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[flang-rt] Add the ability to have user supplied callback functions to further customize the runtime environment. #155646

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Merged
merged 6 commits into from
Aug 29, 2025
Merged

[flang-rt] Add the ability to have user supplied callback functions to further customize the runtime environment. #155646

merged 6 commits into from
Aug 29, 2025
+85 −1

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d-parks
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@d-parks d-parks commented Aug 27, 2025

Add the ability to have pre and post call back functions to ExecutionEnvironment::Configure() to allow further customization of the flang runtime environment (called from _FortranAStartProgam) in situations where either the desired features/functionality are proprietary or are too specific to be accepted by the flang community.

Example:
Custom constructor object linked with flang objects:

#include "flang-rt/runtime/environment.h"
#include "flang/Runtime/entry-names.h"
#include "flang/Runtime/extensions.h"

namespace Fortran::runtime {

// Do something specific to the flang runtime environment prior to the
// core logic of ExecutionEnvironment::Configure().
static void
CustomPreConfigureEnv(int argc, const char *argv[], const char *envp[],
                      const EnvironmentDefaultList *envDefaultList) {
  puts(__func__);
}

// Do something specific to the flang runtime environment after running the
// core logic of ExecutionEnvironment::Configure().
static void
CustomPostConfigureEnv(int argc, const char *argv[], const char *envp[],
                       const EnvironmentDefaultList *envDefaultList) {
  puts(__func__);
}

void __attribute__((constructor)) CustomInitCstor(void) {
  // Possibilities:
  // RTNAME(RegisterConfigureEnv)(&CustomPreConfigureEnv,
  // &CustomPostConfigureEnv); RTNAME(RegisterConfigureEnv)(nullptr,
  // &CustomPostConfigureEnv);
  RTNAME(RegisterConfigureEnv)(&CustomPreConfigureEnv, nullptr);
}
} // namespace Fortran::runtime

[flang-rt] Add the ability to have user supplied callback functions t…
b616c34 
…o further customize the runtime environment.

	modified:   flang-rt/include/flang-rt/runtime/environment.h
	modified:   flang-rt/lib/runtime/environment.cpp
@d-parks d-parks requested review from klausler and vzakhari August 27, 2025 15:59
@d-parks d-parks changed the title [flang-rt] Add the ability to have user supplied callback functions too further customize the runtime environment. [flang-rt] Add the ability to have user supplied callback functions to further customize the runtime environment. Aug 27, 2025
vzakhari
vzakhari reviewed Aug 27, 2025
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flang-rt/include/flang-rt/runtime/environment.h Outdated

// Optional callback routines to be invoked pre and post
// execution environment setup.
void (*PreConfigureEnv)(int, const char *[], const char *[],
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Thank you, Dave!

It looks good to me, except maybe we should typedef the type of the callback functions (probably within ExecutionEnvironment struct), so that we can reduce text here and in the declaration of RegisterConfigureEnv.

@klausler
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Should there be support for multiple callbacks?

David Parks added 3 commits August 27, 2025 13:57
[flang-rt] Incorporate review comment llvm#155646.
3285393 
	modified:   ../../include/flang-rt/runtime/environment.h
	modified:   environment.cpp
[flang-rt] Cleanup dead code.
5089515 
	modified:   ../../include/flang-rt/runtime/environment.h
[flang-rt] Run post environment configuration callback functions in t…
20c528a 
…he order they are registered.

	modified:   environment.cpp
klausler
klausler reviewed Aug 28, 2025
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flang-rt/lib/runtime/environment.cpp Outdated
// The pre and post callback functions are called upon entry and exit
// of ExecutionEnvironment::Configure() respectively.

void RTNAME(RegisterConfigureEnv)(
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Who's able to call this early enough to take effect?

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In the example above, the constructor will be called before _QQmain.

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Yes. Where from?

flang-rt/include/flang-rt/runtime/environment.h Outdated
// for either pre or post functions.

static constexpr int nConfigEnvCallback{8};
int nPreConfigEnvCallback{0};
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I don't think that you want to define a variable like this in a header file.

flang-rt/lib/runtime/environment.cpp Outdated
if (0 != nPreConfigEnvCallback) {
// Run an optional callback function after the core of the
// ExecutionEnvironment() logic.
for (auto i = 0; i != nPreConfigEnvCallback; ++i) {
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int i{0}; please in the runtime

flang-rt/lib/runtime/environment.cpp Outdated
if (0 != nPostConfigEnvCallback) {
// Run an optional callback function in reverse order of registration
// after the core of the ExecutionEnvironment() logic.
for (auto i = 0; i != nPostConfigEnvCallback; ++i) {
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int i{0};

David Parks added 2 commits August 28, 2025 13:18
[flang-rt] Incorporate latest review comments.
7bb8ab7 
	modified:   ../../include/flang-rt/runtime/environment.h
	modified:   environment.cpp
[flang-rt] Correct typo.
fadd662 
	modified:   environment.cpp
@d-parks d-parks merged commit f9cac5f into llvm:main Aug 29, 2025
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3 participants
@d-parks @klausler @vzakhari