Summary: We wanted to compare the benefits of using folly::to<std::string> directly, and decided this benchmarking might as well be contributed back to folly.  Here are the results:

```
  ============================================================================
  folly/test/ConvTest.cpp                         relative  time/iter  iters/s
  ============================================================================
  ...
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(1)                                  157.88ns    6.33M
  u64ToStringFollyMeasure(1)                       212.52%    74.29ns   13.46M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(12)                                 158.14ns    6.32M
  u64ToStringFollyMeasure(12)                      212.55%    74.40ns   13.44M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(123)                                152.26ns    6.57M
  u64ToStringFollyMeasure(123)                     210.95%    72.18ns   13.85M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(1234)                               152.40ns    6.56M
  u64ToStringFollyMeasure(1234)                    204.82%    74.41ns   13.44M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(12345)                              156.01ns    6.41M
  u64ToStringFollyMeasure(12345)                   208.90%    74.68ns   13.39M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(123456)                             178.21ns    5.61M
  u64ToStringFollyMeasure(123456)                  238.77%    74.63ns   13.40M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(1234567)                            161.38ns    6.20M
  u64ToStringFollyMeasure(1234567)                 203.09%    79.46ns   12.58M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(12345678)                           159.01ns    6.29M
  u64ToStringFollyMeasure(12345678)                192.42%    82.64ns   12.10M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(123456789)                          169.07ns    5.91M
  u64ToStringFollyMeasure(123456789)               203.70%    83.00ns   12.05M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(1234567890)                         166.56ns    6.00M
  u64ToStringFollyMeasure(1234567890)              187.21%    88.97ns   11.24M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(12345678901)                        176.22ns    5.67M
  u64ToStringFollyMeasure(12345678901)             197.57%    89.20ns   11.21M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(123456789012)                       174.74ns    5.72M
  u64ToStringFollyMeasure(123456789012)            182.52%    95.74ns   10.45M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(1234567890123)                      178.47ns    5.60M
  u64ToStringFollyMeasure(1234567890123)           186.81%    95.54ns   10.47M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(12345678901234)                     187.33ns    5.34M
  u64ToStringFollyMeasure(12345678901234)          184.05%   101.78ns    9.82M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(123456789012345)                    198.16ns    5.05M
  u64ToStringFollyMeasure(123456789012345)         182.48%   108.59ns    9.21M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(1234567890123456)                   182.56ns    5.48M
  u64ToStringFollyMeasure(1234567890123456)        164.19%   111.19ns    8.99M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(12345678901234567)                  186.80ns    5.35M
  u64ToStringFollyMeasure(12345678901234567)       162.33%   115.07ns    8.69M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(123456789012345678)                 195.08ns    5.13M
  u64ToStringFollyMeasure(123456789012345678)      165.51%   117.87ns    8.48M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(1234567890123456789)                200.27ns    4.99M
  u64ToStringFollyMeasure(1234567890123456789)     164.62%   121.65ns    8.22M
  ----------------------------------------------------------------------------
  u64ToStringClibMeasure(12345678901234567890U)              203.18ns    4.92M
  u64ToStringFollyMeasure(12345678901234567890U)   162.38%   125.13ns    7.99M
  ----------------------------------------------------------------------------
  ...
  ============================================================================
```

Reviewed By: yfeldblum

Differential Revision: D2680998

fb-gh-sync-id: 179fbd756c714c92b7230d3750af024865ecbb0a

Summary: Closes https://github.com/facebook/folly/issues/304

Reviewed By: yfeldblum

Differential Revision: D2685289

fb-gh-sync-id: 563697fb01ee358472b9080058848d2b557ba466

Summary: 'flating point' => 'floating point'

Closes https://github.com/facebook/folly/issues/241

Reviewed By: yfeldblum

Differential Revision: D2685280

fb-gh-sync-id: 2e9c2b5419d0c631af4a32c5ab6b7366033ca34c

Summary: Make PthreadKeyUnregister a global singleton for all StaticMeta instances.

Reviewed By: luciang

Differential Revision: D2678401

fb-gh-sync-id: c0d58b483fa6f096b29aeb7df71897a75ea8c892

Summary: This reverts commit 9d355f96c4fe073c889f28070d5952fa4eb007a0.

build-break

Reviewed By: sctaylor

Differential Revision: D2680784

fb-gh-sync-id: a2df233bcd3721ffbfcd6fd71ea3cabbebebd4c4

Summary: D2613681 codemod'ed a thrift server api but it also renamed that api
in AsyncServerSocket, which is a mistake. Fix that in AsyncServerSocket, and
all other places that calls this api.

