Summary:
Existing accessors on dynamic are cumbersome when operating on dynamics
that have optional keys or nullable values. Safely accessing these ends
up in very bloated or ugly client code, even when using getDefault().
Additionally, the move semantics of `dynamic` are usually inferred based
on the cv-ref qualification of the dynamic, and results in inconsistent
syntax depending on the situation.

`dynamic_view` attempts to resolve these issues by providing a new and
explicit API for traversing and accessing a `dynamic`. The main new
API is `descend`, which takes a varags list of keys and, functionally,
repeatedly applies `operator[]` and either returns a view of the resulting
value or an empty view if it doesn't exist or a type error occured during
descent. It only throws if another unexpected exception occurs.

`const_dynamic_view` contains copying accessors which will not throw
on a type mismatch, or if invoked on an empty view, but instead will
return a mandatory default value provided by the caller.

The other new API is only provided by the non-const `dynamic_view` class.
It is a set of value accessors which explicitly move the underlying value
out of the viewed dynamic. There is a specialization for string values
and a generic version for `dynamic`.

A helper method, `folly::make_dynamic_view` is provided which determines
the appropriate variant for a given dynamic ref.

`friend` access to `dynamic` allows optimized checks and accesses over the
regular `dynamic` APIs.

Reviewed By: yfeldblum

Differential Revision: D4917260

fbshipit-source-id: a07d26ed502aa22a5f19dd8521373a9e83fd6c02

Summary:
This is a basic implementation of adaptors for coro::Task and coro::AsyncGenerator that are compatible with https://doc.rust-lang.org/std/future/trait.Future.html and https://docs.rs/futures/0.3.13/futures/stream/trait.Stream.html.
Note that this performs blocking cancellation which may result in long destruction time/or even deadlocks if a given Task/AsyncGenerator doesn't support inline cancellation.

Reviewed By: Imxset21, c-ryan747

Differential Revision: D26938974

fbshipit-source-id: fd043304441931c6f7aa078a1a5fee50ebfa2e90

Summary: submitted by mchtech in https://github.com/facebookincubator/katran/pull/117

Reviewed By: sharmafb

Differential Revision: D27224983

fbshipit-source-id: f427f91a94ee35a48f66330e17cd56b4f9ce22c6

Summary:
[Folly] Let `assume` be invocable anytime, including before and after `main` and in signal handlers, by switching from `CHECK` to `FOLLY_SAFE_CHECK`.

Requires further minimizing the deps of `FOLLY_SAFE_CHECK`.

Reviewed By: ot, Orvid, luciang

Differential Revision: D6636035

fbshipit-source-id: 026b15ea92ba37acf9b11d714d834b79da80936a

Summary:
Depending on the environment, the type definition for `struct pthread`
(pthread implementation detail for `pthread_t`) may not be available in gdb.
If this happens, use a predefined offset for linux x86_64 to find the `specific`
field inside `struct pthread` that holds the thread-local storage values.

Reviewed By: yfeldblum

Differential Revision: D27112799

fbshipit-source-id: 38c88210c3cd2a6b06918de33167d862f59a676e

Summary:
This fixes the gdb script to handle folly_async_stack_root_tls_key being uninitialized --
this means that no async operation has run on this thread previously.

This also catches any errors raised by the `co_bt` command to help with debugging the
script itself, and to allow `thread apply all co_bt` to process all threads, even
if one thread has an error.

Reviewed By: yfeldblum

Differential Revision: D27180105

fbshipit-source-id: d6b36bdbc11b94a2f956862fc7651376e1d28af0

Reviewed By: iahs

Differential Revision: D27036059

fbshipit-source-id: 15166a6e7ec58d873a1d6799a3b1eb1ad64de420

Summary: Using a separate queue for server replies without any limit on the number of items read at once.

Differential Revision: D27090888

fbshipit-source-id: 9df44322e63a3f351a6ab4e723ead083a874b705

Summary: Rather than conditionally depending on libevent in a way which is causing downstream conflicts.

Reviewed By: Orvid

Differential Revision: D27121200

fbshipit-source-id: 4c4816e7cb2061718f81cd8a75ce4999b5b32042

Reviewed By: vitaut

Differential Revision: D27036041

fbshipit-source-id: 038b35b9690f17b59425c13c57176ac7dd017ea5

Summary:
Original commit changeset: ec402ad2badb

reverting D27044720 (https://github.com/facebook/folly/commit/bda140dc1f4be1846a19e708b7c2a0aa6215c730) to S225748

This check was added in D22272411 (https://github.com/facebook/folly/commit/0ff36eaf684ee7c1eeac0e4592e47c92f2440323) as a fix for S204433. This is very likely the cause for S225748 since the behavior is very similar to the original sev

Reviewed By: clrfb

Differential Revision: D27166845

fbshipit-source-id: c0a3f44690cd7c0df5d2a67f433419b961922dec

Summary: This is an analogous change to D6665918 (https://github.com/facebook/folly/commit/4591832b4885f166236acee689dd2b11e3b3135b), which should reduce RSS variance due to extra allocated queue segments.

