Add configure script to determine when -latomic is needed (#114)

* Add configure script to detect whether -latomic is needed

* Bump version and update NEWS

* Add checkbashisms

* Travis updates

Author: wch

.travis.yml

@@ -1,9 +1,16 @@
 # R for travis: see documentation at https://docs.travis-ci.com/user/languages/r
 
 language: r
-sudo: false
 cache: packages
-r:
-  - oldrel
-  - release
-  - devel
+matrix:
+  include:
+    - r: 3.2
+    - r: 3.3
+    - r: 3.4
+    - r: 3.5
+    - release
+    - devel
+addons:
+  apt:
+    packages:
+      - devscripts  # For checkbashisms in R 4.0

DESCRIPTION

@@ -1,7 +1,7 @@
 Package: later
 Type: Package
 Title: Utilities for Scheduling Functions to Execute Later with Event Loops
-Version: 1.0.0.9000
+Version: 1.0.0.9001
 Authors@R: c(
     person("Joe", "Cheng", role = c("aut", "cre"), email = "[email protected]"),
     person(family = "RStudio", role = "cph"),

NEWS.md

@@ -1,3 +1,7 @@
+## later 1.0.9001
+
+* Fixed [#73](https://github.com/r-lib/later/issues/73), [#109](https://github.com/r-lib/later/issues/109): Previously, later did not build on some platforms, notably ARM, because the `-latomic` linker was needed on those platforms. A configure script now detects when `-latomic` is needed. ([#114](https://github.com/r-lib/later/pull/114))
+
 ## later 1.0.0
 
 * Added private event loops: these are event loops that can be run independently from the global event loop. These are useful when you have code that schedules callbacks with `later()`, and you want to call `run_now()` block and wait for those callbacks to execute before continuing. Without private event loops, if you call `run_now()` to wait until a particular callback has finished, you might inadvertantly run other callbacks that were scheduled by other code. With private event loops, you can create a private loop, schedule a callback on it, then call `run_now()` on that loop until it executes, all without interfering with the global loop. ([#84](https://github.com/r-lib/later/pull/84))

cleanup

@@ -0,0 +1,2 @@
+#!/bin/sh
+rm -f src/Makevars

configure

@@ -0,0 +1,28 @@
+#!/bin/sh
+
+echo "Running configure script"
+
+# Find compiler
+CC=$("${R_HOME}"/bin/R CMD config CC)
+
+# Detect whether -latomic is needed during linking. This is needed on some
+# platforms, notably ARM (Raspberry Pi).
+echo "#include <stdint.h>
+uint64_t v;
+int main() {
+    return (int)__atomic_load_n(&v, __ATOMIC_ACQUIRE);
+}" | ${CC} -x c - -o /dev/null > /dev/null 2>&1
+
+if [ $? -eq 0 ]; then
+  echo "-latomic linker flag not needed."
+else
+  echo "-latomic linker flag needed."
+  EXTRA_PKG_LIBS=-latomic
+fi
+
+
+# Write to Makevars
+sed -e "s|@extra_pkg_libs@|$EXTRA_PKG_LIBS|" src/Makevars.in > src/Makevars
+
+# Success
+exit 0

src/Makevars renamed to src/Makevars.in

@@ -2,7 +2,7 @@
 CXX_STD=CXX11
 
 PKG_CPPFLAGS = -pthread -DSTRICT_R_HEADERS
-PKG_LIBS = -pthread
+PKG_LIBS = -pthread @extra_pkg_libs@
 
 #### Debugging flags ####
 # Uncomment to enable thread assertions