Summary: Consume `folly::dynamic` and if it matches JSON patch format, build a sequence of patch operations. Application is to be done separately, e.g. by a method of `folly::dynamic` by walking the operations vector (obtained after parsing the patch) and applying operations to the document. This mimics the approach we used previously with `folly::json_pointer`.

Reviewed By: yfeldblum

Differential Revision: D10017234

fbshipit-source-id: 1d0b9f0967e528b81abf7998c88abdaf70a2fce8

Summary: There are no other methods, and icc gets confused otherwise

Reviewed By: yfeldblum

Differential Revision: D10116562

fbshipit-source-id: 7664501b910e5857e32337d3583dcc948caddd5d

Summary: icc doesn't support it.

Reviewed By: yfeldblum

Differential Revision: D10116547

fbshipit-source-id: 1ed522bd373ab30507f713d855ef02027ce90a91

Summary:
Having Indestructible field in SettingsCore makes it leak memory when
threads die.

Reviewed By: yfeldblum

Differential Revision: D10118572

fbshipit-source-id: 68696983128049525018a911b03cb7ea8add53ab

Summary: [Folly] Declare deleted `new` and `delete` operators in pairs in `ScopeGuard`.

Reviewed By: Orvid

Differential Revision: D10119848

fbshipit-source-id: 3588ed299248efd124d216bfaf5e472795f6a7aa

Summary: [Folly] Closer guarantee of `constexpr` Fingerprint tables computation. Works around a limitation that `template <...> constexpr` functions are only sometimes `constexpr` and may be non-`constexpr` for some instantiations with no warning by enforcing `constexpr` for the instantiations used.

Differential Revision: D10116556

fbshipit-source-id: f7014e5b2fce411c27c331874a7fd33841e14df3

Summary: This fixes a linker issue

Reviewed By: tuomaspelkonen

Differential Revision: D10109866

fbshipit-source-id: bf4193eafc8eb6f75b84241ff6e2ef89ef866642

Summary: SSL_CTX_new can fail if OpenSSL is not initialized.  This ensures it is.

Reviewed By: bolekk

Differential Revision: D10105302

fbshipit-source-id: 4da40d4714747b0e6a359a52fa594fc29bb93c0a

Summary:
Current thread was previously blocked waiting on the Future to be completed anyway, so there's no reason to not treat it like one of the ObserverManager threads (if it isn't one already) and run the computation inline.
Without this change nested makeObserver calls could result in a deadlock if recursion depth was greater than the number of ObserverManager threads.

Reviewed By: yfeldblum

Differential Revision: D10097363

fbshipit-source-id: eb781ed5aea0ad9415da40fbc7f1c15ed481e92f

Summary:
This allows a caller to throw away unwanted parts e.g.

```
std::string user;
folly::split('/', "ads_lla/admarket/adfox", std::ignore, user, std::ignore);

```

Reviewed By: yfeldblum

Differential Revision: D10057247

fbshipit-source-id: 8198d4cb207bbd2007635db1e5796759dccf367c

Summary:
SettingsMetadata provides a type-erased view, so the default value is stored as a string representation.
This method allows getting the actual original default value.

Differential Revision: D10077879

fbshipit-source-id: 2c6bf15eba57da5cb33ad1c657bc9bd51bcd2946

Summary: This forces users to take a Snapshot and makes global settings updates both atomic and more explicit.

Differential Revision: D10055254

fbshipit-source-id: 73ce34acdadad19d5b75e74ad26f13dc7763228d

Summary:
See the unit test for example usage.

```
folly::settings::Snapshot snapshot;

// Now changes to `FOLLY_SETTING(project, name)` and `snapshot(FOLLY_SETTING(project, name))`
// are independent from each other.
// Any updates to the settings in the snapshot can be published via snapshot.publish()
```

Basic version with a global lock, there are ways to optimize this later.

Differential Revision: D9926070

fbshipit-source-id: 66ee7f28539c242a08b688eab4a18e4a42a8b0ff

Summary: [Folly] Various `noexcept` specifiers in `IOBuf`.

Reviewed By: Orvid

Differential Revision: D10081705

fbshipit-source-id: 5516e7deca4edd50ea99e61e10cd413f3c0f17ae

Summary: [Folly] Compute fingerprint tables at constexpr time, v.s. as a separate build step which generates a source file.

