Summary:
Combining CancellationTokens is a common pattern in user code, which requires the user to manage a CancellationSource and attach a callback per token to be merged:
```
    folly::CancellationSource source;

    folly::CancellationCallbacki cb1{
        std::move(token1), [&] { source.requestCancellation(); }};
    folly::CancellationCallback cb2{
        std::move(token2), [&] { source.requestCancellation(); }};
    ...

    co_await co_withCancellation(source.getToken(), ...);
```

This diff adds the functionality to folly:
```
    co_await co_withCancellation(folly::CancellationToken::merge(token1, token2, ...), ...);
```

This diff subclasses CancellationState for simplicity. If the extra vtable ptr is a concern, we can instead template CancellationState to combine them, but that would come with a compilation speed penalty.

Reviewed By: yfeldblum

Differential Revision: D26277772

fbshipit-source-id: 169f65b4cf8f7f10f2800fb7797bb09379ecc239

Summary: Fix the uncaught-exception termination message expectations in `folly/lang/ExceptionTest.cpp` under libc++.

Reviewed By: markisaa

Differential Revision: D26328622

fbshipit-source-id: 2e2f9fce93c65556508d99d1f7b80f0971f35c0c

Summary: Lower min capacity so the test succeeds when ulimit -l has a lower value

Reviewed By: yfeldblum

Differential Revision: D26321362

fbshipit-source-id: 9d2c41fbbc190f46a6174c3f847943e13f5bea6c

Summary: Removed deprecated folly format APIs.

Reviewed By: yfeldblum

Differential Revision: D26317507

fbshipit-source-id: 67f42d059088946a34e77c944befa4dcb24d8673

Summary:
I've been trying to get EdenFS to compile on an M1 mac, and openssl only
support these starting with 1.1.1i. From their changelog:

    *) Add support for Apple Silicon M1 Macs with the darwin64-arm64-cc target.
     [Stuart Carnie]

Let's start by upgrading openssl.

Reviewed By: fanzeyi

Differential Revision: D26318433

fbshipit-source-id: dfe1a06ee7061dfcd026b0347eb050155895ebd9

Summary: Reexport `coroutine_handle` from `folly/experimental/coro/Coroutine.h`, which wraps inclusion of `experimental/coroutine`.

Differential Revision: D26227588

fbshipit-source-id: 32cdb2b6d87e90065bf9f140716d63670c04db5f

Summary: Similar to XLOG_EVERY_MS but for formatted messages.

Reviewed By: yfeldblum

Differential Revision: D26296133

fbshipit-source-id: 92d2e240d70cf40b903f19b0350c6d9cc0daa1fb

Differential Revision: D26265450

fbshipit-source-id: 0cefa65feb3fc3b76c1b8b8a9059dc4d321c6751

Summary: ...to avoid additional `get()` call if we need the emplaced object right after.

Reviewed By: yfeldblum

Differential Revision: D26238594

fbshipit-source-id: a66396173a27ac684b403b3c0c576be50c39dde2

Summary: `getOrCreateFn()` is prone to undefined behavior as it returns `nullptr` reference if factory function returns a `nullptr` or empty `std::shared_ptr<T>`, or if `emplace(evb, nullptr)` is called. This diff adds `DCHECK`s to enforce non-nulls. Note that `getOrCreate()` is not affected as it uses `std::make_shared` under the hood that is guaranteed to have a new object constructed.

Differential Revision: D26246552

fbshipit-source-id: b7bc7164841b70fc0889c782438bf96a61857bbd

Summary: EdenFS has a use-case for this macro but with 10+ arguments. Raise the maximum number of arguments from 7 to 15 to permit this.

Reviewed By: yfeldblum

Differential Revision: D26268587

fbshipit-source-id: be0b0579d854a93dc2983706a253370fe05905df

Summary: Add support for io_uring min capacity. This should allow us to create io_uring instances even memory is fragmented and the kernel cannot allocate contiguous physical memory for capacity CQ entries (SQ is usually much smaller).

Reviewed By: kevin-vigor

Differential Revision: D26252442

fbshipit-source-id: f4e3bd4f00d21321b77d4e1452400689dbca1073

Summary: Add `XLOG_FIRST_N` log function.

Reviewed By: simpkins

Differential Revision: D26184283

fbshipit-source-id: 23081f759897bbf7949ce603f8e5edb29869b40d

Summary: Remove FOLLY_UNLIKELY from IoUringBackend::eb_event_base_loop

Reviewed By: yfeldblum

Differential Revision: D26272113

fbshipit-source-id: de280347908e5448cc97ffc1e1be3100cf6cd4b1

Summary: Reexport `suspend_always`, `suspend_never` from `folly/experimental/coro/Coroutine.h`, which wraps inclusion of `experimental/coroutine`.

Differential Revision: D26215623

fbshipit-source-id: 5dbe5dba67e0c4dcb5a54b00753937c39833d3a7

Summary: Rely on C++17 syntactic copy elision in `DelayedInit` to simplify and write `try_emplace` in terms of `try_emplace_with`.

