Summary:
`std::optional` allows heterogeneous comparisons, so `folly::Optional` should as well.
This allows numerical comparisons between different types, like `size_t` and `uint64_t`.

Fixes https://github.com/facebook/folly/issues/602.

Reviewed By: AsyncDBConnMarkedDownDBException

Differential Revision: D5110651

fbshipit-source-id: 34f3368283953033fbb2423ab30b04e38b5b7974

Summary:
[Folly] RFC: Embed `exception_wrapper` directly into `Try`.

Rather than storing it elsewhere on the heap. With `exception_wrapper` at 24 bytes on x64, it may now be small enough. However, it will expand the size of `Try<T>` for `sizeof(T) <= 16`, giving `Try` a new minimum size of 32 bytes on x64 instead of 16.

Reviewed By: ericniebler

Differential Revision: D5051436

fbshipit-source-id: 10d59686d64382c88d54340c97567eafb3e2f682

Summary: [Folly] Fix some old license headers.

Reviewed By: meyering

Differential Revision: D5110463

fbshipit-source-id: c7bb57194e0d33fbe1c6ddaa7d94437833b0cb0d

Add FOLLY_NODISCARD for [[nodiscard]] attribute when it exists, FOLLY_WARN_UNUSED_RESULT uses FOLLY_NODISCARD.

Summary: The `nodiscard` attribute was added to standard C++ in C++17. Prefer the standard formulation when it is available; otherwise, use `__attribute__((__warn_unused_result__))` on compilers that support the GNU extensions, and `_Check_return_` on MSVC. The old `FOLLY_WARN_UNUSED_RESULT` is now expands to `FOLLY_NODISCARD`.

Reviewed By: yfeldblum

Differential Revision: D5105137

fbshipit-source-id: 9aa22e81cd9f0b89f9343433aeae3ba365227ccb

Summary: This silences a few warnings under MSVC, and gets Folly closer to being able to compile with `-Wconversion` enabled.

Reviewed By: yfeldblum

Differential Revision: D5100686

fbshipit-source-id: e5e04c7aa143597e151a56a4d1f90dda26d0033b

Summary: Because just having a linter enforce it isn't good enough to catch everything.

Reviewed By: yfeldblum

Differential Revision: D5101828

fbshipit-source-id: a1bc482b37139a1eddeb93bc298596af950aa87d

Summary:
This makes it easier to consume Folly from a non-cmake project.
Note that this also requires making libevent, which was previously categorized as a semi-portable header into a non-portable header, meaning it can't be referenced directly. (libevent includes `Windows.h` in one of its headers -_-....)

Reviewed By: yfeldblum

Differential Revision: D5106051

fbshipit-source-id: 5ce2d4188c9036d6ab206af3036c8fd4b09516a4

Summary: To take advantage of read locks.

Reviewed By: siyengar

Differential Revision: D5106090

fbshipit-source-id: a32afd698e9204196aa3d23f21a7d41803b2eb66

Summary:
[Folly] Refactor `folly/gen/test/StringTest.cpp`.

Prefer to compare whole values once per test case, rather than sequentially comparing each part in turn.

Reviewed By: andrewjcg

Differential Revision: D5101467

fbshipit-source-id: 3d19d32bc6a5ecc5863bea76c4292935c775fe75

Summary: new method byLineFull will not trim the delimiter so that consumers can check if final line is ended up with delimiter or not.

Reviewed By: philippv, yfeldblum

Differential Revision: D5085371

fbshipit-source-id: 5045127ee11d008e3cd7d13d33bffad280fe0a7e

Summary:
Looks like we never tried to compile or run the PicoSpinLock under aarch64. There were two problems:

if sizeof(IntType) is 64, we try to do
  1 << 63
in lock and unlock. This doesn't compile because sizeof(1) is 32.

Also for try_lock, we were returning the data instead of checking for the locked bit.

Reviewed By: djwatson, yfeldblum

Differential Revision: D5091656

fbshipit-source-id: 4f81b8b32633e87b491548a1a24b9bcf20264063

Summary: A define was needed to be able to link when built against a shared-library version of gmock and gtest.

Reviewed By: yfeldblum

Differential Revision: D5100409

fbshipit-source-id: 9a4c9df20f682a25edde642c451476b2d1e1ae22

Summary: This includes adding options to toggle `/std:c++latest`, and `WIN32_LEAN_AND_MEAN`, along with giving a nice drop-down selector to `MSVC_FAVORED_ARCHITECTURE` when configured via the GUI, dropping `_WINSOCK_DEPRECATED_NO_WARNINGS` as it wasn't needed, and re-enabling warnings 4365 and 4775 within the scope of the standard library.

Reviewed By: yfeldblum

Differential Revision: D5100586

fbshipit-source-id: 87b20c6415391d4f0c75837cad5bc312910bf49f

Summary: MSVC needs these to be marked as `static` in order to be accessible within the lambdas without capturing them.

