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Ensure no redundant rcl_logging initialization and finalization. #560

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Ensure no redundant rcl_logging initialization and finalization. #560

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2a141c2
Merge remote-tracking branch 'upstream/master'
fujitatomoya Jan 23, 2020
6602f6c
Avoid redundant rcl_logging initialization and finalization.
fujitatomoya Jan 23, 2020
1bf89b8
use atomic counter for rcl logging init/fini.
fujitatomoya Jan 24, 2020
894e883
reconsider atomic counter with expectation logging init/fini always s…
fujitatomoya Jan 28, 2020
3df75c1
get rid of unnecessary difference and change name for global variable.
fujitatomoya Feb 3, 2020
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15 changes: 10 additions & 5 deletions rcl/src/rcl/logging.c
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Original file line number Diff line number Diff line change
Expand Up @@ -71,7 +71,9 @@ rcl_logging_init(const rcl_arguments_t * global_args, const rcl_allocator_t * al
{
RCL_CHECK_ARGUMENT_FOR_NULL(global_args, RCL_RET_INVALID_ARGUMENT);
RCL_CHECK_ARGUMENT_FOR_NULL(allocator, RCL_RET_INVALID_ARGUMENT);

if (rcutils_atomic_fetch_add_uint64_t(&__rcl_logging_init_count, 1)) {
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Why are we counting and not just using a flag? This function is marked as not thread-safe, and rcl_logging_fini as well. So we don't have to handle the case where this is called multiple times concurrently. It's up to the code above this to ensure it isn't called in a thread unsafe way.

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Ok, I see why a counter, but why atomic?

return RCL_RET_OK;
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I wonder if we should log something here, to not return silently.
Maybe, an user might expect to be able to configure a logging of two contexts differently.

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okay, that is one of the cases, let's add it to notify the user.

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I agree, but instead I'd prefer for this to fail instead (return an error code). That way the caller can decide how to react to this. As-is the caller cannot tell if the function succeeded or "succeeded" but didn't use the given settings.

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In fact, I think the better solution would look like this (from the caller side):

Context::Context(...)
{
  // ...
  std::lock_guard<std::mutex> lock(g_logging_mutex);  // ensures thread-safety
  if (rcl_logging_is_initialized()) {
    auto ret = rcl_logging_init(...);
    if (ret != RCL_RET_OK) {
      // error handling
    }
  } else {
    auto ret = rcl_logging_increase_ref_count();  // safe because of lock above
    if (ret != RCL_RET_OK) {
      // error handling
    }
  }
  // ...
}

Context::~Context()
{
  // ...
  std::lock_guard<std::mutex> lock(g_logging_mutex);  // ensures thread-safety
  auto ret = rcl_logging_decrease_ref_count();  // will implicitly fini() if ref_count is zero
  if (ret != RCL_RET_OK) {
    // error handling
  }
  // ...
}

So that it is more explicit what's happening.

Or in the case where something is using logging but doesn't have what is required to initialize it (requires something else initialized it first):

{
  // ...
  std::lock_guard<std::mutex> lock(g_logging_mutex);  // ensures thread-safety
  if (rcl_logging_increase_ref_count() == RCL_LOGGING_NOT_INITIALIZED) {
    // error handling because it was unexpectedly not initialized...
  }
  // ...
}

Not sure there's a use case for the second example, but either way I think having init return OK but not actually consider the input arguments is probably not good. But at the same time you need to see if it is initialized and increase the reference count some how.

Also, out of scope for this pr, but logging should probably not require the use of global... This is only a problem because we're mapping non-globals (multiple context) to the initialization of a global. If each context could create its own logging instance this would not be a problem.

}
RCUTILS_LOGGING_AUTOINIT
g_logging_allocator = *allocator;
int default_level = global_args->impl->log_level;
Expand All @@ -81,7 +83,6 @@ rcl_logging_init(const rcl_arguments_t * global_args, const rcl_allocator_t * al
g_rcl_logging_ext_lib_enabled = !global_args->impl->log_ext_lib_disabled;
rcl_ret_t status = RCL_RET_OK;
g_rcl_logging_num_out_handlers = 0;
(void) rcutils_atomic_fetch_add_uint64_t(&__rcl_logging_init_count, 1);

if (default_level >= 0) {
rcutils_logging_set_default_logger_level(default_level);
Expand Down Expand Up @@ -112,10 +113,14 @@ rcl_logging_init(const rcl_arguments_t * global_args, const rcl_allocator_t * al
rcl_ret_t rcl_logging_fini()
{
rcl_ret_t status = RCL_RET_OK;
uint64_t current_count = rcutils_atomic_fetch_add_uint64_t(&__rcl_logging_init_count, -1);

if (current_count != 1) {
return status;
if (rcutils_atomic_load_uint64_t(&__rcl_logging_init_count) > 0) {
uint64_t current_count = rcutils_atomic_fetch_add_uint64_t(&__rcl_logging_init_count, -1);
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if (current_count != 1) {
return RCL_RET_OK;
}
} else {
return RCL_RET_OK;
}

rcutils_logging_set_output_handler(rcutils_logging_console_output_handler);
Expand Down