Reviewed By: alandau, JoelMarcey

Differential Revision: D2677837

fb-gh-sync-id: 0d91f1a623229e99be59ca9dcd27f1330a9a1b64

Summary: Remove unnecessary resetClientHelloParsing callback which causes problems wiht
Openssl 1.0.2

Reviewed By: knekritz

Differential Revision: D2664730

fb-gh-sync-id: d1b55ae493b4c92627ad41e7bf85f1e1a777bd2b

Summary: Remove busy wait from Future::wait.
If future.wait(timeout) has succeded we should
return a ready future, otherwise we should return a future
for the final result (not necessarily ready).

Reviewed By: yfeldblum

Differential Revision: D2646860

fb-gh-sync-id: 62671d09073ad86e84df8c9257e961d2a8c2a339

Summary: Without feedback that a `moveForward` or `moveBackward` did nothing, a user
cannot implement this idiom safely:

```
while(rb.tryRead(entry, cursor)) {
  doSomething(entry);
  cursor.moveBackward();
}
```

In the case where the ring buffer has not overflowed and slot 0 is still
available, the reader will get stuck at it (read it continuously) until
the buffer overflows.

This diff allows the above example to become:

```
while(rb.tryRead(entry, cursor)) {
  doSomething(etnry);
  if (!cursor.moveBackward()) {
    break;
  }
}
```

Reviewed By: bryceredd

Differential Revision: D2674975

fb-gh-sync-id: a0c5857daf186ef19e203f90acc2145590f85c3b

Summary: Clang is too clever and in some contexts optimizes away the `malloc`, but we rely on a side-effect. Declaring the variable as static forces it to call `malloc`. We could free the pointer relying on the fact that the lambda is guaranteed to be called only once, but I feel more comfortable just leaking it (LSan won't complain).

Reviewed By: philippv

Differential Revision: D2674769

fb-gh-sync-id: 1153a3ca226c6b7aa64c453bd61b036dcbf3ffcc

Summary: There's a race between insert() and erase(): as soon as insert()
releases the lock (swaps kLockedKey_ with the actual key), an erase() might
jump in and invalidate the key.

As far as I can tell, this bug existed since the beginning.

Reviewed By: nbronson

Differential Revision: D2673099

fb-gh-sync-id: 4721893d2ad4836e11acc0fb4ecb0dd7b2b69be1

Reviewed By: bmaurer

Differential Revision: D2667499

fb-gh-sync-id: 463f86752240bd88761910de934ba25d6e62fafe

Summary: Inspired by getSocketFromTransport from proxygen.

Reviewed By: siyengar

Differential Revision: D2663937

fb-gh-sync-id: f076215907cd06d6da3de033c57eec8a6a6ce320

Summary: For handling UTF8 strings better.

Reviewed By: yfeldblum

Differential Revision: D1956771

fb-gh-sync-id: e074f9f2c9b472f5e619fef25d8e17296847773c

Summary: [Folly] Simplify some checks by using `__CLANG_PREREQ`.

Reviewed By: meyering

Differential Revision: D2657979

fb-gh-sync-id: 80ff56bbab0e78465d71315b729ad14a09706ed5

Summary: [Folly] Simplify some checks by using `__CLANG_PREREQ`.

Reviewed By: meyering

Differential Revision: D2656842

fb-gh-sync-id: e762fba423fb7cc08907d10dc10f8f46d93a9fe4

Summary: This doesn't make the code less efficient, because RVO can't be used for CollectVariadicContext. Thus moving existing tuple vs constructing new tuple by moving all values from other tuple (where each value is wrapped in folly::Optional) should be pretty much the same.

Reviewed By: hannesr

Differential Revision: D2650293

fb-gh-sync-id: 648a358bf093a0bb9d058a997af9bf59014ad77c

Summary: Add a new method to cork a socket in a persistent manner, instead of the current on-off manner. This is default to false. The liger part of turning this on will be in a separate diff.

I thought about whether I need to turn cork off based on some criteria to alleviate the perf degradation. The obvious things I can think off is just amount of data written as a threshold, or a timeout. But TCP is doing this already for us, unless we want the data threshold to be less than MSS, or we want the timeout to be less than 200ms. THoughts?

Reviewed By: shikong

Differential Revision: D2639260

fb-gh-sync-id: 2821f669c9f72d5ac4c33195bb192fc4110ffe9d

Reviewed By: philippv

Differential Revision: D2643313

fb-gh-sync-id: 10b9f735725ce47fab4bbfaa5972b3863357365f

Reviewed By: Gownta

Differential Revision: D2643850

fb-gh-sync-id: 2c4bb844ea2006215b0637cb1ba08c636faefe05

Summary: Changing the definition of `HHWheelTimer::UniquePtr` wasn't safe, because some clients were using that type outside of the `HHWheelTimer::newTimer` helper. I'm changing that part back. We'll still be able to proceed with my other codemod to `HHWheelTimer`, but we'll always have two different smart pointer types to manage: `UniquePtr` and `IntrusivePtr`.