Reviewed By: praihan

Differential Revision: D26260351

fbshipit-source-id: 590fdfed55ee325ed8a8ae4fa68c1db0bebf1545

Summary: Move the libfmt portability code into `folly/portability/` and revise it only to mutate folly's namespace.

Reviewed By: Orvid

Differential Revision: D26182824

fbshipit-source-id: e0b72f523dfeac7ff7799ff2104a1146032dfbf3

Summary: Let folly coro headers always be buildable whether or not coroutines are available. They may just be empty apart from transitive includes.

Reviewed By: iahs

Differential Revision: D26191449

fbshipit-source-id: 5865ce5edb13f97624b9f60c45c045886fdf0bfb

Summary:
Currently, when C++ threads communicate with python's event loop, they place
the items on the queue, notify the event loop, and when even loops starts
running, they would consume all items from this queue at once.
The downside of this approach is that we are unable to deprioritize the
upstream tasks to yield to internal python tasks. However, such ability to yield
is fundamental to how Thrift approaches load shedding under overload.
In this diff we change the approach to take only a single item from the queue at a
time. Notice that if queue is not emptied, the consumer will notify the event loop to
consume from this queue on the next iteration of the loop.

Reviewed By: zhxchen17

Differential Revision: D26228933

fbshipit-source-id: 827d21df12b65d518109151cb150cd45e513da57

Summary:
Tweaks to `folly::DelayedInit`:
* No potential for ambiguity in placement-new by using `::new` and casting the address to `void*`.
* Helper functions `slot` and `store` simplify `try_emplace_with` and `try_emplace`.
* `try_emplace_with` and `try_emplace` are no longer `const`-qualified, removing the need for `mutable` qualifiers.

The emplacement members should not be `const`-qualified since they are not semantically non-modifying. The `const` qualifier signals semantic non-modification. While it is the case that there are customs around `const` qualifiers and concurrency, these customs are not the core meaning of `const`.

Reviewed By: praihan

Differential Revision: D25919779

fbshipit-source-id: 95e5c4b4abf5285fbb00dddda1192998baf6ee59

Summary:
The change aims to make it easier to catch user bugs of using the map during or after its destruction in optimized modes without ASAN.

The changes are:
- Clear the buckets_ and chunks_ pointers in the corresponding destructors.
- Add DCHECK-s of buckets_ (or chunks_) in other member functions when non-null values are expected.

Reviewed By: davidtgoldblatt

Differential Revision: D26232735

fbshipit-source-id: 14f0c11e10997773efb78c7275db99932dd19703

Summary:
When modifying code that lacks alternative variations, there is only a 'HEAD' benchmark - so it can be useful to keep a version of these results for latter printing in the format of a relative benchmark.

Add a new flag to simplify this use-case,
--bm_relative_to: A flag taking the path to a JSON-verbose formatted dump, which will be used when printing (in non-JSON-mode) to produce output relative to the provided prior dump.

Usage:
- generate a JSON benchmark dump, use "--bm_json_verbose"
  $ your_benchmark_binary --benchmark --bm_json_verbose  old-json
- run a benchmark printing a comparison to an old dump:
  $ your_benchmark_binary --benchmark --bm_relative_to old-json

Note: You can also use bm_json_verbose and bm_relative_to at the same time, this will print relative results and update the JSON dump

Reviewed By: luciang

Differential Revision: D26214397

fbshipit-source-id: 8134b74604b7bb5037934205e8eee5e3ffc27f15

Summary: If `T` is greater than 4-byte aligned, then `compact_once_flag` brings no size improvements. We can use `once_flag` in these cases, which has a better mutex (`folly::SharedMutex` rather than `folly::MicroLock`).

Reviewed By: yfeldblum

Differential Revision: D26214262

fbshipit-source-id: ea15376ea892df42cc9d3a6eac3da458fe0564a8

Summary: Original commit changeset: 149b780350bf

Reviewed By: zaxy78

Differential Revision: D26222637

fbshipit-source-id: 29bc017be6619165cbd497c27c7843fd95e345b1

Summary: This violates some expectations for how this function should be called, so explicitly allow this to be passed as a reference.

Reviewed By: yfeldblum

Differential Revision: D26215425

fbshipit-source-id: 29cff0407ec10ab61970d32da083110d1b609fbb

Summary: Non-uclibc android wasn't getting folly::remainder defined, so fall back to the STL in that case.

Reviewed By: yfeldblum

Differential Revision: D26196078

fbshipit-source-id: 149b780350bf4aaf6917ecce5e4718c91815c744

Summary: As above.

Reviewed By: luciang

Differential Revision: D26213601

fbshipit-source-id: e2eb639d0059e20cfd6828be669c62491e5ad9c4

Summary:
Add a new concept of a safe-point to folly::Task<...> with implementation-defined semantics.