Reviewed By: Orvid

Differential Revision: D10081043

fbshipit-source-id: f01f7587aafd29fc1c44515730b759325e1566d8

Summary: Currently for `ElfFile::openNoThrow`, if `init` fails (due to mal-formatted content etc.) it won't unmap and close the file. They will only be unmapped / closed on destruction. This Diff calls `reset()` on that case.

Reviewed By: yfeldblum

Differential Revision: D9997690

fbshipit-source-id: c30907fb793c813a5ad40d249919dd1752a2d711

Summary:
The signal handler might use nearly 9KB stack for symbolization. That would
cause stack overflow if the signal handler is running on a small alternative
stack set by sigaltstack. We have seen that in Rust programs. The Rust stdlib
sets up [8KB](https://github.com/rust-lang/libc/blob/4bd52f5e3ef5d6c8abdd1fbaf7c9975800a0dc93/src/unix/notbsd/linux/other/b64/x86_64.rs#L505) stacks [using sigaltstack](https://github.com/rust-lang/rust/blob/55b54a999bcdb0b1c1f42b6e1ae670beb0717086/src/libstd/sys/unix/stack_overflow.rs#L173) for all threads created by Rust on x64 Linux.

Talked with jsgf, we'd still like to get a nice symbolized stack trace if
segfault happens in a binary including both Rust and C++ code, since it's
more likely the C++ part being wrong, so C++ symbol demangling is more
important than Rust demangling.

This diff detects the small sigaltstack case, then allocates larger stack for
symbolization. Note the stack manipulation logic is not signal-safe, so it's
not used for non-small-sigaltstack cases. Programs not using sigaltstack, or
use sigaltstack with >9KB stacks won't be affected.

As we're here, teach the signal handler to save and restore errno. Also add
a note about golang's SA_ONSTACK requirement.

Reviewed By: luciang

Differential Revision: D9846902

fbshipit-source-id: f0dc81b1c1249d8a724e112906e0ff0b14c14ea9

Summary: This demonstrates a deadlock that's possible when using InlineTask.

Reviewed By: lbrandy

Differential Revision: D9883432

fbshipit-source-id: 45bb14181f6cfec41851315c0369232a30ba13d9

Summary:
It seems like memdup may fail in certain builds with nullptr, 0 and cause OpenSSL to put a malloc failure on the stack.  See https://github.com/openssl/openssl/blob/master/ssl/ssl_lib.c#L2752

This diff clears the error stack when we do this.

Reviewed By: knekritz

Differential Revision: D10037676

fbshipit-source-id: ea7b136cafde818564e8ee2401f0cef30f52a45d

Summary: Because DeferredExecutor now acts as a simple proxy to user executor, we can actually support multi-hop SemiFutures.

Reviewed By: LeeHowes

Differential Revision: D9928793

fbshipit-source-id: c7e030bac3582b2931bc9639c766a4398ce23a76

Summary:
This diff adds support for doing heterogenous lookups
to the dynamic::get_ptr(dynamic) function.

Reviewed By: yfeldblum

Differential Revision: D10007208

fbshipit-source-id: 2453f3fe8ab36dfd9e5627aa75cf8eb7aee51699

Summary: Move the wait() and timed_wait() functionality out of DeferredExecutor. This is now possible because folly::Futures are using Executor::KeepAlive to manage executors' life-time.

Reviewed By: LeeHowes

Differential Revision: D9925417

fbshipit-source-id: e9818417048f44ee66648439e781060fdabca6b9

Summary:
MSVC (14.12.25827, VS 2017 15.5) fails to compile with internal error when using `/std:c++14` parameter:
```
Future-inl.h(1484): fatal error C1001: An internal error has occurred in the compiler.
(compiler file 'msc1.cpp', line 1507)
 To work around this problem, try simplifying or changing the program near the locations listed above.
```

Reviewed By: yfeldblum, Orvid

Differential Revision: D10018915

fbshipit-source-id: ba886265b68684aacc2bf471c79ba6c39e611c8e

Summary:
If `Source` isn't copyable, parallel generator cannot be composed
further due to implicitly deleted move ctor.