Reviewed By: yfeldblum

Differential Revision: D5099607

fbshipit-source-id: 0270e2191d504f74b1902789b662e1766b2056c4

Summary:
MSVC is being grumpy, and I want to continue to work from the preview build, so commit the workaround, as there's no significant difference.
Upstream bug report: https://developercommunity.visualstudio.com/content/problem/59614/compiler-crash-when-constexpr-constructing-stdchro.html

Reviewed By: yfeldblum

Differential Revision: D5099876

fbshipit-source-id: 64d5573d78b14339ff3177dd910a22787463ccd2

Summary: `std::hash` lives in `<functional>`, not `<xstddef>`.

Reviewed By: yfeldblum

Differential Revision: D5097468

fbshipit-source-id: d0684491d1d4b0f83f07ad837a66a915ce2ec8a6

Summary: 4.0 has been out for three months now, so it's pretty safe to remove them.

Reviewed By: Orvid, yfeldblum, mzlee

Differential Revision: D5096007

fbshipit-source-id: 595c3e86cd7cf1a1706f27f107fb0af8ab89a676

Summary: Use SafeAssert instead of assert.

Reviewed By: nbronson

Differential Revision: D5085575

fbshipit-source-id: daeff427b9b1fc5dff6ea986d16a70364acd2dd7

Summary: Name all repeating function threads for ease of debugging.

Reviewed By: yfeldblum

Differential Revision: D5065281

fbshipit-source-id: e875e654dfa644a265e44416baf5fbf23c9da434

Summary:
Previously we defined an assignment from std::string on all basic_fbstring
specialisations, but we don't actually want to do that because it's nonsense to
construct a basic_fbstring<char16_t> from an std::string. Equally it's not
nonsense to construct one of those from an std::u16string but the previous code
didn't allow it.

We now permit basic_fbstring<C, T, A1, S> to be constructed or assigned-to from
std::basic_string<C, T, A2>. The character type and traits must match but the
allocator is permitted to vary.

Background on my determination that the allocator type was unimportant and
could be disregarded: In part this is because C++17 made the same choice for
basic_string_view. Another factor was C++17's std::pmr::string (it's a
std::string with a different allocator) which I thought should be convertible
to fbstring in the same way as std::string.

Reviewed By: Gownta

Differential Revision: D5060569

fbshipit-source-id: f8984c528b76356240970c67916c58995d3f228d

Summary: It is pretty confusing to inherit from classes that manage threads. See the docblocks in this diff.

Reviewed By: yfeldblum

Differential Revision: D4973498

fbshipit-source-id: 2fcf1ddf68ef46d4d78a9b40f304262064862715

Summary:
folly/detail/ChecksumDetail.h gets included in Checksum.h and it
unconditionally includes <immintrin.h>. This doesn't compile on
aarch64 platform. Add #ifdefs for this.

Reviewed By: yfeldblum

Differential Revision: D5048636

fbshipit-source-id: d2074eb1b01487b02d95f3e2eebe683237d918fe

Summary: [Folly] Fix violations of `unused-lambda-capture`.

Reviewed By: Orvid

Differential Revision: D5060391

fbshipit-source-id: 34aabc847719603d13da8f2b52a7ec187d803a4a

Summary: It's *almost* dead. This switches things to explicitly reference `std::make_unique` so that `folly::make_unique` can be marked as deprecated until mobile catches up and it can be killed completely.

Reviewed By: yfeldblum

Differential Revision: D5026584

fbshipit-source-id: aefc8cb3de84583fd3722fdb9dfea620884590c5

Summary:
[Folly] Drop support for deprecated associative containers.

Namely, `__gnu_cxx::hash_set` and `__gnu_cxx::hash_map`.

Reviewed By: wqfish

Differential Revision: D5058813

fbshipit-source-id: ebbcf10765f5d06776ee8f697cfb78614a3a566c

Summary:
This diff adds StampedPtr, which packs a pointer and a uint16_t into
a uint64_t with maximum portability and without adding any additional
functionality.

Reviewed By: yfeldblum, davidtgoldblatt

Differential Revision: D4804614

fbshipit-source-id: 25fe7aff47d1e126ac8edfff4eb0bbb1d34071aa

Summary: AsyncSocket::handleErrMessages() should check if the error message callback is still installing before calling it, since the callback could be uninstaled on the previous loop iteration.

Reviewed By: yfeldblum

Differential Revision: D5051001

fbshipit-source-id: fc01932c0d36bd8f72bf1905f12211fb83d28674

Summary:
[Folly] List the new GCC 4.9 and C++14 minimum requirement.

We no longer support GCC 4.8 or C++11.

Closes #590.

