Summary:
[Folly] Use a simpler atomic state in Futures `Core` v.s. `FSM` which abstracts an atomic state plus a spin-lock.

The `FSM` abstraction can be useful in more complex cases, but is not needed in the current case. All that is needed is a single barrier state, which is `Done` - setting callback and result happen before state transitions to `Done`, while invoking callback with result happens after state transitions to `Done`.

Reviewed By: marshallcline

Differential Revision: D8083703

fbshipit-source-id: 42d96b41cbdac5e7c42f3f8a661d5db3113655db

Summary:
[Folly] Use `terminate_with` in Futures `Core` invalid transitions.

Both `Promise` and `Future` check state validity before calling the `Core` transition methods and throws in invalid state. So `Core` no longer needs to throw and may terminate instead.

Reviewed By: marshallcline

Differential Revision: D8346113

fbshipit-source-id: 9ff158673149096789b29544453262797b06d441

Summary: [Folly] `folly::terminate_with`, to terminate as if by forwarding to `folly::throw_exception` but in a `noexcept` context.

Reviewed By: marshallcline

Differential Revision: D8345962

fbshipit-source-id: bc5cf5d3a3e1f085dd2989c940a6ea753a520cbf

Summary:
[Folly] Let Future check before adding a continuation whether a continuation has already been added.

Requires making wait behave more like timed-wait; alternatively, it would be possible to add a reverse state transition, but there seems not to be a need.

Reviewed By: marshallcline

Differential Revision: D8344923

fbshipit-source-id: f077fb4b83b92c96af9a83e1b1479c4cb41b048a

Summary:
[Folly] `Range` explicit conversion to any target type, with overloads enabled only for target types which are explicitly constructible from two iterators.

Also changes `Range::to` to do similar, but permits additional arguments to be forwarded as trailing arguments to the target type constructor.

For example, this makes `std::string`, `folly::fbstring`, `std::vector<char>`, and all variants with default-constructible custom allocators, to be constructible from (but not convertible from) `folly::StringPiece`.

Reviewed By: nbronson

Differential Revision: D8386240

fbshipit-source-id: 2426191d1c8ac71cd5832f784e83bbe09b8716e7

Summary:
There were two TODOs that I knew of in fbcode about this, so I decided to file
a task so we can track it.

Reviewed By: simpkins

Differential Revision: D8176921

fbshipit-source-id: 0ca45620050639659ac038dbed43acf4634f7a1d

Summary:
Added `FutureBase::delayedImplementation`. Kept the existing semantics of
`Future::delayed` and `Future::delayedUnsafe`. `SemiFuture::delayed` uses
the inline executor which means we could execute our trivial lambda on
the `Timekeeper` thread. However we ultimately return a `SemiFuture`,
so we're not necessarily on the hook to execute an arbitrarily complex
continuation.

NOTE: This is still possible if the user explicitly specifies
`.via(inline_executor)`. Perhaps we should consider disallowing, or maybe linting for this.

Reviewed By: yfeldblum

Differential Revision: D8372515

fbshipit-source-id: e660dbf2a2bb084e11c5e57d1badacf09425f939

Summary:
To implement tdigest aggregation in scuba, we need to be able to deserialize and serialize the digests.
I added a getter for the centroids so that we can serialize the tdigest, and added a constructor to create one from the list of centroids.

Last diff was reverted because of a build error :(
We were seeing an error only in opt mode because it's an error in gcc but not in clang.

Differential Revision: D8381617

fbshipit-source-id: 768a12795aeb02737eb9b060f80d01608685c91d

Summary: title

Reviewed By: yfeldblum, andriigrynenko

Differential Revision: D8386575

fbshipit-source-id: c900c8692b10004f2d9fbd95fa8ca96b3b8517d2

Summary:
[Folly] Skip trivial-copyability `Expected` expectations under gcc49.

The focus is on gcc5+; all that is needed for now is to keep code compiling with gcc49, but not necessarily to ensure optimal trivial-copyability behavior.

Reviewed By: Orvid

Differential Revision: D8364392

fbshipit-source-id: b0062193c844509b6bf26ed632dd8e5d4bdf77d2

Summary: Assume, when UBSAN is used, it is always used on top of ASAN.

Reviewed By: luciang

Differential Revision: D8360231

fbshipit-source-id: 3106cfa53567b18f199e9303ea4c14a464ff03cc

Summary: Makes a spec for libsodium.

Reviewed By: knekritz

Differential Revision: D8228801

fbshipit-source-id: 18f623bce0bbc07f711129b15b78d56b6c852bf7

Summary: [Folly] A cache for `InlineExecutor` singleton, which can be inlined into callers with little extra code compared to calling the backing function directly.