Example:

```
byLines(File(...))
| parallel(map(...))
| sum;
```

Reviewed By: ddrcoder, ot

Differential Revision: D10004477

fbshipit-source-id: 51ce23e834413bd53547a683f8ed89a1811f74a2

Summary:
Some of the error messages had the incorrect expected types.
Fix those occurences

Reviewed By: shixiao

Differential Revision: D10003775

fbshipit-source-id: ba8e3b7d14ee2c5442dfd24b9fbf7775d601f6f0

Summary:
Deprecate the legacy forms of Future::then to assist migration to thenValue and thenTry.

This is part of a longer process to improve type correctness for folly::Future. By separating the forms of then we no longer have ambiguity when passing a polymorphic lambda as a continuation and can more easily tweak the implementation to modernise it.

Reviewed By: yfeldblum, WillerZ

Differential Revision: D9974379

fbshipit-source-id: 26f986329cb5d2d33d366b8f9e7b2664656642ff

Summary:
Add implementation for std::hash<MacAddress> so that it can be used in
maps.

Reviewed By: yfeldblum

Differential Revision: D10004544

fbshipit-source-id: 46cb177577123b1248cd8ff679f0fbe286596819

Summary: To allow deprecation, remove use cases of Future::then inside FutureSplitter.h

Reviewed By: yfeldblum

Differential Revision: D9995264

fbshipit-source-id: d44c63c45a08ca675b9bff33fabcbb2836ea2a64

Summary: Went a step too far removing then from inside Future-inl.h. Map needs to be generic over value/try. Just remove that change for now.

Reviewed By: yfeldblum

Differential Revision: D10002565

fbshipit-source-id: c37f744d47f9dd123114b6b62c1c832519cb4f8e

Summary: [Folly] A faster `empty()` shortcut in `IOBufCompare`.

Reviewed By: spalamarchuk

Differential Revision: D9981606

fbshipit-source-id: 4a9762b83fe2f26b1387c162a1e23c201088977f

Summary: [Folly] Let `IOBufCompare` have a self-compare shortcut.

Reviewed By: vitaut

Differential Revision: D9981523

fbshipit-source-id: e984cffc2816a0f4f06bf418b16d4d3eb055f6ef

Summary: To allow deprecation, remove use cases of Future::then inside Future.h/Future-inl.h.

Reviewed By: yfeldblum

Differential Revision: D9984465

fbshipit-source-id: 48e8a5b2985c86fd5384e43e6df282da298b1d99

Reviewed By: zertosh

Differential Revision: D9993527

fbshipit-source-id: 52c4c0bfe6b5c73c652dd350f599fb846a003a4f

Summary: (Note: this ignores all push blocking failures!)

Reviewed By: spalamarchuk

Differential Revision: D9994424

fbshipit-source-id: 2055d3b09ce2e1d783624a9902463efade4714d4

Summary:
This is known at compile time, but we still pay the cost since
SettingCore has to look it up through its own reference.
Hint it directly at the callsite instead.

Differential Revision: D9983460

fbshipit-source-id: 1c6ca5e3cbd9e859ba88d641cdca59f0d4d65dfb

Summary: Requires a new header to break the circular dependency

Differential Revision: D9983196

fbshipit-source-id: f15ab3c6128d30906ac25384df92813aa9d76c9a

Summary:
- Change the get() API to return T by value if T is small
- Internally store small T in a global atomic to avoid thread local lookups

Differential Revision: D9982433

fbshipit-source-id: c42d06a75b9ff48307a90f77d0bb72bfa6375d6c

Summary: Makes further changes cleaner

Differential Revision: D9982335

fbshipit-source-id: 19268c8e3fc1b6aee589a8d3d38b0348db8c5a43

Summary: inline the small, fast path only

Differential Revision: D9982097

fbshipit-source-id: f1bcbab2b444d372e178aa548175a5c27be972b6

Summary:
With this change the setting lookup is now inlined at each callsite as:
```
if (UNLIKELY(global_setting_ptr == 0)) {
  global_setting_ptr = &initialize_setting(); // OK to race
}
// use *global_setting_ptr
```

Differential Revision: D9981958

fbshipit-source-id: a04b296d8345d1bb37dc06ce72277e00e745a94a