Example usage:
```lang=c++
Task<> co_something() {
  while (is_work_available()) {
    co_await co_safe_point;
    do_work();
  }
}
```

Previously, a coroutine function which would cancel itself if cancellation is requested would need to spell cancellation pass-through a bit less elegantly:
```lang=c++
Task<> co_something() {
  while (is_work_available()) {
    auto token = co_await co_current_cancellation_token;
    if (token.isCancellationRequested()) {
      co_yield co_cancel;
    }
    do_work();
  }
}
```

Initial semantics include:
* If cancellation has been requested, finish the coroutine with cancellation.
* Otherwise, continue the coroutine.

In the future, it may be wise to add additional behavior:
* If the coroutine has been running for too long since its previous resumption, reschedule it.

Reviewed By: aary

Differential Revision: D25861265

fbshipit-source-id: 6da896f1529d652bfe222cf3a70e9dbe19778510

Summary: Use `LOG_FIRST_N` in `MemoryIdler` rather than reimplement it.

Reviewed By: praihan

Differential Revision: D26185702

fbshipit-source-id: c1045ef8bf6aabefa4c0806c35c156539d6e594f

Summary:
Delay registration of the timer and signal fds until running the loop first time
On some Linux kernel versions, io_uring will remove any fd registrations on thread exit. So creating the backend in a thread that exits later will cause us not to receive timer and signal fd events.

Reviewed By: kevin-vigor

Differential Revision: D26200805

fbshipit-source-id: dc3025964deb3cf87bf3e5a27141abcdb8698caf

Summary:
moving to 1.7.0 for open source github sai

also build fake with 1.7.0

Differential Revision: D26152792

fbshipit-source-id: 02e7bfb218d200666e506e3115ee8f5dba5ece0a

Differential Revision:
D26163397 (https://github.com/facebook/folly/commit/7c9f69f9c72b598c5dd942d93a94f371c6fa901d)

Original commit changeset: 48cd6cb57c48

fbshipit-source-id: fe0dd79a4e9ec77194cabf0edc697d9746542d3c

Summary:
Currently, when C++ threads communicate with python's event loop, they place
the items on the queue, notify the event loop, and when even loops starts
running, they would consume all items from this queue at once.
The downside of this approach is that we are unable to deprioritize the
upstream tasks to yield to internal python tasks. However, such ability to yield
is fundamental to how Thrift approaches load shedding under overload.
In this diff we change the approach to take only a single item from the queue at a
time. Notice that if queue is not emptied, the consumer will notify the event loop to
consume from this queue on the next iteration of the loop.

Reviewed By: andriigrynenko

Differential Revision: D26163397

fbshipit-source-id: 48cd6cb57c48ea67dce4eb5f0de6db5b0feb75ac

Summary:
Previous version does not compile when converting from `const folly::Optional`
to `std::optional`. This happens in a typical `for (const auto& x : vec)` where
`x` is or contains `folly::Optional`.

Add a new `const` version in case people case about `Value&` ctor as opposed to
`const Value&`.

Reviewed By: iahs

Differential Revision: D26137442

fbshipit-source-id: 649be596b67a01c6d1f4be341aad65f1099b74a1

Reviewed By: igorsugak

Differential Revision: D26142316

fbshipit-source-id: 6ee85228e58f5068ee14154d02ad07f731c039ec

Summary: This introduces the concept of a *concurrent* version of `folly::lazy` that stems from our own needs for use lazily instantiated class variables in a multi-threaded environment.

Reviewed By: ot, praihan, luciang

Differential Revision: D25958581

fbshipit-source-id: 6b85402708fe9ca31b4d93607cf92f23d6a3edb5

Summary: Fix broken build

Reviewed By: ispeters, Orvid

Differential Revision: D26138456

fbshipit-source-id: 8f46b268ecaf923e507db6706af7840095a151f7

Summary: DefaultCPUExecutor is the same as InlineExecutor, but hidden to avoid instantiating it to allow filtering on type, primarily in coro::task.

Reviewed By: mpark, terrelln

Differential Revision: D26077566

fbshipit-source-id: 06704134f2446727cbb9f093df0b1954b46d2e49

Summary:
The current data storage API code assumes that the MicroLock is 4-byte aligned and that the lock lives in the lowest byte of `word()`. This assumption is incorrect (see added test). We should instead rely on `baseShift()`.

This API is only used for `folly::compact_once_flag` which is new so low chance something broke.

Reviewed By: andriigrynenko, davidtgoldblatt

Differential Revision: D26091484

fbshipit-source-id: c6e6e9aa7a963cada16e0ef7783fcc6bf6d2aed6

Summary: Even though `folly::MicroLock` is 1 byte, `detail::Futex<>` (aka `std::atomic<uint32_t>`) operates on 4 bytes. So 3 bytes are accessed but not used in any way. So we need to disable memory sanitizer.

Reviewed By: andriigrynenko

Differential Revision: D26082888

fbshipit-source-id: fe585b60c96f48c02df69d182bd75a8eccde2a42