Reviewed By: djwatson

Differential Revision: D2644721

fb-gh-sync-id: 14685be62355f09d39c4139ef7186d60b5f48dcd

Summary: It never throws.

Reviewed By: pavlo-fb

Differential Revision: D2640886

fb-gh-sync-id: cd643f8847f4bf5619415731484f91fb07116784

Summary: This is probably easier than D2612490. The idea is just to add a callback to write, writev and writeChain in AsyncSocket, so upper layer can know when data starts to buffer up

Reviewed By: mzlee

Differential Revision: D2623385

fb-gh-sync-id: 98d32ca83871aaa4f6c75a769b5f1bf0b5d62c3e

Summary: There have been several ASAN bugs cropping up because the lifetime of an `HHWheelTimer` is not being manager properly. I think that people are too comfortable passing around a raw `HHWheelTimer*` even when it is difficult to prove correctness. The recommended solution used to be to create a `DestructorGuard` every time it was needed. There is enough friction there that not everyone is doing that like they should. We should make resource management easier---as easy as using raw pointers, in fact.

I've fixed the broken copy semantics of `DestructorGuard` and added the operators that allow it to be used as a smart pointer. I added the `IntrusivePtr` helper that can manage an arbitrary derived class of `DelayedDestructionBase`. Now, clients can all safely pass around an `IntrusivePtr` everywhere they used to use a raw pointer. They will get automatic resource management for free.

If you are not convinced that `DestructorGuard` should be changed, then note that the existing behavior is dangerously buggy. Consider the following innocent code that accidentally uses the implicitly-defined copy constructor:
  auto d = DestructorGuard(p);
This results in undefined behavior, because `p` can be accessed after it is destroyed! The bug happens because the default copy constructor copies the raw pointer but doesn't increment the count.

In a separate diff, I'll change all clients who pass around a raw `HHWheelTimer*` to use an `IntrusivePtr<HHWheelTimer>` instead. Then we can even entertain a long-term plan of switching from intrusive pointers to the standard `shared_ptr`.

Reviewed By: djwatson

Differential Revision: D2627941

fb-gh-sync-id: 58a934d64540d0bbab334adc4f23d31d507692da

Summary: My colleague tuomaspelkonen discovered a weird UNSYNCHRONIZED issue a few weeks ago and we ever since stopped using it. Now I finally have some time to root cause it. It turns out UNSYNCHRONIZED unlock the mutex then lock the mutex again, because it copy constructs LockedPtr for overriding the name within the scope, and copy construct locks the mutex again. A one character fix here is to take a reference of LockedPtr instead of copy construct it. However since this is my first time look at the code here, please advise if this is horribly wrong or propose better fix. Also added a test to reproduce the issue without the fix as well as verify the fix.

Reviewed By: yfeldblum

Differential Revision: D2633028

fb-gh-sync-id: a9e8d39b08d4d1265979f8bdaae83619566d10a0

Summary: hg backout -r c9f7b5f3185a
Revert my change (which broke down the cont build t9048692)

Reviewed By: djwatson

Differential Revision: D2640797

fb-gh-sync-id: 51f196ac5a3560fde4dc8fe7bb6ef278d74136e5

Summary: Wait uses baton & callback running baton.post
when the original future is ready. However wrapping baton.post
with a funciton call (preparing a new value) adds the following race: baton.wait wakes up
before that function has call actually finished.
The explanation is the following: to prepare the value of the new future it's necessary
1. baton.post() 2. set the value (move constructor, memory operations, ...)
and this code is executed in a separate thread.
The main idea of this fix is to avoid creating a new future
(whose value is calculated using that 2-step procedure)
and set a callback instead. This callback will be executed when the future is ready and actually
it either will be the last step of promise.setValue or it will run immediately if the future
we are waiting for already contains a value.

Reviewed By: fugalh

Differential Revision: D2636409

fb-gh-sync-id: df3e9bbcc56a5fac5834ffecc63f1bcb94ace02c

Summary: Revert D2632752

Reviewed By: afrind

Differential Revision: D2638974

fb-gh-sync-id: 43d8135421510db7840a99f3c197119a0fd26c09

Summary: Using Clang 3.7, this minimal test program:

  #include <folly/FBString.h>
  struct S { folly::basic_fbstring<char> x; };
  int main(int argc, char *argv[]) {
    S s {};
    return 0;
  }

... breaks with the following error output:

  FBStringTest.cpp:5:8: error: chosen constructor is explicit in copy-initialization
    S s {};
         ^
  ./folly/FBString.h:1009:12: note: constructor declared here
    explicit basic_fbstring(const A& = A()) noexcept {
             ^
  FBStringTest.cpp:3:40: note: in implicit initialization of field 'x' with omitted initializer
  struct S { folly::basic_fbstring<char> x; };

... because this `basic_fbstring` is used in a struct and the struct is being default-constructed.

