Summary:
When we build boost 1.69.0 with newer version of Xcode, it will fail with:

```
clang: error: unknown argument: '-fcoalesce-templates'
```

This commit fixes this build failure by telling boost's build system that we are building with clang on macOS.

Reviewed By: chadaustin

Differential Revision: D22417488

fbshipit-source-id: 0b3d22835abbba6d06812c656acb0311a60d8c67

Reviewed By: wez

Differential Revision: D22528869

fbshipit-source-id: 66c394b6fafcc45503b593f9f6b0605b5578ce56

Summary:
Fix the documentation errors in Folly when building with Xcode 12. Xcode supports validating doxygen comments by enabling the `-Wdocumentation` flag. In Clang 12, a new feature was added to warn when an inline Doxygen comment has no argument (https://reviews.llvm.org/rL367809).

`\a` and `\b` are special commands in doxygen and were being flagged as errors. I enclosed the example escape sequences within a code block to fix these errors. You can read about all the special doxygen commands here: https://www.doxygen.nl/manual/commands.html

Reviewed By: yfeldblum

Differential Revision: D22488410

fbshipit-source-id: bc4acf31b3df2a860202d0bd1ee356ce8f8fe49f

Summary:
Moveable types should have no-throw move assignment operators. `Executor::KeepAlive<>`'s move assignment operator is not marked `noexcept`. It calls the virtual `Executor::keepAliveRelease`, which is also not marked `noexcept`, despite the fact that virtually (haha) all overrides of that function do nothing more than decrement an atomic and free some resources.

This diff makes the following `noexcept`:
* `Executor::keepAliveAcquire`
* `Executor::keepAliveRelease`
* `KeepAlive::reset()`
* `KeepAlive::operator=(KeepAlive&&)`

 ---

Reviewed By: yfeldblum

Differential Revision: D22505764

fbshipit-source-id: 8e0a04e057c971673cf75da974c1abca2bdf87e8

Summary: If the caller wants a shared_ptr, UniquePtr will implicitly promote.

Reviewed By: yfeldblum

Differential Revision: D22046594

fbshipit-source-id: 2e7d527d3ca33dae974c62db909df605c532ea44

Summary:
Remove the Future-returning form of collectAny completely.

(Note: this ignores all push blocking failures!)

Reviewed By: yfeldblum

Differential Revision: D22345361

fbshipit-source-id: 180bb74c8f64052de372f5d982ad4e77cbff0119

Summary:
`std::function` has a footprint of 32 bytes and (almost) always allocates the interrupt handler. By using an intrusively reference-counted atomic pointer the footprint is just 8 bytes, and we save further 8 bytes by eliminating `interruptHandlerSet_` (it's a `bool`, but poorly aligned). This also allows to share the handler along the continuation chain, instead of copying for every core.

In addition, the `getInterruptHandler()`/`setInterruptHandlerNoLock()` API was replaced by a single `initializeInterruptHandlerFrom()`, so we don't need to expose the internal storage details anymore.

Reviewed By: yfeldblum

Differential Revision: D22474230

fbshipit-source-id: 059828de3b89c25684465baf8e94bc1b68dac0da

Reviewed By: mzlee

Differential Revision: D22495160

fbshipit-source-id: 3d6240906dd086ccac6668d907074ec7ca86ebce

Summary:
The build with Clang 10 on iOS broke with the following errors:

```
folly/detail/MemoryIdler.h:86:68: error: implicit conversion from 'uint64_t' (aka 'unsigned long long') to 'float' may lose precision [-Werror,-Wimplicit-int-float-conversion]
        static_cast<float>(std::numeric_limits<uint64_t>::max()) * h;
                                                                 ~ ^
```

```
folly/detail/MemoryIdler.h:87:38: error: implicit conversion from 'std::__1::chrono::duration<long long, std::__1::ratio<1, 1000000000> >::rep' (aka 'long long') to 'float' may lose precision [-Werror,-Wimplicit-int-float-conversion]
    auto tics = uint64_t(idleTimeout.count() * (1 + extraFrac));
                         ~~~~~~~~~~~~^~~~~~~ ~
```

This diff fixes the problem by making the existing implicit casts explicit.

Reviewed By: Orvid

Differential Revision: D22490364

fbshipit-source-id: 90bd116290de1d8906140d514f1d4880c3b3b085

Summary:
Mark the `await_resume()` method of the `final_suspend()` awaiter as `[[noreturn]]`.

This helps the compiler to dead-code eliminate this code, and in particular helps
the compiler to determine that code cannot continue execution after a
`co_yield co_error(ex)` expression (which calls `final_suspend()`).