Reviewed By: marshallcline

Differential Revision: D8339793

fbshipit-source-id: d2be0128e617cfefe66809eb44ce40e1a8ae2dfb

Summary: [Folly] Write `Promise::setException` in terms of `Promise::setTry`.

Reviewed By: marshallcline

Differential Revision: D8344928

fbshipit-source-id: 90e21219f054329eca7ae1a6c2ca731a16328b6f

Revert D8360404: [folly] Support constructing TDigest from centroids and getting centroids from TDigest

Differential Revision:
D8360404

Original commit changeset: b0f42e892f66

fbshipit-source-id: 985ba55bb443aafe7c324f15caeca0abb34d200a

Summary: Before this diff, since `ctx->memo_` starts out in the `OnlyResult` state, the first reduce (and therefore all subsequent reduces) are run immediately inside the lock.

Reviewed By: yfeldblum

Differential Revision: D8319067

fbshipit-source-id: 5ed08885beefb42c6efb61768fcbc36e0a08a46b

Summary:
To implement tdigest aggregation in scuba, we need to be able to deserialize and serialize the digests.
I added a getter for the centroids so that we can serialize the tdigest, and added a constructor to create one from the list of centroids.

Differential Revision: D8360404

fbshipit-source-id: b0f42e892f666e787e06198c7e8ff65dd8799dcc

Summary:
In folly::small_vector, we were (mistakenly) relying on a default constructor
for non-trivially constructible types.

The problem got worse on gcc 4.9, because for that compiler version, we set
folly::is_trivially_copyable to be std::is_trivial. This is mostly okay, as
std::is_trivial implies std::is_trivially_copyable. The problem is that
std::is_trivial also implies std::is_default_constructuble, which which was
breaking folly::small_vector

Reviewed By: yfeldblum

Differential Revision: D8346780

fbshipit-source-id: 9c8a9dab21ea2d4fd34f636458324915c30e10a2

Summary:
See https://gitlab.kitware.com/cmake/cmake/issues/16686

This patch was originally contributed to MacPorts by mohd-akram in https://github.com/macports/macports-ports/pull/1933.
Closes https://github.com/facebook/folly/pull/862

Reviewed By: Orvid

Differential Revision: D8346974

Pulled By: yfeldblum

fbshipit-source-id: 2673e1f414dd86bf91bb2183c2f6d9f7e72251f8

Summary:
[Folly] A shorter name for executor local variable in `Future` methods. Reads more nicely, with less awkward formatting.

When the scope of a local variable's use is just a few lines, long names are not quite so critical.

Reviewed By: marshallcline

Differential Revision: D8339451

fbshipit-source-id: 5d50cf0ce3473c1a79afeeddb9e1257cccf73e31

Summary: [Folly] No need for qualifying `InlineExecutor` in `Futures` - they are both in `namespace folly` already.

Reviewed By: marshallcline

Differential Revision: D8307058

fbshipit-source-id: 17a0ecde1e57f1c0c88cbac09bbd1bb3daf7a24e

Summary:
[Folly] Use `InlineExecutor` singleton in `Future` wait v.s. letting the executor be `nullptr`.

The effect is the same, but just more explicit.

Reviewed By: marshallcline

Differential Revision: D8306902

fbshipit-source-id: fc90704de670b1ca9956253383fadad3be297847

Summary:
Executor adaptor which allows joining only tasks scheduled through this VirtualExecutor instance without joining all other tasks in a wrapped Executor.
This is very similar to VirtualEventBase, but works for any Executor.

Reviewed By: yfeldblum, aary

Differential Revision: D8342064

fbshipit-source-id: 420b6390e2da88c4826e6d22bc8f3b3585525214

Summary: [Folly] Ensure sleep duration in logging `RateLimiter` test to make sure that there is no chance of waking up from the sleep too early.

Reviewed By: Orvid

Differential Revision: D8330018

fbshipit-source-id: f1222e1da50f8360267f9e1c5e0f24897b7b8f47

Reviewed By: shixiao

Differential Revision: D8333485

fbshipit-source-id: 02f74700272b663474c2f02535265ffb6f4bcd22

Summary:
method-level contracts

(Note: this ignores all push blocking failures!)