This patch splits the (nevertheless-correct) one-default-arg constructor into two, to deconfuse clang and have it select the correct constructor to avoid this issue.

Reviewed By: matbd

Differential Revision: D2632953

fb-gh-sync-id: 2c75ae85732678c31543f5cccc73d58317982f07

Summary: The check was originally added to track down cpu pinning issue. In reality the check did get triggered, so change to soft error to calm the crazy nag bot. what's wrong with you.
We need to see the soft error log to find out what the error is.

Reviewed By: mzlee

Differential Revision: D2632752

fb-gh-sync-id: 87c11b186f97f0eb4a6c5ac13a1117b280198673

Summary: Without this tag type, it's impossible to use `Synchronized` with types like:

```
struct A {
  A(int, const char*);
  A(const A&) = delete;
  A& operator=(const A&) = delete;
  A(A&&) = delete;
  A& operator=(A&&) = delete;
};
```

In-place construction solves this problem. Usage:

```
Synchronized a(construct_in_place, 5, "c");
```

Reviewed By: nbronson

Differential Revision: D2610071

fb-gh-sync-id: 251fe8f8f6a2d7484dda64cf04dcacb998145230

Summary: This is the solution for our `HHWheelTimer` crashes, as suggested in D2617966#25.

djwatson also mentioned that maybe there should be some logging in the destructor if there are outstanding callbacks. I couldn't think of anything that would add to the `assert` that already exists in `destroy`. I'm open to suggestions though.

Reviewed By: djwatson

Differential Revision: D2628154

fb-gh-sync-id: f3db6e9384517c9bf3cbb60af8c1e711703a07fa

Summary: Define `__CLANG_PREREQ` macro to check version of clang.

Reviewed By: yfeldblum

Differential Revision: D2630325

fb-gh-sync-id: 3d666e554e8ddfc2c1fecd439aaf93f015829025

Summary: Callbacks sometimes outlive the `HHWheelTimer` that they reference. Then the `Callback` tries to reference the dead `HHWheelTimer` and it could either misbehave or crash. This was caught reliably by ASAN tests.

Since `HHWheelTimer` already supports intrusive ref counting, the solution is to acquire a reference within the `Callback`.

Reviewed By: djwatson

Differential Revision: D2617966

fb-gh-sync-id: 02be9ffc5851c269d5933288a17ad394b33ac2dd

Summary: Do not cancel TimeoutHandler timeout if the timeout has already run.

Reviewed By: spalamarchuk

Differential Revision: D2622280

fb-gh-sync-id: 27d83b44ab225e2859695f4e5f21cef934824a35

Summary: This name's meaning is very obscure, this method actually sets the
queue size of each acceptor and if all acceptor's queues are full the
connection will be dropped. Change it to a more meaningful name.

Reviewed By: alandau

Differential Revision: D2613681

fb-gh-sync-id: baa374cdf0a87c460df3dd5687e3d755b55f4b4f

Summary: Start server timeout after socket write succeeds in mcrouter.  Add neceessary Fibers logic to enable this behavior.

Reviewed By: pavlo-fb

Differential Revision: D2613344

fb-gh-sync-id: 1bc0fbe8b325a3e91cd010f89104b83ebf183679

Summary: If SharedPromise::getFuture() is invoked after a call to setInterruptHandler,
then the interrupt handler isn't set on the newly created promise. This diff
fixes that.

Reviewed By: yfeldblum

Differential Revision: D2610289

fb-gh-sync-id: bf8fce9e881b83ccac17d13c6788ec2afd0b0153

Summary: Allows AsyncTransportWrapper's to supply the underlying application
protocol being used, for example using NPN for SSL or some other
generic protocol indication mechanism.

Reviewed By: ranjeeth

Differential Revision: D2614179

fb-gh-sync-id: 2079782bb7d44f898fb14c7df15077209b022424

Summary: Our use case need to have the IndexType Configurable, but in this diff D2583752, lint error shows
  Code from folly::detail is logically private, please avoid use outside of folly.
In order to fix this lint error, I switch the IndexType and Allocator in the AtomicUnorderedInsertMap template.

Reviewed By: nbronson

Differential Revision: D2610921

fb-gh-sync-id: ae81b41e7c8c971f26c61b8c67dabeadff379584