Fix bug on the disorder of calling shutdown callback

[Barry-Xu-2018]

Address #2096

Signed-off-by: Barry Xu barry.xu@sony.com

[clalancette]

One very minor thing pointed out inline. Otherwise looks good with green CI.

[fujitatomoya]

lgtm! @Barry-Xu-2018 thanks for quick response.

[fujitatomoya]

@clalancette @alsora thanks for the review, btw can we backport this to humble?

[fujitatomoya]

CI:

• Linux
• Linux-aarch64
• Windows

[clalancette]

@clalancette @alsora thanks for the review, btw can we backport this to humble?

Hm. So unfortunately, this breaks ABI because of the change of type from std::unordered_set to std::vector. So this would not generally be eligible for backporting. We'd have to consider another non-ABI breaking way to backport this, or explicitly make an exception here.

[fujitatomoya]

• Windows

[fujitatomoya]

@clalancette if the backport is hard requirement, we would probably consider other approach. I believe that breaking ABI/API policy would be much bigger problem.

[Barry-Xu-2018]

@clalancette @fujitatomoya

In order to keep ABI compatible, we cannot add new variable (except static variable) into class Context.
Maybe use global variable as one solution, but it will make code ugly.

struct ShutdownCallback {
  std::vector<weak_ptr> pre_callback;
  std::vector<weak_ptr> on_callback;
};

static std:map<Context*, ShutdownCallback> g_shutdownCallback;
static mutex s_shutdownCallback_mutex;

Change code on adding/removing/call shutdown callback to use this global variable.

Now I not find better approach

[clalancette]

I'm going to go ahead and merge this one in, since it is an obvious improvement for Rolling. We can consider fixing Humble (either the documentation or with an ABI-compatible fix) separately.