Summary:
See the test for a concrete example.
We have a scenario where both a library, and a service using that library, are using fiber. Managing a separate similar-sized thread and event-base pool costs us complexity and performance. So this seems like a legit need.

The overall solution is to hash the Options struct.
But because that has some cost, I made it optional, by introducing a new FrozenOptions struct.

Reviewed By: andriigrynenko

Differential Revision: D15305274

fbshipit-source-id: 5c53d8c4ed321ae88089c64de41af8229f877d36

Summary:
This modifies the Baton data-structure to store a linked list of awaiters rather than storing a single awaiter.

When a coroutine awaits the Baton it now does a lock-free push onto a list of awaiters.

When the Baton is posted it atomically dequeues all awaiters from the list and then resumes each of them in turn.

Reviewed By: andriigrynenko

Differential Revision: D15310137

fbshipit-source-id: 895ebcf2b113fb270ad7abfedbaab68ea51de84c

Summary: [Folly] Switch from `NDEBUG` to `kIsDebug` in `MPMCQueue`, preferring C++ over the preprocessor.

Reviewed By: Orvid

Differential Revision: D15303518

fbshipit-source-id: d014cea3035527bd27854f58b1a74a48740efd20

Summary:
If the value for backoff_max is less than backoff_min, we will see inconsistent behavior where the backoff_min sleep duration is used for the first 57 attempts, then backoff_max will be used.

In our case, we hit an issue where 0 was passed for backoff_max. We would see backoff_min sleep times for the first 57 attempts, then immediately drop to 0 sleep time which led to no retry wait at all.

If backoff_max < backoff_min, there's no way to respect both, but this makes the behavior consistent across all tries.

Reviewed By: yfeldblum

Differential Revision: D15282681

fbshipit-source-id: d9dd7b2498d77e4a01c9454a639b612ed9e26519

Differential Revision:
D15177816

Original commit changeset: 7298fcdc3a73

fbshipit-source-id: fc62ec2ecf7fb06bc60cdd0c33b17b53fe35af19

Summary:
HHWheelTimer is a member of EventBase, and EventBase is passed to it in the ctor.
However during the destruction of the evb, wheel timer gets destroyed after the evb is destroyed and still retains a reference to the evb. This is not so good.

This diff fixes it by canceling the timer before the evb gets destroyed.

Reviewed By: lnicco

Differential Revision: D15177816

fbshipit-source-id: 7298fcdc3a73041484a315c420bcb866175c19cc

Summary:
This diff updates docker os_image to ubuntu18 and gcc7 in travis settings.
The dependencies that we work with internally (e.g. gcc7, boost and so on) are not present in the ubuntu-16.04. Further, the support for gcc5 is going away. So maintaining this compatibility for these platforms is painful, especially for new projects, such as mvfst.

Reviewed By: simpkins

Differential Revision: D15286181

fbshipit-source-id: eb0da9556cdb17d0aa132ac2aa4c35f9c6eccd97

Summary: [Folly] `XLOG_EVERY_N`, `XLOG_EVERY_N_EXACT`. Renaming `XLOG_EVERY_N` to `XLOG_EVERY_N_EXACT` and adding a new `XLOG_EVERY_N` which performs better under contention, at the cost of possibly missing increments and therefore over-logging.

Reviewed By: simpkins

Differential Revision: D15230953

fbshipit-source-id: cf7b86b96340f78156f7cd25f7e784b0f1b8d5fa

Summary:
[Folly] Let CPUThreadPoolExecutor use unbounded queues when no queue bounds are specified.

One constructor remains which specifies queue bounds; that constructor uses bounded queues.

Reviewed By: andriigrynenko

Differential Revision: D15113118

fbshipit-source-id: 9c8ace4f170fdfdeef152e55b371d434ad248866

Summary:
xplat folly sync got blocked due to an error with missing ::remainderl
function.
Not really sure why this function is missing, for now ignore it.

Reviewed By: Orvid

Differential Revision: D15298056

fbshipit-source-id: 34035da5de826b55e28c79b8540aacd827e1ffdf

Summary:
- On GCC 4.9 and below, the type of `vec` could not be deduced in the
  `for_each` call.
- Since folly requires GCC 5.1 or later now, which has no issues in the
  deduction, remove the workaround and associated comment.
Pull Request resolved: https://github.com/facebook/folly/pull/1126