This enables us to write code that has a `co_yield co_error()` statement as the
last line in a non-void `Task` coroutine without the compiler emitting a warning
about control running off the end of the coroutine.

Reviewed By: yfeldblum

Differential Revision: D22229020

fbshipit-source-id: b7a63b030cb42653198731d542ffa9bbf90daa83

Summary:
`boost::variant` is an expensive template, and `boost/variant.hpp` is an expensive header. In the one place it is used in futures/detail/Core.h (a commonly-included header), it can be trivially replaced with a `union`, so do so.

As a drive-by, I mark as `noexcept` those members of `KeepAliveOrDeferred` that can be done so unconditionally.

Reviewed By: yfeldblum, kirkshoop, ot

Differential Revision: D22460453

fbshipit-source-id: 5a01f873058273d1a20265507d87796450cc008b

Summary: Adds a strongly discouraged discard helper for cases where we know there is no deferred work.

Reviewed By: yfeldblum

Differential Revision: D22248947

fbshipit-source-id: 26265c33d9cd10848ab730f9c5f0356eb843025b

Summary:
Use sized-deallocation (`sdallocx`) if possible in `folly::SysAllocator` and `folly::Arena`.

`Arena` has always allocated two types of blocks:
1. Normal (fixed-sized): size is the "goodSize adjusted" `minBlockSize`
2. Large (variable-sized): when #1 is too small

Type #2 makes sized-deallocation tricky -- we need somewhere to remember the allocated sizes.

The old code used a single type `Block` and kept a single list. Here I change to have two types and two lists.  The `LargeBlock` has an additional `allocSize` data member.

This makes the Arena object itself 16B larger, but seems better than adding a 4B `allocSize` to each and every block, regardless of type.

Note that, prior to this change, it was possible to `merge()` arenas with different `minBlockSize`.  This is no longer possible.

Reviewed By: davidtgoldblatt

Differential Revision: D22466906

fbshipit-source-id: 719f357a0a1f6cfcda3208391837195c3859ab69

Summary:
Fixes include:
1. Passing "GETDEPS_BUILD_DIR" and "GETDEPS_INSTALL_DIR" env variable and using them in eden/scm/Makefile rather than assuming the source code is always in the same place regardless getdeps arguments (it isn't).
2. Added "fbthrift-source" and "fb303-source" to avoid unnecessary compilation (at least of fb303) and to put fbthrift and fb303 source code in an easy to locate place inside getdeps' "installed" folder.

Pull Request resolved: https://github.com/facebookexperimental/eden/pull/25

Test Plan: sandcastle, check oss-eden_scm-darwin-getdeps

Reviewed By: farnz

Differential Revision: D22431872

Pulled By: lukaspiatkowski

fbshipit-source-id: 8ccbb090713ec085a5dd56df509eb58ab6fb9e34

Summary:
The build with Clang 10 on iOS broke with the following error:

```
folly/test/ConvTest.cpp:321:45: error: expression does not compute the number of elements in this array; element type is 'const char *const', not 'const char *const [4]' [-Werror,-Wsizeof-array-div]
    FOR_EACH_RANGE (i, 0, sizeof(uStrings2) / sizeof(uStrings2)) {
                                 ~~~~~~~~~  ^
```

Looking at nearby uses of `FOR_EACH_RANGE`, it looks like the new compiler has caught a typo, which this diff fixes.

Reviewed By: yfeldblum

Differential Revision: D22470932

fbshipit-source-id: 3090ed9824af488fc429becf2c1084c7725daf5a

Summary:
On windows `<experimental/coroutine>` comes from the Microsoft SDK and uses the MSVC intrinsics. If you are compiling with clang this header exists but nothing from it will work because clang does not implement the MSVC intrinsics.

Further, the clang and MSVC intrinsics are ABI incompatible with each other to the extent that there is no way I can find to implement the MSVC intrinsics behavior as inline functions in a clang TU.

MS have indicated publicly that they will work with the LLVM project to make sure that clang and MSVC will be compatible for `<coroutine>`, but until then we have to say that folly does not have coroutines when clang is used on Windows.

(Note: this ignores all push blocking failures!)

Reviewed By: yfeldblum

Differential Revision: D22301662

fbshipit-source-id: 96b1c3909a3916fe300073af34429eeb5c08d1fd

Summary:
Attempt to set minimum version of an OpenSSL context through `SSL_CTX_set_min_proto_version` instead of disabling them explicitly through options, as recommended here: https://www.openssl.org/docs/man1.1.1/man3/SSL_CTX_set_min_proto_version.html

The test checks that the `SSLContext`'s `SSL_CTX` can keep a lower version regardless of the OpenSSL's configured minimum.