Reviewed By: yfeldblum

Differential Revision: D26770721

fbshipit-source-id: 7e83aaae1d5030c5ed50b34fae06236f0ead8ac1

Summary: Patch code to address build failures discovered with GCC.

Reviewed By: ericniebler

Differential Revision: D26682213

fbshipit-source-id: a45751e00ddbce01623e266bf3d6c9a72df40d26

Summary: For reasons unknown, some gcc versions disliked the previous code with the constexpr pointer variable, even though most supported compilers and versions accepted it.

Reviewed By: aary, luciang

Differential Revision: D27083528

fbshipit-source-id: b225a3f211a9b51b248cc079cf11e4e25ae30460

Summary:
As title.  CLI applications that don't use gflags might not care about
process-wide gflags, so add an option to kill it.

Reviewed By: yfeldblum

Differential Revision: D27066900

fbshipit-source-id: d412391879cd5ac89eba5903fd033775cf0ca49a

Summary: By returning a generic KeepAlive<> the global IO executor was losing the IOExecutor interface. This fixes it by returning the right type.

Reviewed By: yfeldblum

Differential Revision: D27061083

fbshipit-source-id: d57f67982c3467a6b814b17e851e4513ffd33502

Summary: Add `reset_once`, a mechanism to reset a `once_flag`.

Reviewed By: Mizuchi

Differential Revision: D27071246

fbshipit-source-id: 4824782fb0ce6380b72e3e657e6f5073029eaf14

Summary: A helper for use with check functions using `FOLLY_KEEP`.

Reviewed By: luciang

Differential Revision: D27072070

fbshipit-source-id: 9c106ca1e0854b0f16453e8ad73d7001c3b7fff6

Reviewed By: luciang

Differential Revision: D27071414

fbshipit-source-id: 8bbe12e8f8264f2040c030e0353e1e4d59efae55

Summary:
When folly::AsyncSSLSocket is used in unencrypted mode, zero copy is
possible due to OpenSSL being bypassed, but the setZeroCopy() override in
AsyncSSLSocket prevents zero copy from being used. Remove the override (no
callers currently check the return value anyway).

Reviewed By: yfeldblum, yqz, jalatif

Differential Revision: D27044720

fbshipit-source-id: ec402ad2badb84150ecd1b7639770a49e16e9183

Summary: Add `CoInvokeWithoutArgs` helper, coroutine-aware version of `InvokeWithoutArgs`

Reviewed By: yfeldblum

Differential Revision: D27060013

fbshipit-source-id: 8024a5818fbe7759d3f9827d260c4e7370444bb0

Summary: Encourage new uses to use the overload which does not take an explicit list of exception types.

Reviewed By: aary

Differential Revision: D27041702

fbshipit-source-id: aa808bb432c2aea6e2c1cb10d76f2492875bae93

Summary: Fix -Werror,-Wshadow-uncaptured-local errors

Reviewed By: yfeldblum, iahs

Differential Revision: D27052090

fbshipit-source-id: 843bf9374ff16bfe422ef78e889f1c1286335c1a

Summary:
Principally, this change shrink the code generated by `FOLLY_SAFE_CHECK` by:
* Moving the literal arguments which would be passed to the backing functions into a constexpr data structure and passing only a pointer to that data structure.
* Passing all the arguments through via C variadic arguments rather than inlining the sequence of calls to handle them into the caller.

Reviewed By: swolchok, luciang

Differential Revision: D26996101

fbshipit-source-id: 61c39c08758a9de28ba0cfd342b174185e80ad9f

Summary: In particular, let `make` and `ctor` take variadic arguments since there is no cost.

Reviewed By: iahs

Differential Revision: D27024839

fbshipit-source-id: 805c65fdc79f60af1256a4c36be94bb22c163bdd

Summary: So that downstream locations do not have to write their own noop functions.

Reviewed By: iahs

Differential Revision: D27022664

fbshipit-source-id: e8f69c7babf853a71dedd24ded59c5017cf18ad6

Summary:
The interface:

  erased_unique_ptr
  to_erased_unique_ptr
  make_erased_unique
  copy_to_erased_unique_ptr
  empty_erased_unique_ptr

Reviewed By: iahs

Differential Revision: D26980776

fbshipit-source-id: c520993a2191e7f74c5056a4854e2b85731a09a0

Summary: `snprintf` may not be async-signal-safe, but Elf code is intended for use in signal handlers.