Reviewed By: yfeldblum

Differential Revision: D8132350

fbshipit-source-id: d79b1d88a38ea97de8d0e841e822805aff3959ae

Summary:
fbthrift needs to link against newer version of krb5 library to avoid linking
issue during OpenR build.

```
libsecurity.so: undefined reference to `error_message(long)'
```

Reviewed By: yfeldblum

Differential Revision: D8330387

fbshipit-source-id: 34f3f7361c99bb38adf558a52ef05e9d3156640d

Summary:
Make the interface consistent with the other queue algorithms.
push
try_push
try_push_for
try_push_until
pop
try_pop
try_pop_for
try_pop_until
peek
try_peek
try_peek_for
try_peek_until

Reviewed By: yfeldblum, djwatson

Differential Revision: D8262170

fbshipit-source-id: 0299e947a0069eacafd1315c920ec6e1b36675f3

Summary: Weak reference can be used if it's ok for some tasks to be dropped when Executor is destroyed.

Reviewed By: yfeldblum

Differential Revision: D8309958

fbshipit-source-id: 8ecc86a8be181a9eb695aa12305b2a30b6f4b60e

Summary:
Moved `Future::within` to `FutureBase::withinImplementation`, and changed it to return a `SemiFuture`.
`SemiFuture::within` uses it directly, and `Future::within` uses it then attaches the current executor or falls back to the inline executor to preserve existing behavior.

Reviewed By: yfeldblum

Differential Revision: D8269907

fbshipit-source-id: 76e235a2ecb2c648603961d0ac0ac17bf646d027

Summary:
[Folly] Support self-copy in `small_vector`.

And refactor move-assignment to look like the fixed copy-assignment for symmetry.

Reviewed By: Ahmed-Salama

Differential Revision: D8321122

fbshipit-source-id: 2c8b26ad6c4e538266082df29276b827cf4505fc

Summary: When vector intrinsics are not available, `visitAllocationClasses` fails to compile as it is a member function of a template class and it invokes a member function of a template base class without explicit `this->`.

Reviewed By: yfeldblum, nbronson

Differential Revision: D8300168

fbshipit-source-id: 1c1619bd1c864535648e531b218d2cf1ffef767b

Summary:
VLOG(1) shows up in Android logs, which is annoying as some of our
tools try to repeatedly connect.

Reviewed By: yfeldblum

Differential Revision: D8297987

fbshipit-source-id: 45cf4320d2e2fcf570117fee6aef133b2d9986e6

Summary:
There is no guarantee that the default branch in git is 'master'; so
    unless specified we checkout a tag along the 'dev' branch, which is not
    intended as it is the master branch that tracks releases for Zstd.

Reviewed By: jstrizich

Differential Revision: D8297843

fbshipit-source-id: 8497dc75c399ae7c86e27b28fdb73898ef4b1a4e

Summary: `s/Future/SemiFuture/` on `SemiFuture` ctor and fixed typo `s/Timeekeeper/Timekeeper/`.

Reviewed By: yfeldblum

Differential Revision: D8290658

fbshipit-source-id: 99ddbdecc0302e620bd2b4ebce74c6080cf81aec

Make Future<T>::delayed complete on correct executor 5/n: Add back Future::delayed with correct behaviour

Summary:
Overall plan to modify Future<T>::delayed to complete on the same
executor as the input future.

[folly::Futures] Make Future<T>::delayed complete on correct executor 5/n:
 * Add back future::delayed.
 * Have Future::delayed complete on input executor.
 * r-value qualify Future::delayed

Reviewed By: yfeldblum, marshallcline

Differential Revision: D8238220

fbshipit-source-id: 79afa8cc9a9fe588609ad186ad62f714ee322f7d

Summary: [Folly] Let `Sychronized` move-constructor not lock the source object, since it is an rvalue-reference and the move-constructor code may therefore be assumed to have the only live reference to the source. Same with the move-assignment operator.

Reviewed By: aary

Differential Revision: D8219883

fbshipit-source-id: f62ff87197ac4b9ceed290a73a05062ab8ed45c4

Summary:
Reusing a context can provide significant efficiency benefits.

Depends on D8172871.

Reviewed By: yfeldblum, terrelln

Differential Revision: D8287767

fbshipit-source-id: 2565e7a959b2ac0911f0a4d6e1596f9da6d12ee8

Summary:
Reusing a context can provide significant efficiency benefits.

Depends on D8172801.

Reviewed By: yfeldblum, terrelln

Differential Revision: D8172871

fbshipit-source-id: f92c85410a35643502d28922583ee0ed0b4386c9

Summary: Clear/read OpenSSL errors after certain ops.

Reviewed By: mingtaoy

Differential Revision: D8277088

fbshipit-source-id: aa436657c3bca3a081cd56858e09da57a03cda05