Summary:
Document that `future.then()` is identical to `future.unit()`.

Put functions next to each other to make it clear, and use identical
wording.

Reviewed By: yfeldblum

Differential Revision: D5955451

fbshipit-source-id: 1b55d5785dc0995d4d9364f48241e98ad01b31f4

Summary:
[Folly] Remove `Executor::addPtr`.

It was there to support passing non-copyable callable objects wrapped as `std::shared_ptr`. It is no longer useful since we have `Function`, which is a non-copyable version of `std::function` which can support capturing non-copyable objects, and it is generally unused.

Reviewed By: spacedentist

Differential Revision: D5983801

fbshipit-source-id: b49a86f8dd7e5250a097b0e714a1bdf9ac362916

Summary: I recently got a gcc crash when using `ConcurrentHashMap`

Reviewed By: djwatson

Differential Revision: D5994587

fbshipit-source-id: 412d48aa6da12c428bb9ab5ed7a317d89c9580b9

Summary:
Add `SocketAddress::makeFromPath(StringPiece)` static member function to
constructor `SocketAddress` from a path to Unix domain socket.

Reviewed By: yfeldblum

Differential Revision: D5974523

fbshipit-source-id: b5c1537e67d07d1ef401fea75e35753392eeaf6b

Summary:
[Folly] Use fewer keep-alives in `VirtualEventBase::keepAliveRelease`.

{D5982132} mistakenly used `VirtualEventBase::add`, which holds a keep-alive on the master `EventBase`, instead of calling `EventBase::add` directly.

(Note: this ignores all push blocking failures!)

Reviewed By: andriigrynenko

Differential Revision: D5992403

fbshipit-source-id: f427025c06f01e6a93d6eae8a051c3553f58be20

Summary: [Folly] Make `keepAliveRelease` consistent between `EventBase` and `VirtualEventBase`.

Reviewed By: elsteveogrande

Differential Revision: D5982132

fbshipit-source-id: 536d48e5672567e78786691bfb283c34d1f31960

Summary:
[Folly] Move `GlobalThreadPoolList.h` into `folly/concurrency/`.

This seems like a better place than the top-level. It seems reasonable because this has *something* to do with concurrency. This is used by executors, but is not itself an executor, so it was not clear that it should go to `folly/executors/`, although that also seems like quite the reasonable choice.

Reviewed By: Orvid

Differential Revision: D5985142

fbshipit-source-id: 6117d133757af74023d6cffb838741da83d173bd

Summary: Allows calling backlashify on a StringPiece.

Reviewed By: yfeldblum

Differential Revision: D5930015

fbshipit-source-id: ca14c78d9a90c45781da7229eb5d2f437792b2d1

Summary:
Offer a clean separation between future as a vocabulary type for crossing
library interfaces, and future as a type to manage continuations.

The principle is that if we want an API with clean separation of execution it
should both return and receive SemiFutures. The returned SemiFuture would
only be awaitable, but not continuable. If the caller wants to enqueue a
continuation then it is efficiently convertable into a folly::Future by
calling .via.

This means that an API a) Does not have to take an executor to ensure it
returns a valid future. That can be deferred to the caller or the caller's
caller/target for true separation. b) The API can ensure that its own executor
is not exposed to the caller, while still having a clean API.

Obviously if some API wants to allow returning of a continuable future, then it
can also provide an executor-taking API.

Reviewed By: yfeldblum

Differential Revision: D5769284

fbshipit-source-id: 46241d1274bf7b1698a7d28a47cff2a65a983740

Summary: Exception types should have default visibility, otherwise RTTI doesn't work right.

Reviewed By: elsteveogrande

Differential Revision: D5976415

fbshipit-source-id: 45dcfe3476b513aa49a6f78352318f31d381ada7

Summary:
[Folly] Move keepalive-acquire code into `Executor::keepAliveAcquire` overrides.

This makes the API more symmetric and allows for more flexibility. Also serves as preparation for generalizing the keepalive-token interface.

Reviewed By: andriigrynenko

Differential Revision: D5974080

fbshipit-source-id: 26209e49a0f5834ba229d4bbfc9272c2e4ffb3fd

Summary:
I couldn't find anything that consumes `--json` output, so I made this. It prints out benchmark results from two runs, comparing each benchmark to its corresponding baseline. This should help with benchmarking changes across revisions.