Reviewed By: yfeldblum

Differential Revision: D22338879

fbshipit-source-id: 356328c2ffba2a6a9d4243300a11fc823bc345d7

Summary:
D22371898 (https://github.com/facebook/folly/commit/4981497ad3333ab084e18b2a02a574cbf9438585) introduced a race by attempting to share the storage between `proxy_` and `callback_`: `setProxy()` and `setCallback()` may concurrently try to set both, and there's no good ordering we can use in `setCallback()` to fetch the proxy pointer before constructing the callback.

So revert to the logic pre-D22371898 (https://github.com/facebook/folly/commit/4981497ad3333ab084e18b2a02a574cbf9438585). This means increasing the `Core` footprint by a further 8 bytes, but D22474230 should recover that.

Differential Revision: D22474532

fbshipit-source-id: c63ca6ecd166fb71dcbeddbb2c04eb07494f99ea

Summary: Instead of hard coding the max deferred readers allowed to be 64, statically allocate large enough slots and pick max deferred readers allowed dynamically based on the platform running the service. Specifically, we set the `maxDeferredReaders = 2 * nextPowTwo(numCPU)`, which four times the number of physical cores, to allow faster reads. We are effectively giving each HW thread two slots.

Reviewed By: yfeldblum

Differential Revision: D22407478

fbshipit-source-id: 4001cf96dc502e00f00a27d57c63ba0028a52671

Summary: After D22371898 we can move the `CoreBase` implementation out of the header.

Reviewed By: luciang

Differential Revision: D22371900

fbshipit-source-id: bd4fe6df298c0ba02988b357cd7413eb8f7d8b67

Summary:
`Core<T>` instantiations share a large part of the implementation, but in the current shape the code is duplicated for each instantiation. This diff moves whatever possible to a common base class.

This diff only splits the typed and untyped parts, for ease of review. The untyped parts are moved to the cpp file in D22371900.

Reviewed By: andriigrynenko

Differential Revision: D22371898

fbshipit-source-id: db48c202d0bdcbefbebe150e7c7d9f35e06687d0

Summary:
Fix jemalloc folly weak symbol issue

(Note: this ignores all push blocking failures!)

Reviewed By: davidtgoldblatt

Differential Revision: D22420581

fbshipit-source-id: 136fa6a8c74d8fea3fc96ba1d205266f2f2fa02c

Summary:
We provide an optional callback that callers can use to save parameter names
where desired.

Differential Revision: D22399275

fbshipit-source-id: 7f9440a46cbcc4085d48a2387ca3d2db51f2fe7e

Differential Revision:
D22189916 (https://github.com/facebook/folly/commit/0d2bdbf0e0618bd9366d3c35345e091ee24f0fae)

Original commit changeset: e6fba48eaae0

fbshipit-source-id: 4ea03c56fda84240e178b2b4baf83a57d3afa344

Summary:
Use sized-deallocation (`sdallocx`) if possible in `folly::SysAllocator` and `folly::Arena`.

`Arena` has always allocated two types of blocks:
1. Normal (fixed-sized): size is the "goodSize adjusted" `minBlockSize`
2. Large (variable-sized): when #1 is too small

Type #2 makes sized-deallocation tricky -- we need somewhere to remember the allocated sizes.

The old code used a single type `Block` and kept a single list. Here I change to have two types and two lists.  The `LargeBlock` has an additional `allocSize` data member.

This makes the Arena object itself 16B larger, but seems better than adding a 4B `allocSize` to each and every block, regardless of type.

Note that, prior to this change, it was possible to `merge()` arenas with different `minBlockSize`.  This is no longer possible.

Reviewed By: yfeldblum

Differential Revision: D22189916

fbshipit-source-id: e6fba48eaae0b5cc8456b856b02d2cfc71c03834

Summary: Replace loop with clear_and_dispose()

Reviewed By: yfeldblum

Differential Revision: D22450280

fbshipit-source-id: cad040abd3f40e0fbb1f2ab27d06bf5174760c2c

Summary: IoUringBackend free mempool rework

Reviewed By: kevin-vigor

Differential Revision: D22424753

fbshipit-source-id: 5f8482702ec17561058ea841493e8a5a57b642a6

Summary: Fix issue where `preadv` and `pwritev` are now included in iOS 14 and macOS 11 SDKs, so we need to do runtime checks for those platforms.