Reviewed By: Orvid, mzlee

Differential Revision: D5058942

fbshipit-source-id: 0545d1bb294494e5ef5f17a40c9cf3ac688bd8d0

Summary:
MSVC doesn't support `^` and `&` operator for __m128i type
Closes https://github.com/facebook/folly/pull/594

Reviewed By: yfeldblum, Orvid

Differential Revision: D5053356

Pulled By: djwatson

fbshipit-source-id: f789824052e0c679c265c83ad704109805c21402

Summary:
Problems:
- The vDSO check code in configure.ac is broken, and will always fail (uses AC_LANG_PROGRAM but with arguments in the AC_LANG_SOURCE style)
- On Linux, using dlopen/dlsym requires -ldl (libdl) during the link phase. This check was missing and this argument was not added to the linker arguments.
- On a Linux system without vDSO support, libfolly.so still uses vDSO in ClockGettimeWrappers.cpp

Solution:
- Switched to AC_LANG_SOURCE
- Required libdl to exist when build target is Linux. This also adds this dependency to libfolly.la, resulting in fixing a dependency issue for Proxygen (recent Proxygen build would have issues in building examples due to failing linking step due to missing dlopen / dlsym / dlclose symbols)
- In ClockGettimeWrappers.cpp, checking if `__linux__` is set is not sufficient to determine that the system has vDSO support. The autoconf script already exposes a correct check: FOLLY_HAVE_LINUX_VDSO (this is already used in folly/detail/CacheLocality.cpp), so switched to that one.
Closes https://github.com/facebook/folly/pull/592

Reviewed By: yfeldblum

Differential Revision: D5049816

Pulled By: Orvid

fbshipit-source-id: 58b2ed4c4101274505c61b4825accf262c0d56ef

Summary:
Return not just number of cancelled ops, but all of them as well.
Test was incorrectly assuming `wait(1)` will return exactly one operation, fix
that as well.

Reviewed By: ot

Differential Revision: D5054684

fbshipit-source-id: 1c53c3f7ba855d1fcfeac8b1b27f90f0872d2c21

Summary:
[Folly] `exception_wrapper::get_object<>`.

Returns a pointer to the stored object, if the template type parameter is of the right sort.

Reviewed By: jsedgwick

Differential Revision: D5000720

fbshipit-source-id: 2869439085e8dfb56e6cb439794b03876b7d715c

Summary: This diff shows an issue in `folly::retrying`. When the future generation function throws an exception and `folly::retrying` is nested in another functor that returns Future, it will throw `broken promise` instead of the actual exception message, which can be very generic and confusing. Fix is to capture the exception so that exact error message can be propagated up.

Reviewed By: yfeldblum

Differential Revision: D5050690

fbshipit-source-id: 5b9b24977788f60aa778bb8e9cdf4281ea9a0023

Summary: To satisfy internal linter

Reviewed By: yfeldblum

Differential Revision: D4957870

fbshipit-source-id: 191ac768790fbd8cc8a4d24036c016644ff1d125

Summary: changes as suggested by FB-internal linter

Reviewed By: yfeldblum

Differential Revision: D4957742

fbshipit-source-id: c9d94c477d24f153cab0d25edccfd39ff31fdfdf

Summary: suggested by internal linter

Reviewed By: Orvid

Differential Revision: D4958232

fbshipit-source-id: 69c67d80be092db17703d672524124ca5ef7ba32

Summary: Before this change, when a non-const FunctionRef lvalue is copied, it is treated as any other callable: it is wrapped with an indirection. That's semantically incorrect and potentially creates lifetime problems. Instead, use the compiler generated copy constructor, which only copies the object and function pointers.

Reviewed By: yfeldblum

Differential Revision: D5040843

fbshipit-source-id: f691060bdced2e287ba22d22b961c02c2b924147

Summary: Instead of using `UNKNWON_UNCOMPRESSED_LENGTH` use an `Optional`.

Reviewed By: yfeldblum

Differential Revision: D5038919

fbshipit-source-id: 7fb60542277019996be3ff50509df5a5060cb1a0

Summary:
We would like to use `folly/Optional` in settings where exceptions
are disabled. An example is ObjC++ codebases where supporting exceptions
doesn't quite help (since objc_msgSend() can throw) and yet we need to pay the
additional binary size cost for the unwind tables.

This patch makes a small change to outline the "assert" utility included
inside Optional.h

Reviewed By: yfeldblum, mzlee

Differential Revision: D5030172

fbshipit-source-id: 7def3c6eda22c41c8cab2037444978e0a4c50abf

Summary:
It should be implemented with `io_cancel`, but it is not
supported (D682836), so still have to drain events, ignoring only
op callbacks.

Reviewed By: luciang, ot

Differential Revision: D5044020

fbshipit-source-id: 0bcd04c91a437fccaf2189ccf771a1cb61c68942