Summary:
Use tag dispatching instead of `enable_if`: it is clearer, it
sidesteps the GCC mangling bug, and more importantly the conditional
doesn't leak into the symbol, making stack traces and profiles more
readable.

Testing on a compilation unit with 1000 `Function`s from simple lambdas.
Before:
```
folly::impl::Function<int (), false>::Function<main::{lambda()#1}, {lambda()#1}>(main::{lambda()#1}&&, std::enable_if<std::integral_constant<bool, ((sizeof (std::decay<main::{lambda()#1}>::type))<=(sizeof folly::detail::function::Data::small))&&std::is_nothrow_move_constructible<std::decay<main::{lambda()#1}> >::value>::value, folly::detail::Tag>::type)::Ops::call(folly::detail::function&)
```
After:
```
folly::impl::Function<int (), false>::OpsSmall<main::{lambda()#1}>::call(folly::detail::function::Data&)
```
Note that the function type is repeated 5 times before, and only once after. This makes a large difference with long namespaces.

Binary size is almost unaffected, compile times slightly better:
Before:
GCC opt: 22.3 seconds, 4435232 bytes
Clang dev: 7.7 seconds, 5257344 bytes

After:
GCC opt: 18.6 seconds, 4493920 bytes
Clang dev: 7.2 seconds, 5469136 bytes

Reviewed By: ericniebler

Differential Revision: D3231530

fb-gh-sync-id: 6aa76e7f780a8afdbfed8a378f257ceb86dce704
fbshipit-source-id: 6aa76e7f780a8afdbfed8a378f257ceb86dce704

Summary: there is no need to call `std::function::invoke` for every DestructorGuard.

Reviewed By: yfeldblum

Differential Revision: D3229345

fb-gh-sync-id: c42f8cd05576d56b6a9b2f9d06878d9b01a36e94
fbshipit-source-id: c42f8cd05576d56b6a9b2f9d06878d9b01a36e94

Summary:
Just like the real thing does.
This was causing some issues when trying to link against glog, which expects the flags to be namespaced like this.

Reviewed By: mzlee

Differential Revision: D3230630

fb-gh-sync-id: a73ab3044560d561a39eb91ceee1588c147a46c5
fbshipit-source-id: a73ab3044560d561a39eb91ceee1588c147a46c5

Summary:
folly::Function is causing significant compile time regressions. Reimplement it in a simpler way.

These are the times for a file containing 1000 instantiations of folly::Fuction (old), folly::Function (new), and std::function with **g++ 4.8 -O3** on my CentOS7 server.

|        | Old `folly::Function` | `std::function` | New `folly::Function` |
|--------|-----------------------|-----------------|-----------------------|
| Time   | 10m37s                | 0m16.81s        | 0m14.75s              |

And for the executable size:

|        | Old `folly::Function` | `std::function` | New `folly::Function` |
|--------|-----------------------|-----------------|-----------------------|
| Size   | 10,409,504            | 732,150         | 562,781               |

That's a **43X** improvement in compile times and an **18X** reduction in executable bloat over the old implementation.

The times for **clang (trunk)** are very different:

|       | Old `folly::Function` | `std::function` | New `folly::Function` |
|-------|-----------------------|-----------------|-----------------------|
| Time  | 4m6s                  | 0m45.27s        | 0m11.78s              |

That's a **20X** improvement over the old implementation and almost a **4X** improvement over `std::function`.

For **gcc-5.3.0**, compile times are again different:

|       | Old `folly::Function` | `std::function` | New `folly::Function` |
|-------|-----------------------|-----------------|-----------------------|
| Time  | 2m49s                 | 0m18.99s        | 0m20.70s              |

With gcc-5.3, the new implementation "only" compiles 8x faster than the old one, and is roughly the same as `std::function`.

Reviewed By: spacedentist, ot, luciang

Differential Revision: D3199985

fb-gh-sync-id: b97982a9dc3a63140510babea34988932e89f2d9
fbshipit-source-id: b97982a9dc3a63140510babea34988932e89f2d9

Summary: Without this, malicious inputs can crash anything using folly::parseJson.

Reviewed By: yfeldblum

Differential Revision: D3219036

fb-gh-sync-id: 3604a060170c0201473c420035b21b018383789c
fbshipit-source-id: 3604a060170c0201473c420035b21b018383789c

Summary: Remove dead code in AsyncSSLSocket.

Reviewed By: knekritz

Differential Revision: D3226948

fb-gh-sync-id: e85823f311de2539c6aa2d6bcc3ff3aee07045bf
fbshipit-source-id: e85823f311de2539c6aa2d6bcc3ff3aee07045bf

Summary: This bug causes failure when the test is run under ASAN.

Reviewed By: meyering

Differential Revision: D3229494

fb-gh-sync-id: a43c8332cc45f7892ac86cd0abb799616bca7779
fbshipit-source-id: a43c8332cc45f7892ac86cd0abb799616bca7779

Summary: no need in virtual call from EventHandler.