Along the way:
- Two small transparent `struct`s replaces the use of `tuple`s everywhere.
- New output JSON format (additive), formatted as array of arrays so order is preserved.
- New comparison binary in `folly/tools/benchmark_compare`

Sample output:

{P58307694}

Reviewed By: yfeldblum

Differential Revision: D5908017

fbshipit-source-id: d7411e22b459db16bd897f656e48ea4e896cb1bf

Summary:
[Folly] Let keep-alive tokens from `VirtualEventBase` be destroyed from any thread.

This case was missed in {D5951397} (facebook/folly@6f3b7616f3402355441c62ca60a36159435aa818).

Reviewed By: andriigrynenko

Differential Revision: D5970670

fbshipit-source-id: 19e2b00134516e68113234acd6111e21c3e23e8d

Summary: The previous change can lead to deadlock. Backing out.

Reviewed By: djwatson

Differential Revision: D5957084

fbshipit-source-id: 72ea1cb6236367912b4b087da7e4d57f8a2daed0

Summary:
Three fixes:
(1) The compiler reports UB in line 432 for the case M > HAZPTR_TC_SIZE even though it is executed only if M <= HAZPTR_TC_SIZE. Added a condition M <= HAZPTR_TC_SIZE to help the compiler determine that line 432 is not executed in that case.
(2) Added missing management of empty state in hazptr_array move operator
(3) Added nullptr argument to empty hazptr_array in Array test

Reviewed By: djwatson

Differential Revision: D5951283

fbshipit-source-id: cb8e61421ab06c7733f67bf2d2274d3311260ac4

Summary: [Folly] Let keep-alive tokens be destroyed from any thread.

Reviewed By: andriigrynenko

Differential Revision: D5951397

fbshipit-source-id: 91e72588de4ef33a730ebef5770e77635d4e93ba

Summary:
```lang=cpp
folly/test/stl_tests/StlVectorTest.cpp:1975:11: error: parentheses were disambiguated as redundant parentheses around declaration of variable named 'm' [-Werror,-Wvexing-parse]
    Vector(m);
          ^~~
folly/test/stl_tests/StlVectorTest.cpp:1975:11: note: add a variable name to declare a 'Vector' initialized with 'm'
    Vector(m);
          ^
           varname
folly/test/stl_tests/StlVectorTest.cpp:1975:5: note: add enclosing parentheses to perform a function-style cast
    Vector(m);
    ^
    (        )
folly/test/stl_tests/StlVectorTest.cpp:1975:11: note: remove parentheses to silence this warning
    Vector(m);
          ^ ~

1 error generated.
```

Reviewed By: Gownta

Differential Revision: D5955613

fbshipit-source-id: 3015570ce111603b3561914d07b55365a221c686

Summary: [Folly] Move `Merge.h` into `folly/algorithm/`.

Reviewed By: Orvid

Differential Revision: D5951346

fbshipit-source-id: 487203e55e2a44888e599ca22849798154e5b386

Summary:
Changes:
- Added hazptr_local<M> for optimized management of local hazptr_holder-s.
- Added hazptr_array<M> for optimized management of hazptr_holder-s
- Added benchmarks for hazptr_local and hazptr_array
- Added tests for hazptr_local and hazptr_array
- Changed SWMRList example to use hazptr_local<2> instead of two hazptr_holder-s.
- Updated benchmark performance results.

Reviewed By: davidtgoldblatt

Differential Revision: D5833721

fbshipit-source-id: 154811f67c38abac7342cecb71f829778ccf76b2

Summary:
As title. No sense adding a timeout to the timeout manager when the future is
already complete.

Reviewed By: yfeldblum

Differential Revision: D5933144

fbshipit-source-id: 4d1bbd866c47ccee6bd0518cbe063afc1d34cbca

Summary: This is deprecated and not used.

Reviewed By: yfeldblum

Differential Revision: D5936286

fbshipit-source-id: 68f757be06ebe375e14db008d0e5828fad0c3aa5

Summary: To be used to signal that data that was sent as TLS 1.3 early data was lost. This needs its own exception type as it requires special handling (ie it should usually be retried immediately).