Reviewed By: Orvid

Differential Revision: D15292875

Pulled By: yfeldblum

fbshipit-source-id: 50533536e9e73d2c3e5d466d1b6143d0d4085648

Summary: We need this for dependencies that require submodules

Reviewed By: saifhhasan, GirasoleY

Differential Revision: D15282792

fbshipit-source-id: b0cc8d645e73668252409934fd6741fb211e30ae

Summary:
On Windows, the writing operation would fail with:

```
Traceback (most recent call last):
  File ".\opensource\fbcode_builder\getdeps.py", line 400, in <module>
    sys.exit(main())
  File ".\opensource\fbcode_builder\getdeps.py", line 393, in main
    return args.func(args)
  File ".\opensource\fbcode_builder\getdeps.py", line 236, in run
    change_status = fetcher.update()
  File "C:\open\fbsource\fbcode\opensource\fbcode_builder\getdeps\fetcher.py", line 451, in update
    return mapping.mirror(self.build_options.fbsource_dir, self.repo_dir)
  File "C:\open\fbsource\fbcode\opensource\fbcode_builder\getdeps\fetcher.py", line 400, in mirror
    f.write(name + "\n")
  File "C:\Python36\lib\encodings\cp1252.py", line 19, in encode
    return codecs.charmap_encode(input,self.errors,encoding_table)[0]
UnicodeEncodeError: 'charmap' codec can't encode characters in position 104-105: character maps to <undefined>
```

and this is caused by a file in libgit2: https://github.com/libgit2/libgit2/blob/master/tests/resources/status/%E8%BF%99, which is intended to test handling non-ASCII path.

Python on Windows will write file in cp1252 encoding by default, which does not contain that Chines character. (Caveat: that file on my system doesn't have the correct file name as well, it is being encoded in IBM861 for some reason. However the characters in IBM861 does not exist in CP1252 either)

Reviewed By: wez

Differential Revision: D15281521

fbshipit-source-id: 8a75e32bc1042167c945d67e26b549fda83b6b41

Summary:
The goal is to return an error code > 127 in the case of a
transient, retryable, infrastructure error.  This diff generates
those in the case of failure in downloading a URL or from interacting
with LFS.

Reviewed By: strager

Differential Revision: D15266838

fbshipit-source-id: 4f52a791320123968869032c37912dded464a86e

Summary:
the cmake `add_test` and related functions allow specifying
the WORKING_DIRECTORY to use for tests.  We weren't respecting this
value, so this diff looks up the WORKING_DIRECTORY from the ctest
json info and adjusts the buck test info json blob that we pass
on the testpilot.

Since that interface only allows passing an argv array, we use
the `cmake -E chdir` command to run a command in a specified
directory in a portable manner.

Reviewed By: strager

Differential Revision: D15274012

fbshipit-source-id: 1f02d461d73178745794703d455494e31c2e09ed

Summary:
std::remainder isn't supplied by all platforms. Specifically, uclibc
doesn't have it. Do a similar case as with std::nextafter, i.e. implement a
folly version in case it doesn't exists.

Reviewed By: yfeldblum

Differential Revision: D15291533

fbshipit-source-id: 96a70b52af11135102fda3183626df69cdaf4261

Summary:
When building using uclibc, std::nextafter doesn't exist. This is
similar case as for android, where std::nextafter doesn't exist.
Add additional condition to choose folly supplied versions of this function.

Reviewed By: yfeldblum

Differential Revision: D15291534

fbshipit-source-id: f6c9e213248f4e2a6e88e20578aeade46dc85d6b

Summary: [Folly] Add `sorted_unique` ctor to `sorted_vector_set` and `sorted_vector_map`. The `presorted` ctors are used with presorted but not necessarily unique inputs, so uniquify the inputs in that ctors. The untagged ctors which take a backing container presort but do not uniquify the backing container, so switch to presorting and uniquifying.

Reviewed By: vitaut

Differential Revision: D15215677

fbshipit-source-id: bf920103cfb6c297c186e5389701c08218dbc4b9

Summary: [Folly] Less unneeded generality in `sorted_vector_set` and `sorted_vector_map` ctors in terms of `begin` and `end` - can just use member functions.

Reviewed By: vitaut

Differential Revision: D15215590

fbshipit-source-id: e6c8c92fdd9ae16963768b4f748aa07e9566f947

Summary: [Folly] Use `sorted_equivalent` in `TDigest` since it is less ambiguous than `presorted` and it is a backport from C++20.

Reviewed By: vitaut

Differential Revision: D15195608

fbshipit-source-id: 07bb4c7e3750affd10f182efcdf3d9ee9e4a8cf8

Summary: [Folly] Add missing comment for `TDigest::merge` overload.

Reviewed By: vitaut

Differential Revision: D15215559

fbshipit-source-id: 781105819d8160b73d6d70dc22937482f6851f4f

Summary:
[Folly] `sorted_unique_t`, `sorted_equivalent_t`, backporting from p0429 and C++20.

Note that the existing `presorted_t` is ambiguous between `sorted_unique_t` as is assumed in `sorted_vector_set` and `sorted_vector_map` and `sorted_equivalent` as is assumed in `TDigest`.

http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p0429r6.pdf

Reviewed By: Orvid

Differential Revision: D15215532

fbshipit-source-id: d90379d609088c6b306a0fc5c7db9b1ad3cdeee8

Summary:
If multiple instances of this test are running, it is possible for a
filename conflict to occur. This fixes that behavior by using a different temp
name each time.

