# Limit compiler/linker job concurrency to avoid OOMs on subtrees where compilation/linking is memory-intensive.
#
# Usage from CMake:
#    set (MAX_COMPILER_MEMORY 2000 CACHE INTERNAL "") # megabyte
#    set (MAX_LINKER_MEMORY 3500 CACHE INTERNAL "") # megabyte
#    include (cmake/limit_jobs.cmake)
#
# (bigger values mean fewer jobs)

cmake_host_system_information(RESULT TOTAL_PHYSICAL_MEMORY QUERY TOTAL_PHYSICAL_MEMORY)
cmake_host_system_information(RESULT NUMBER_OF_LOGICAL_CORES QUERY NUMBER_OF_LOGICAL_CORES)

# Set to disable the automatic job-limiting
option(PARALLEL_COMPILE_JOBS "Maximum number of concurrent compilation jobs" OFF)
option(PARALLEL_LINK_JOBS "Maximum number of concurrent link jobs" OFF)

if (NOT PARALLEL_COMPILE_JOBS AND MAX_COMPILER_MEMORY)
    math(EXPR PARALLEL_COMPILE_JOBS ${TOTAL_PHYSICAL_MEMORY}/${MAX_COMPILER_MEMORY})

    if (NOT PARALLEL_COMPILE_JOBS)
        set (PARALLEL_COMPILE_JOBS 1)
    endif ()
    if (PARALLEL_COMPILE_JOBS LESS NUMBER_OF_LOGICAL_CORES)
        message("The auto-calculated compile jobs limit (${PARALLEL_COMPILE_JOBS}) underutilizes CPU cores (${NUMBER_OF_LOGICAL_CORES}). Set PARALLEL_COMPILE_JOBS to override.")
    endif()
endif ()

if (NOT PARALLEL_LINK_JOBS AND MAX_LINKER_MEMORY)
    math(EXPR PARALLEL_LINK_JOBS ${TOTAL_PHYSICAL_MEMORY}/${MAX_LINKER_MEMORY})

    if (NOT PARALLEL_LINK_JOBS)
        set (PARALLEL_LINK_JOBS 1)
    endif ()
    if (PARALLEL_LINK_JOBS LESS NUMBER_OF_LOGICAL_CORES)
        message("The auto-calculated link jobs limit (${PARALLEL_LINK_JOBS}) underutilizes CPU cores (${NUMBER_OF_LOGICAL_CORES}). Set PARALLEL_LINK_JOBS to override.")
    endif()
endif ()

# ThinLTO provides its own parallel linking
# (which is enabled only for RELWITHDEBINFO)
#
# But use 2 parallel jobs, since:
# - this is what llvm does
# - and I've verfied that lld-11 does not use all available CPU time (in peak) while linking one binary
if (CMAKE_BUILD_TYPE_UC STREQUAL "RELWITHDEBINFO" AND ENABLE_THINLTO)
    if (ARCH_AARCH64)
        # aarch64 builds start to often fail with OOMs (reason not yet clear), for now let's limit the concurrency
        message(STATUS "ThinLTO provides its own parallel linking - limiting parallel link jobs to 1.")
        set (PARALLEL_LINK_JOBS 1)
        if (LINKER_NAME MATCHES "lld")
            math(EXPR LTO_JOBS ${NUMBER_OF_LOGICAL_CORES}/4)
            set (CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO "${CMAKE_EXE_LINKER_FLAGS_RELWITHDEBINFO} -Wl,--thinlto-jobs=${LTO_JOBS}")
        endif()
    elseif (PARALLEL_LINK_JOBS GREATER 2)
        message(STATUS "ThinLTO provides its own parallel linking - limiting parallel link jobs to 2.")
        set (PARALLEL_LINK_JOBS 2)
    endif ()
endif()

message(STATUS "Building sub-tree with ${PARALLEL_COMPILE_JOBS} compile jobs and ${PARALLEL_LINK_JOBS} linker jobs (system: ${NUMBER_OF_LOGICAL_CORES} cores, ${TOTAL_PHYSICAL_MEMORY} MB RAM, 'OFF' means the native core count).")

if (PARALLEL_COMPILE_JOBS LESS NUMBER_OF_LOGICAL_CORES)
    set(CMAKE_JOB_POOL_COMPILE compile_job_pool${CMAKE_CURRENT_SOURCE_DIR})
    string (REGEX REPLACE "[^a-zA-Z0-9]+" "_" CMAKE_JOB_POOL_COMPILE ${CMAKE_JOB_POOL_COMPILE})
    set_property(GLOBAL APPEND PROPERTY JOB_POOLS ${CMAKE_JOB_POOL_COMPILE}=${PARALLEL_COMPILE_JOBS})
endif ()

if (PARALLEL_LINK_JOBS LESS NUMBER_OF_LOGICAL_CORES)
    set(CMAKE_JOB_POOL_LINK link_job_pool${CMAKE_CURRENT_SOURCE_DIR})
    string (REGEX REPLACE "[^a-zA-Z0-9]+" "_" CMAKE_JOB_POOL_LINK ${CMAKE_JOB_POOL_LINK})
    set_property(GLOBAL APPEND PROPERTY JOB_POOLS ${CMAKE_JOB_POOL_LINK}=${PARALLEL_LINK_JOBS})
endif ()