Trackers use navigator.hardwareConcurrency as yet another source of entropy to fingerprint users. The Firefox Hardware Report says 70% of Firefox users have exactly 2 cores. When the privacy.resistFingerprinting pref is set, we want to blend into the crowd so spoof navigator.hardwareConcurrency = 2 to reduce user uniqueness. This pref was added in bug 1345322 for the Tor uplift project.
https://metrics.mozilla.com/firefox-hardware-report/#goto-cpu-and-memory
MozReview-Commit-ID: CDWAaxjRpqe
NS_SetCurrentThreadName() is added as an alternative to PR_SetCurrentThreadName()
inside libxul. The thread names are collected in the form of crash annotation to
be processed on socorro.
MozReview-Commit-ID: 4RpAWzTuvPs
To run JS in separate cooperative threads, we need to split up per-thread state
from per-runtime state. This patch does that for XPConnect.
MozReview-Commit-ID: 407SlJ7nR6v
Without this change, we will call WorkerPrefChanged if a pref whose name just
_starts_ with the name of one of our WORKER_SIMPLE_PREF prefs changes. Then in
WorkerPrefChanged we will get the value of the pref that changed, and store it
under the key identified by the closure, thus writing the value of an incorrect
pref in there.
MozReview-Commit-ID: JTsvvtC5P1o
Currently, JS sampling has major problems.
- JS sampling is enabled for all JS threads from the thread that runs
locked_profiler_start() -- currently only the main thread -- but the JS
engine can't handle enabling from off-thread, and asserts. This makes
profiling workers impossible in a debug build.
- No JS thread will be JS sampled unless enableJSSampling() is called, but that
only happens in locked_profiler_start(). That means any worker threads
created while the profiler is active won't be JS sampled.
- Only the thread that runs locked_profiler_stop() -- currently only the main
thread -- ever calls disableJSSampling(). This means that worker threads that
start being JS sampled never stop being JS sampled.
This patch fixes these three problems in the following ways.
- locked_profiler_start() now sets a flag in PseudoStack that indicates
JS sampling is desired, but doesn't directly enable it. Instead, the JS
thread polls that flag and enables JS sampling itself when it sees the flag
is set. The polling is done by the interrupt callback. There was already a
flag of this sort (mJSSampling) but the new one is better.
This required adding a call to profiler_js_operation_callback() to the
InterruptCallback() in XPCJSContext.cpp. (In comparison, the
InterruptCallback() in dom/workers/RuntimeService.cpp already had such a
call.)
- RegisterCurrentThread() now requests JS sampling of a JS thread when the
profiler is active, the thread is being profiled, and JS sampling is enabled.
- locked_profiler_stop() now calls stopJSSampling() on all live threads.
The patch makes the following smaller changes as well.
- Renames profiler_js_operation_callback() as profiler_js_interrupt_callback(),
because "interrupt callback" is the standard name (viz.
JS_AddInterruptCallback()).
- Calls js::RegisterContextProfilingEventMarker() with nullptr when stopping
JS sampling, so that ProfilerJSEventMarker won't fire unnecessarily.
- Some minor formatting changes.
PseudoContext::sampleContext() is always called immediately after
profiler_get_pseudo_stack(). This patch introduces profiler_set_js_context()
and profiler_clear_js_context(), which replace the profiler_get_pseudo_stack()
+ sampleContext() pairs. This takes us a step closer to not having to export
PseudoStack outside the profiler.
There is a single GeckoSampler and it is currently only accessed on the main
thread, so it's silly to use TLS for it; a normal global variable is better.
This patch also adds main thread assertions to a number of the profiler_*()
functions. Even though bug 1330184 may get rid of some of them, right now they
are a useful as both a sanity check and documentation.
The new name makes the sense of the condition much clearer. E.g. compare:
NS_WARN_IF_FALSE(!rv.Failed());
with:
NS_WARNING_ASSERTION(!rv.Failed());
The new name also makes it clearer that it only has effect in debug builds,
because that's standard for assertions.