Reviewed By: Orvid

Differential Revision: D22275221

fbshipit-source-id: 12e45c55a0fcf10f540f2d4cb9a3c392d7e182cb

Summary: `Future.h` is widely included; `KeepAliveOrDeferred` and `DeferredExecutor` are not templates, we can move all the definitions to a cpp file.

Reviewed By: yfeldblum, luciang

Differential Revision: D22371899

fbshipit-source-id: 23a77b2e0560d82f6c3006597eef85d11527cb13

Summary: processSubmit rework

Reviewed By: mokomull

Differential Revision: D22405528

fbshipit-source-id: 99db524e62264d80556e6ac771f6d504cb31bd37

Summary:
The GitHub actions have been failing because `rsocket-cpp` has been deleted.

https://github.com/facebook/watchman/runs/843777632

This commit is generated with `./opensource/fbcode_builder/getdeps/facebook/update-all-github-actions.sh`

Reviewed By: wez

Differential Revision: D22417304

fbshipit-source-id: e64a8d011c753bf8ac90ed2c9c90036baa8cf950

Summary: Implement await as a CPO - Allow customization for user defined types outside of folly.

Reviewed By: yfeldblum

Differential Revision: D22268765

fbshipit-source-id: 4badba9274b7206afc339e9d94f6ca991dc5674e

Summary:
This diff introduces a new macro function to resolve whether the current OpenSSL version available is greater than or equal to the given (major, minor, fix) version tuple.

We used the rules defined in the [OPENSSL_VERSION_NUMBER man page](https://www.openssl.org/docs/man1.1.1/man3/OPENSSL_VERSION_NUMBER.html), ie. nibbles for each of
```
 MNNFFPPS: major minor fix patch status
```

We choose to ignore `patch` and `status` for simplicity and because we don't expect to build against such versions.

The existing `FOLLY_OPENSSL_IS_110` variable already checks for greater than or equal to version number 1.1.0, so I didn't feel the need to modify it (nor the other variables). We can do some clean up in a future diff.

Reviewed By: yfeldblum, mingtaoy

Differential Revision: D22346692

fbshipit-source-id: 156ee69ecd619de12319d7d63239f28c323820a4

Summary:
move template instantiations for folly::Unit of several types into explicit instantiations in cpp files.

`folly::Future<folly::Unit>`
`folly::SemiFuture<folly::Unit>`
`folly::Promise<folly::Unit>`
`folly::SharedPromise<folly::Unit>`
`folly::futures::detail::FutureBase<folly::Unit>`
`folly::futures::detail::Core<folly::Unit>`
`folly::Try<folly::Unit>`

Reviewed By: yfeldblum, ericniebler

Differential Revision: D22092858

fbshipit-source-id: b8faa1c8aedfc193c17e2c3bc2e5b0f429ae6b0f

Summary: This commit adds a flag `--retry` to getdeps and teach it to run retry failed test. This allows us to still pass the tests when there are some flaky tests presents.

Reviewed By: wez

Differential Revision: D22291063

fbshipit-source-id: 572af48a52ceb4a9abbf530cc0154ded0120c0de

Summary:
`folly::coro::blockingWait(...)` returns `void` for `Task<void>`.

This diff implements a template specialization on taskWait for `Task<void>`

Differential Revision: D22265598

fbshipit-source-id: ff13d2b18b8706a6e8257ef706e407b315daf98a

Summary:
The variadic implementation of collectAll uses the futures APIs, and is likely to be slow.

This diff adds a fiber only version similar to fibers::foreach

Reviewed By: yfeldblum

Differential Revision: D22212232

fbshipit-source-id: f71765c5411d2c6ca4388fe373baafad65f1b01c

Summary:
After some experimenting, it is a little awkward if we want to specify a relative path based on the executable location. We'd need to add a bunch of path calculations to make it right, and I don't think the added complexity is really worth the effort.

As a result, let's just remove the use of relative path, and if we ever want to ship a copy of Python distribution, we can place it under the same directory as the binary.

Reviewed By: chadaustin

Differential Revision: D22394180

fbshipit-source-id: 86d27f6d16a03fe08826b5e5eafcef2a1c77997f

Reviewed By: yfeldblum

Differential Revision: D22393040

fbshipit-source-id: 920a7dfbf1d4334aecb475add96d3799c89aa211

Summary: Added for symmetry with `IOBuf::cloneAsValue()`

Reviewed By: luciang

Differential Revision: D21737695

fbshipit-source-id: 40f5695565ffc7d7c389c9953bffc3ab85508ed1