436     Chrome = 6

   461     elif format == DisplayFormats.Chrome:

   462         write_to_chrome(data, fp, **kwargs)

   748 

   749 def write_to_chrome(data, fp, minthreshold=0.005, maxthreshold=0.999):

   750     samples = []

   751     laststack = collections.deque()

   752     lastseen = collections.deque()

   753 

   754     # The Chrome tracing format allows us to use a compact stack

   755     # representation to save space. It's fiddly but worth it.

   756     # We maintain a bijection between stack and ID.

   757     stack2id = {}

   758     id2stack = [] # will eventually be rendered

   759 

   760     def stackid(stack):

   761         if not stack:

   762             return

   763         if stack in stack2id:

   764             return stack2id[stack]

   765         parent = stackid(stack[1:])

   766         myid = len(stack2id)

   767         stack2id[stack] = myid

   768         id2stack.append(dict(category=stack[0][0], name='%s %s' % stack[0]))

   769         if parent is not None:

   770             id2stack[-1].update(parent=parent)

   771         return myid

   772 

   773     def endswith(a, b):

   774         return list(a)[-len(b):] == list(b)

   775 

   776     # The sampling profiler can sample multiple times without

   777     # advancing the clock, potentially causing the Chrome trace viewer

   778     # to render single-pixel columns that we cannot zoom in on.  We

   779     # work around this by pretending that zero-duration samples are a

   780     # millisecond in length.

   781 

   782     clamp = 0.001

   783 

   784     # We provide knobs that by default attempt to filter out stack

   785     # frames that are too noisy:

   786     #

   787     # * A few take almost all execution time. These are usually boring

   788     #   setup functions, giving a stack that is deep but uninformative.

   789     #

   790     # * Numerous samples take almost no time, but introduce lots of

   791     #   noisy, oft-deep "spines" into a rendered profile.

   792 

   793     blacklist = set()

   794     totaltime = data.samples[-1].time - data.samples[0].time

   795     minthreshold = totaltime * minthreshold

   796     maxthreshold = max(totaltime * maxthreshold, clamp)

   797 

   798     def poplast():

   799         oldsid = stackid(tuple(laststack))

   800         oldcat, oldfunc = laststack.popleft()

   801         oldtime, oldidx = lastseen.popleft()

   802         duration = sample.time - oldtime

   803         if minthreshold <= duration <= maxthreshold:

   804             # ensure no zero-duration events

   805             sampletime = max(oldtime + clamp, sample.time)

   806             samples.append(dict(ph='E', name=oldfunc, cat=oldcat, sf=oldsid,

   807                                 ts=sampletime*1e6, pid=0))

   808         else:

   809             blacklist.add(oldidx)

   810 

   811     # Much fiddling to synthesize correctly(ish) nested begin/end

   812     # events given only stack snapshots.

   813 

   814     for sample in data.samples:

   815         tos = sample.stack[0]

   816         name = tos.function

   817         path = simplifypath(tos.path)

   818         category = '%s:%d' % (path, tos.lineno)

   819         stack = tuple((('%s:%d' % (simplifypath(frame.path), frame.lineno),

   820                         frame.function) for frame in sample.stack))

   821         qstack = collections.deque(stack)

   822         if laststack == qstack:

   823             continue

   824         while laststack and qstack and laststack[-1] == qstack[-1]:

   825             laststack.pop()

   826             qstack.pop()

   827         while laststack:

   828             poplast()

   829         for f in reversed(qstack):

   830             lastseen.appendleft((sample.time, len(samples)))

   831             laststack.appendleft(f)

   832             path, name = f

   833             sid = stackid(tuple(laststack))

   834             samples.append(dict(ph='B', name=name, cat=path, ts=sample.time*1e6,

   835                                 sf=sid, pid=0))

   836         laststack = collections.deque(stack)

   837     while laststack:

   838         poplast()

   839     events = [s[1] for s in enumerate(samples) if s[0] not in blacklist]

   840     frames = collections.OrderedDict((str(k), v)

   841                                      for (k,v) in enumerate(id2stack))

   842     json.dump(dict(traceEvents=events, stackFrames=frames), fp, indent=1)

   843     fp.write('\n')