Our Web Worker code uses a thread pool where a single OS thread can be reused
for different worker scripts during its lifetime. Before this patch, we only
registered these threads with the profiler for the duration that they're
running a worker script. So the same OS thread could be registered with the
profiler during multiple disjoint time ranges, and we would expect the profiler
to treat those different registrations as different conceptual threads.
This had multiple advantages:
- The "thread name" of the conceptual thread can include the script URL:
"DOM Worker <scriptURL>". This allowed you to create thread filter which
match a part of the URL, so you had the option of profiling just the worker
threads you were interested in.
- We wouldn't waste time sampling a worker thread while it's idle and has no
script.
But it also had disadvantages:
- The profiler platform doesn't actually know how to deal with different
"conceptual threads" that share the same OS thread. This lead to surprising
breakage in different places. For example, the contents in the profiler
buffer are marked with ThreadId entries which use the OS thread id.
- What we show in the profiler UI didn't not match reality, and might be
confusing to some people.
I don't think the advantages are large enough to warrant teaching the rest of
the profiler platform to deal with conceptual threads. So this change makes us
stop doing the special thing and just register the OS threads for their entire
duration.
MozReview-Commit-ID: 82RtlRlwy3Y
Currently the Gecko Profiler defines a moderate amount of stuff when
MOZ_GECKO_PROFILER is undefined. It also #includes various headers, including
JS ones. This is making it difficult to separate Gecko's media stack for
inclusion in Servo.
This patch greatly simplifies how things are exposed. The starting point is:
- GeckoProfiler.h can be #included unconditionally;
- everything else from the profiler must be guarded by MOZ_GECKO_PROFILER.
In practice this introduces way too many #ifdefs, so the patch loosens it by
adding no-op macros for a number of the most common operations.
The net result is that #ifdefs and macros are used a bit more, but almost
nothing is exposed in non-MOZ_GECKO_PROFILER builds (including
ProfilerMarkerPayload.h and GeckoProfiler.h), and understanding what is exposed
is much simpler than before.
Note also that in BHR, ThreadStackHelper is now entirely absent in
non-MOZ_GECKO_PROFILER builds.
XPCOM's string API doesn't have the notion of a "null string". But it does have
the notion of a "void string" (or "voided string"), and that's what these
functions are returning. So the names should reflect that.
Because we want to remove nsAdoptingString. We have other variants that don't
use nsAdoptingString, which can be used instead. There are three basic
patterns.
1. The easiest case is when we don't check for success.
> nsAdoptingString s = Preferences::GetString("foo");
> foo(s);
becomes:
> nsAutoString s;
> Preferences::GetString("foo", s);
> foo(s);
2. The next case is when we check if the result is empty.
> nsAdoptingString s = Preferences::GetString("foo");
> if (s.IsEmpty()) { ... }
becomes:
> nsAutoString s;
> Preferences::GetString("foo", s);
> if (s.IsEmpty()) { ... }
3. The final case is when we null check the result.
> nsAdoptingString s = Preferences::GetString("foo");
> if (s) { ... }
becomes:
> nsAutoString s;
> nsresult rv = Preferences::GetString("foo", s);
> if (NS_SUCCEEDED(rv)) { ... }
The patch also avoids some UTF8/UTF16 conversions in a few places.
This patch reduces the differences between builds where the profiler is enabled
and those where the profiler is disabled. It does this by removing numerous
MOZ_GECKO_PROFILER checks.
These changes have the following consequences.
- Various functions and classes are now defined in all builds, and so can be
used unconditionally: profiler_add_marker(), profiler_set_js_context(),
profiler_clear_js_context(), profiler_get_pseudo_stack(), AutoProfilerLabel.
(They are effectively no-ops in non-profiler builds, of course.)
- The no-op versions of PROFILER_* are now gone. The remaining versions are
almost no-ops when the profiler isn't built.
For the Quatum DOM project, it's better to work in terms of event targets than
threads. This patch converts DOM code to operate on event targets rather than
threads, when possible.
MozReview-Commit-ID: 5FgvpKadUA2