Reviewed By: siyengar

Differential Revision: D5869914

fbshipit-source-id: ca0d8ef19cb991e9d6ffe0f8c99abfb03b748ce6

Summary:
On MacOS compiling unittests with "make chek" shows the following compile
error:
```
../futures/test/RetryingTest.cpp:168:26: error: no matching function for call to 'min'
 newMemLimit.rlim_cur = std::min(1UL << 30, oldMemLimit.rlim_max);
```
Closes https://github.com/facebook/folly/pull/680

Reviewed By: elsteveogrande

Differential Revision: D5921433

Pulled By: yfeldblum

fbshipit-source-id: 236d8336f852750a983c2e268db8811d1a4ed9ee

Summary: Objective-C blocks are stack allocated, and unless there is a proper assignment it isn't retained and the memory is freed. Because folly::Function used to move, it would hold a reference, but after switch to a constructor by-value, it no longer does this and we see a use-after-free.

Reviewed By: yfeldblum, ericniebler

Differential Revision: D5888606

fbshipit-source-id: fe4cabb2f2ae289cce0e7429e0af3935ba314720

Summary:
[Folly] Let `ProcessReturnCode` be publicly constructible.

Via provided constructor functions, which limit how it may be constructed so that it is only constructible into a valid state.

Differential Revision: D5898739

fbshipit-source-id: 7490018adfc39408b4290248ef1220e8fd0238cb

Summary:
[Folly] Avoid tautological compare in `folly/experimental/symbolizer/`.

`x < 0` when `x` is unsigned is tautological and there are warnings against such comparisons. The underlying type of an unscoped enumerations without a fixed underlying type is not specified, and whether it is signed is also not specified; it could be unsigned, and is unsigned in practice in common cases.

Reviewed By: Orvid, eduardo-elizondo

Differential Revision: D5897792

fbshipit-source-id: 24d84f9bf2c61c907585e1b675c2bbf11ef1720b

Summary:
If a lock is stolen from fiber f1, and then fiber f2 is notified before f1 one
wakes up and discovers the crime, then f1 will clear notifiedFiber_ so that f2
thinks the lock was stolen from it as well and hence recurses back into lock().

Reviewed By: andriigrynenko

Differential Revision: D5896323

fbshipit-source-id: 528ec1ed983175d3e08f3dc07b69bbc783a86cfb

Summary:
folly/test/stl_tests/StlVectorTest.cpp was too slow under
mode/dev-asan, resulting in timeouts, and the relinquish test allocated
with malloc and freed with operator delete.  This diff reduces the vector
size for testing under ASAN, and fixes the allocation mismatch.

Reviewed By: Orvid

Differential Revision: D5890969

fbshipit-source-id: 49a9498f6c0c4b3c7165906efd1262e518fea810

Summary: This is more convenient to use (for example with an IOBufEqual matcher).

Reviewed By: yfeldblum

Differential Revision: D5882029

fbshipit-source-id: 6aa12f80479f40bcc2af64dc270fb0a9382983b5

Summary:
This adds a gdb deadlock detector script into a new directory in folly. I
chose to put it under the `experimental` directory and not the top-level
directory as we have only tested these scripts on x86_64 Linux and not other
types of platforms.

This diff includes:
- a README on the contents of this directory and how to use the scripts
- a script to detect deadlocks

gdb directory
---------------

This new directory will contain a collection of gdb scripts that we have
found helpful. These scripts use the [gdb extension Python API](https://sourceware.org/gdb/current/onlinedocs/gdb/Python.html#Python).

To run the scripts, fire up gdb and load a script with `source -v`. Example:

```
$ gdb -p 123456
(gdb) source -v ./folly/experimental/gdb/deadlock.py
Type "deadlock" to detect deadlocks.
(gdb) deadlock
Found deadlock!
...
```

deadlock detector script
----------------------------

Consider the following program that always deadlocks:

```
void deadlock3() {
  std::mutex m1, m2, m3;
  folly::Baton<> b1, b2, b3;

  auto t1 = std::thread([&m1, &m2, &b1, &b2] {
    std::lock_guard<std::mutex> g1(m1);
    b1.post();
    b2.wait();
    std::lock_guard<std::mutex> g2(m2);
  });

  auto t2 = std::thread([&m3, &m2, &b3, &b2] {
    std::lock_guard<std::mutex> g2(m2);
    b2.post();
    b3.wait();
    std::lock_guard<std::mutex> g3(m3);
  });

  auto t3 = std::thread([&m3, &m1, &b3, &b1] {
    std::lock_guard<std::mutex> g3(m3);
    b3.post();
    b1.wait();
    std::lock_guard<std::mutex> g1(m1);
  });

  t1.join();
  t2.join();
  t3.join();
}
```