Reviewed By: yfeldblum

Differential Revision: D15258558

fbshipit-source-id: 40e71c57e68a90bc730fb5ba427d999789f6f88c

Summary: mstch is no longer required for fbthrift, we can remove it from oss build spec

Reviewed By: vitaut

Differential Revision: D15280267

fbshipit-source-id: 5008e54af9c927f23b0d6acbf0d9beb6e004eee1

Summary: mstch is no longer required for fbthrift, we can remove it from manifests

Reviewed By: vitaut

Differential Revision: D15279652

fbshipit-source-id: 1772de7ab51fbfe048808f66290c4ca79de60608

Summary: yfeldblum says convention here is 1 or empty (or 0).

Reviewed By: yfeldblum

Differential Revision: D15271809

fbshipit-source-id: 528e4143eaa8ee86807b06c824b3d84a586ec69c

Summary: We had a rare data race on next this diff is fixing that.

Reviewed By: yfeldblum

Differential Revision: D15120382

fbshipit-source-id: d3f0e521b941fdfcd1d968a42d7e8d240c3f74e6

Summary: There's no way we can size such queues appropriately.

Reviewed By: yfeldblum

Differential Revision: D15271382

fbshipit-source-id: 7d8c5b0a3faffac3e86cb87fa18d0597facc3189

Summary: Detect at runtime whether the test runner expects skips to fail.

Reviewed By: yfeldblum

Differential Revision: D15210476

fbshipit-source-id: f1948d469b1008c85de9ed3ae93cc780caaf7f32

Summary:
Always throwing an exception in a function marked `noexcept` generates warnings that show up as errors, so just directly call `std::terminate()` instead.

Fixes https://github.com/facebook/folly/issues/1124

Reviewed By: aary

Differential Revision: D15263327

fbshipit-source-id: cf12bab76a5dc7da9414c6873fc0b0c1335691fa

Summary: This can be useful to iterate bitmasks that are ORs of power-of-2 enum flags.

Reviewed By: yfeldblum

Differential Revision: D15245333

fbshipit-source-id: 661e0bdbe4468b693e37fda12e513202a3b3ed17

Summary:
This controls whether tests are built or not.
They are not built by default.  When `--enable-tests` is turned on,
tests are enabled for the named project only, not all of the deps.
This results in a faster build, because eg: the number of tests in
folly is very large and consumers of folly don't want to spend so
much time waiting to build tests when really all they want to do
is build their own project.

Reviewed By: strager

Differential Revision: D15246336

fbshipit-source-id: 2e22fd60c983b059f71639602712087f2a188ec6

Summary:
This is needed to correctly pick up changes made to
eg: cmake.defines sections in the manifest for first-party
projects.

Reviewed By: strager

Differential Revision: D15246337

fbshipit-source-id: 35e525e885f87d6136d5ff3b94ebf34516ab947c

Summary:
Add an implicit conversion from `folly::fbstring` to `std::string_view` for
compatibility with `std::string`. Among other things this enables formatting of
`fbstring` with fmt.

Reviewed By: yfeldblum

Differential Revision: D15230438

fbshipit-source-id: 8f5a606c5e2a761cb332421130de638abfab4065

Summary: This field sets the IPV6_TCLASS attribute for the socket.

Reviewed By: yfeldblum

Differential Revision: D15240838

fbshipit-source-id: 81a14ee0a85010926b973c221184a82412975108

Summary:
Add support for AF_UNIX datagram sockets in AsyncUDPSocket class.
For UNIX sockets, the third argument to the socket() call should be 0,
and getPort() throws. Fix these instances.

Reviewed By: yfeldblum

Differential Revision: D15073543

fbshipit-source-id: 14627d256a7f15104cbc22bc4b5ce03694c90405

Summary: support for fbcode_build and travis build

Reviewed By: siyengar

Differential Revision: D15184766

fbshipit-source-id: 5117164c324d3d3c867592a88670a53b6f862477

Summary:
Taking the address of a static constexpr variable will generate undefined
references until C++17, when static constexpr variables are implicitly inline.

Turning this into a static constexpr function generates weak symbols for both
C++14 & C++17. If anything, if you don't care about this, this makes it easier
to add/remove ciphers since you no longer need to adjust the array size
in the definition in SSLOptions.cpp.

The original motivation for this change was to fix a build failure in proxygen
oss, where declaring a wangle::SSLContextConfig would lead to an undefined
symbol linker error.

Reviewed By: lnicco

Differential Revision: D15246869

fbshipit-source-id: 44c016b9eecdf999efbffdcd381c024a6ffb11ac

Summary: Propagate the executor parameter through all future callbacks to make it available at any point in the set of continuations.

Reviewed By: yfeldblum

Differential Revision: D15225264

fbshipit-source-id: 6433c9ccf8f3992fc16ebb1ea0171cc634fc3951

Summary:
[Folly] Move `co_reschedule_on_current_executor`, placing it alongside `co_current_executor`.

(Note: this ignores all push blocking failures!)

Reviewed By: lewissbaker

Differential Revision: D15227871

fbshipit-source-id: 72c125ad792ebde6bb74e288b3404116cd279cb4