Reviewed By: luciang

Differential Revision: D27000080

fbshipit-source-id: 818f48787b5712b7334eca782e18c71c17d03361

Summary: This adds the ability to print the async stack trace from where the exception is thrown.

Reviewed By: yfeldblum

Differential Revision: D26989150

fbshipit-source-id: 2edfadfa617d407df947987d962617129d626040

Summary: Add some functions that can be used to inspect the generated code for `FOLLY_SAFE_CHECK` and `FOLLY_SAFE_PCHECK`.

Reviewed By: swolchok

Differential Revision: D26996102

fbshipit-source-id: 257f59d5904c319ed01e55cfd75939b41e55c53d

Summary: Task forces a copy of the passed-in token even when it's an rvalue, which results in two unnecessary atomic operations on the shared state. Take by value to allow moving. AsyncGenerator already does this.

Reviewed By: yfeldblum

Differential Revision: D26991772

fbshipit-source-id: 4697e36626158155329306928cbd1e7e69b8bd01

Summary:
This makes it possible to pass `FixedString` objects to APIs that accept
`std::string_view`.  `FixedString` already had implicit conversion to
`std::string` and `folly::StringPiece`, this simply implements parity for
`string_view`.

Reviewed By: yfeldblum

Differential Revision: D26940391

fbshipit-source-id: 5f411ef9a901e0855593b090f1cbe3345971a140

Summary:
`folly::Symbolizer` uses `FOLLY_SAFE_CHECK` -- which is signal-safe, but it only says "this thing broke".

I plan to changes these to add more details about what exactly broke:
from:
   FOLLY_SAFE_CHECK(die.abbr.tag == DW_TAG_compile_unit, "expecting compile unit entry");
to
   FOLLY_SAFE_CHECK(die.abbr.tag == DW_TAG_compile_unit, "expecting compile unit entry, found: ", die.abbr.tag);

Reviewed By: yfeldblum

Differential Revision: D25992552

fbshipit-source-id: ae678b45606afc519704767844a973d499c60c73

Differential Revision:
D26612326 (https://github.com/facebook/folly/commit/28799ed1d609bb1aca82464be8ad9dbf4e9f1b39)

Original commit changeset: d56c892c87ba

fbshipit-source-id: 77f8a7c58bfced197558ed29912ace457a089baa

Summary:
We have found that BitVectorCoding.h incorrectly outputs
-Wdivision-by-zero errors when another file that includes it fails to compile.
In the absence of other compilation errors, the -Wdivision-by-zero error does
not appear (since the compiler correctly can tell that "division by zero" is
not an issue in the code).

In order to get rid of these erroneous error logs, we decided to replace the
if-statements that surround the divisions (and check that the divisor is not
zero) with `if constexpr` statements since those will stop the compiler from
mistakenly thinking that division by zero is possible.

Reviewed By: ot, philippv, luciang

Differential Revision: D26961916

fbshipit-source-id: f65ef6d7782c94e58d6d28b9f8b053f205e3b7c1

Summary: Using a separate queue for server replies without any limit on the number of items read at once.

Differential Revision: D26612326

fbshipit-source-id: d56c892c87bafa701c12b6da780e9b2d4710ee2c

Summary: `to<T>` already works in simple cases when `IsSomeString<T>`; by generalizing `parseTo` any string-like `T` gets full functionality without having to copy-paste the overload.

Reviewed By: yfeldblum

Differential Revision: D26831450

fbshipit-source-id: c09629bb7173dde1e0986654128b8e1d7c48b9ba

Summary:
`net_tstamp.h` is incomplete on some platforms, particularly OSS.

One option would be to make `FOLLY_HAVE_SO_TIMESTAMPING` conditional on all of the timestamp flags being present. However, I'm instead going to just decouple this support from the underlying platform's headers.

Reviewed By: rsunkad

Differential Revision: D26971541

fbshipit-source-id: 01b24f57ab827aca42889138e4cca4d488ae0940

Summary: Remove the default argument for the deprecated createUnique operation for SerialExecutor.

Reviewed By: yfeldblum

Differential Revision: D26916321

fbshipit-source-id: e6fb1766bfaae4d6e702982c5527d483e6d8c036

Summary:
Under gcc and clang, we use the intrinsic `__builtin_clzll`. This builtin is available regardless of whether the `clz` instruction is available on the target platform - when it is, the backend chooses it; when it is not, the backend emits emulation code.

Under msvc, the builtin is `__lzcnt64`. However, this builtin is available only in x64 builds; there is no fallback to emulation code, and 32-bit builds fail to compile.

Differential Revision: D26918251

fbshipit-source-id: a4d9c199f632c5a210bd6fd8782d327f7aac774e