Once the process has deadlocked, we can use gdb to find the threads and mutexes involved in the deadlock:

```
$ gdb -p 2174496
(gdb) source -v ./folly/experimental/gdb/deadlock.py
Type "deadlock" to detect deadlocks.
(gdb) deadlock
Found deadlock!
Thread 2 (LWP 2174497) is waiting on mutex (0x00007ffcff42a4c0) held by Thread 3 (LWP 2174498)
Thread 3 (LWP 2174498) is waiting on mutex (0x00007ffcff42a4f0) held by Thread 4 (LWP 2174499)
Thread 4 (LWP 2174499) is waiting on mutex (0x00007ffcff42a490) held by Thread 2 (LWP 2174497)
```

Reviewed By: yfeldblum

Differential Revision: D5860868

fbshipit-source-id: 020a32327a79bb066269fe08113695803ce06c7d

Summary:
We didn't previously benchmark the performance of `get()`, which was a strange
omission.

Reviewed By: akrieger

Differential Revision: D5863567

fbshipit-source-id: 468b249da9120fcb84f3303ac5e2157761b6369d

Summary:
Only for clang for the moment, as more work is needed for GCC.
MSVC builds have always had unused variable warnings enabled, I just hadn't gotten around to cleaning up all of the tests for it to be able to enable it.

Reviewed By: yfeldblum

Differential Revision: D5827840

fbshipit-source-id: ab503b5791fcc58d685b8327179b810880c5dea7

Summary: It was horribly broken in multiple ways. It didn't support input > 4gb on Windows, was truncating the entire table to chars, and simply couldn't be compiled because it was exceeding MSVC's max macro instantion depth of 255.

Reviewed By: yfeldblum

Differential Revision: D5827332

fbshipit-source-id: b08268c88db10c607b27231689b3ee3ec7553c1f

Summary: This makes it now both work, and compile, on Windows.

Reviewed By: yfeldblum

Differential Revision: D5811100

fbshipit-source-id: 5d6bfc04ed8e60417615da15bd197769e0c79c11

fix strange recursive std::is_constructible instantiation involving the Function converting constructor

Summary: In rare and obscure cases, the fact that `folly::Function`'s perfectly-forwarding, implicit converting constructor was SFINAE-ing on the argument's constructibility was causing a recursive template instantiation of std::is_constructible. Switch to passing the argument by value to avoid the need to test for constructibility.

Reviewed By: yfeldblum

Differential Revision: D5847034

fbshipit-source-id: ce2ad1d2490206c6cae84c17544bd9fcd6ff47bb

Summary: Coroutines are only available on MSVC when the /await compiler switch was passed, in which case the `_RESUMABLE_FUNCTIONS_SUPPORTED` macro is defined.

Reviewed By: Orvid

Differential Revision: D5837303

fbshipit-source-id: af3349646e8875e3eac1bc3bbf47203f41f0bbde

Summary:
await_resume is only called once, so this allows it to move the value out.
At the same time remove a redundant clear (but keep the existing requirement that the promise type is an OptionalPromise), and clean up the tests.
Also add a test to make sure the coroutine is cleaned up

Reviewed By: ericniebler

Differential Revision: D5834861

fbshipit-source-id: 7ad487e818969cdf6fe27c9e82931aa247daf4e4

Summary: getAutoUncompressionCodec() currently only allows unambiguous headers. Allow a single "terminal codec" to be called if all other codecs can't uncompress or throw.

Reviewed By: terrelln

Differential Revision: D5804833

fbshipit-source-id: 057cb6e13a48fea20508d5c028234afddf7435f6

Summary:
LTO has better optimization which results in the malloc() being optimized away in this function.

Note we don't use folly::dontOptimizeAway() because
that introduces a circular dependency between the
malloc and benchmark targets.

Reviewed By: marksantaniello, meyering, interwq

Differential Revision: D5840883

fbshipit-source-id: 5dd9b152f70b7a49f125b6d79b4dfa40f4cdac59

Summary:
NoHeap small_vector's no longer require a move constructor.

Also changes const -> constexpr in a bunch of places.

Reviewed By: nbronson

Differential Revision: D5804361

fbshipit-source-id: 0f00fee6d318fa9296612409805d4ffcfbadb974