
+    #define cerr RcppThreadRcerr
+    namespace std {
+        static RcppThread::RErrPrinter RcppThreadRcerr = RcppThread::RErrPrinter();
+    }
+#endif

inst/include/RcppThread/Thread.hpp

@@ -8,6 +8,7 @@
 
 #include "RcppThread/RMonitor.hpp"
 #include "RcppThread/Rcout.hpp"
+#include "RcppThread/Rcerr.hpp"
 
 #include <thread>
 #include <future>
@@ -81,13 +82,15 @@ class Thread {
         auto timeout = std::chrono::milliseconds(250);
         while (future_.wait_for(timeout) != std::future_status::ready) {
             Rcout << "";
+            Rcerr << "";
             if (isInterrupted())
                 break;
             std::this_thread::yield();
         }
         if (thread_.joinable())
             thread_.join();
         Rcout << "";
+        Rcerr << "";
         checkUserInterrupt();
     }
 

inst/include/RcppThread/ThreadPool.hpp

@@ -8,6 +8,7 @@
 
 #include "RcppThread/RMonitor.hpp"
 #include "RcppThread/Rcout.hpp"
+#include "RcppThread/Rcerr.hpp"
 #include "RcppThread/quickpool.hpp"
 
 #include <atomic>
@@ -232,10 +233,12 @@ ThreadPool::wait()
     do {
         pool_->wait(100);
         Rcout << "";
+        Rcerr << "";
         checkUserInterrupt();
 
     } while (!pool_->done());
     Rcout << "";
+    Rcerr << "";
 }
 
 //! waits for all jobs to finish.