[Benchmarks] Allow running multiple benchmarks at the same time

On Travis, also test the benchmarks on two cores to speed up the builds.

.travis.yml

@@ -350,7 +350,7 @@ script:
         popd
       else
         export BOOST_HANA_JUST_CHECK_BENCHMARKS=true
-        (cd build && make benchmarks)
+        (cd build && make benchmarks -j2)
       fi
     fi
 

benchmark/CMakeLists.txt

@@ -36,6 +36,8 @@ if (Meta_FOUND)
     include_directories(${Meta_INCLUDE_DIR})
 endif()
 
+boost_hana_append_flag(BOOST_HANA_HAS_FTEMPLATE_DEPTH -ftemplate-depth=-1)
+include_directories(${CMAKE_CURRENT_SOURCE_DIR})
 
 ##############################################################################
 # Configure the measure.rb script
@@ -44,30 +46,6 @@ configure_file(${CMAKE_CURRENT_SOURCE_DIR}/measure.in.rb #input
                ${CMAKE_CURRENT_BINARY_DIR}/measure.rb    #output
                @ONLY)
 
-
-##############################################################################
-# Add the special measure file and targets
-#
-# The compile.benchmark.measure target is a special target that compiles
-# the measure.cpp file and outputs compilation statistics.
-#
-# Similarly, the run.benchmark.measure target is a special target that
-# compiles the measure.cpp file, runs the resulting program and then
-# outputs execution time statistics.
-#
-# The measure.cpp file should always be left empty. The intended usage is to
-# put some code in the file, benchmark it and then put that code somewhere
-# else. In particular, note that the benchmarks added below use the measure
-# file to perform their benchmarking, and launching the benchmarks will wipe
-# anything from the `measure.cpp` file.
-##############################################################################
-boost_hana_append_flag(BOOST_HANA_HAS_FTEMPLATE_DEPTH -ftemplate-depth=-1)
-add_executable(compile.benchmark.measure EXCLUDE_FROM_ALL measure.cpp)
-set_target_properties(compile.benchmark.measure
-    PROPERTIES RULE_LAUNCH_COMPILE "${CMAKE_CURRENT_BINARY_DIR}/measure.rb")
-add_custom_target(run.benchmark.measure COMMAND compile.benchmark.measure)
-
-
 ##############################################################################
 # Add the benchmarks
 ##############################################################################
@@ -85,8 +63,15 @@ foreach(benchmark IN LISTS BOOST_HANA_BENCHMARKS)
     file(GLOB cpp_files ${directory}/*.erb.cpp)
     configure_file("${benchmark}" "${CMAKE_CURRENT_BINARY_DIR}/${target}.erb.json" @ONLY)
 
+    file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/${target}.measure.cpp "")
+    add_executable(${target}.measure EXCLUDE_FROM_ALL ${CMAKE_CURRENT_BINARY_DIR}/${target}.measure.cpp)
+    set_target_properties(${target}.measure PROPERTIES RULE_LAUNCH_COMPILE "${CMAKE_CURRENT_BINARY_DIR}/measure.rb")
+    add_custom_target(${target}.measure.run COMMAND ${target}.measure)
+
     add_custom_command(OUTPUT "${CMAKE_CURRENT_BINARY_DIR}/${target}.json"
         COMMAND ${RUBY_EXECUTABLE} -r tilt -r ${CMAKE_CURRENT_BINARY_DIR}/measure.rb
+            -e "MEASURE_FILE = '${CMAKE_CURRENT_BINARY_DIR}/${target}.measure.cpp'"
+            -e "MEASURE_TARGET = '${target}.measure'"
             -e "json = Tilt::ERBTemplate.new('${CMAKE_CURRENT_BINARY_DIR}/${target}.erb.json').render"
             -e "File.open('${CMAKE_CURRENT_BINARY_DIR}/${target}.json', 'w') { |f| f.write(json) } "
         WORKING_DIRECTORY ${directory}

benchmark/measure.in.rb

@@ -81,7 +81,7 @@ def cmake_bool(b)
 
 # aspect must be one of :compilation_time, :bloat, :execution_time
 def measure(aspect, template_relative, range)
-  measure_file = Pathname.new("@CMAKE_CURRENT_SOURCE_DIR@/measure.cpp")
+  measure_file = Pathname.new("#{MEASURE_FILE}")
   template = Pathname.new(template_relative).expand_path
   range = range.to_a
 
@@ -107,11 +107,11 @@ def measure(aspect, template_relative, range)
     # Compile the file and get timing statistics. The timing statistics
     # are output to stdout when we compile the file because of the way
     # the `compile.benchmark.measure` CMake target is setup.
-    stdout, stderr, status = make["compile.benchmark.measure"]
+    stdout, stderr, status = make["#{MEASURE_TARGET}"]
     raise "compilation error: #{stderr}\n\n#{code}" if not status.success?
     ctime = stdout.match(/\[compilation time: (.+)\]/i)
     # Size of the generated executable in KB
-    size = File.size("@CMAKE_CURRENT_BINARY_DIR@/compile.benchmark.measure").to_f / 1000
+    size = File.size("@CMAKE_CURRENT_BINARY_DIR@/#{MEASURE_TARGET}").to_f / 1000
 
     # If we didn't match anything, that's because we went too fast, CMake
     # did not have the time to see the changes to the measure file and
@@ -125,7 +125,7 @@ def measure(aspect, template_relative, range)
     # should be written to stdout by the `measure` function of the
     # `measure.hpp` header.
     if aspect == :execution_time
-      stdout, stderr, status = make["run.benchmark.measure"]
+      stdout, stderr, status = make["#{MEASURE_TARGET}.run"]
       raise "runtime error: #{stderr}\n\n#{code}" if not status.success?
       match = stdout.match(/\[execution time: (.+)\]/i)
       if match.nil?