Reviewed By: yfeldblum

Differential Revision: D3226960

fb-gh-sync-id: eb9c191630e1a1ac022666201100e3778eb7b611
fbshipit-source-id: eb9c191630e1a1ac022666201100e3778eb7b611

Summary:
'get' is the most frequent memcached operation. On a get reply, we should go to heap
as little as possible.  This diff optimizes for this scenario, where replies
have only one IOBuf field.

Reviewed By: pavlo-fb

Differential Revision: D3226592

fb-gh-sync-id: 92e1a1fac5735bd268691cf11990a96ae6fa8309
fbshipit-source-id: 92e1a1fac5735bd268691cf11990a96ae6fa8309

Summary:
Currently UTF8Range has a constructor that allows you construct an object of type UTF8Range using only an object of type folly::Range. Adding a constructor so that we can construct an UTF8Range object using a std::string.

Currently,
  void sampleMethod(UTF8StringPiece sp) {...}
  /*
  ...
  */
  std::string str = "example";
  folly::UTF8Range utf8Range(str);
  folly::StringPiece sp(str);
  sampleMethod(utf8Range); // works
  sampleMethod(sp); // works
  sampleMethod(str); // doesn't work

This diff hopes to fix this issue.

Reviewed By: ddrcoder

Differential Revision: D3221144

fb-gh-sync-id: dd6ec4d7790d4602dccb3b63a4861d358aed3608
fbshipit-source-id: dd6ec4d7790d4602dccb3b63a4861d358aed3608

Summary: same as D3156698, without changes in Cpp2Connection (which was the only real change in the diff)

Reviewed By: haijunz

Differential Revision: D3222792

fb-gh-sync-id: 245c7add837c0fc6d0bc84aa7d80b929ba2ce386
fbshipit-source-id: 245c7add837c0fc6d0bc84aa7d80b929ba2ce386

Summary: If we don't, then anywhere we include `glog/logging.h` after the portability header will get the `DECLARE_*` and `DEFINE_*` macros undefined -_-....

Reviewed By: mzlee

Differential Revision: D3220797

fb-gh-sync-id: 52907ddcd6b222fb1c6423034ea999eac5ce09ab
fbshipit-source-id: 52907ddcd6b222fb1c6423034ea999eac5ce09ab

Summary: This dependency is in the wrong order.

Reviewed By: knekritz

Differential Revision: D3224312

fb-gh-sync-id: 98d2c58b75cf5f16892d462ae1b877d06bce3faa
fbshipit-source-id: 98d2c58b75cf5f16892d462ae1b877d06bce3faa

Summary: Why not kill fbstring entirely? There are some legitimate use cases. For example, `folly::IOBuf` supports `moveToFbstring()` method which is impossible to implement with `std::string`.

Reviewed By: joeg, snarkmaster

Differential Revision: D3189410

fb-gh-sync-id: 9bb9090ca6012ac32ba9fb79041b26ec4888781f
fbshipit-source-id: 9bb9090ca6012ac32ba9fb79041b26ec4888781f

Summary:
Retire `BOOST_STATIC_ASSERT` in favor of `static_assert`.

`static_assert` is part of C++ now, so we don't need workarounds like `BOOST_STATIC_ASSERT` anymore.

Partially automated:

    hg grep -lw BOOST_STATIC_ASSERT | xargs perl -pi -e 's~\bBOOST_STATIC_ASSERT\(([^;]*)\);~static_assert(\1, "");~g'
    hg grep -lw 'boost/static_assert.hpp' | xargs perl -pi -e 's,^#include <boost/static_assert\.hpp>\n,,gm'

Caught most instances. Formatting and remaining instances addressed manually.

Reviewed By: meyering

Differential Revision: D3215944

fb-gh-sync-id: f4552d5d9bfc416ce283923abe880437a4d0cba5
fbshipit-source-id: f4552d5d9bfc416ce283923abe880437a4d0cba5

Summary: This assignment is unnecessary, because in `for` loop we **always** call `cloneOneInto` that would assign another IOBuf to that IOBuf.

Reviewed By: alikhtarov

Differential Revision: D3215861

fb-gh-sync-id: ad87b99848aaae79f0870d49e0474f1abf0f28e5
fbshipit-source-id: ad87b99848aaae79f0870d49e0474f1abf0f28e5

Summary:
Had this in another diff, but it caused too much test noise. So I've separated
it out on it's own.

Reviewed By: yfeldblum

Differential Revision: D3213605

fb-gh-sync-id: 9ebfcf8430da7c66a31868032a0cef1e616ffc58
fbshipit-source-id: 9ebfcf8430da7c66a31868032a0cef1e616ffc58

Summary:When dealing with universal references, std::move will move from
objects that are passed as lvalue references. Instead std::forward
should be used, which only moves from an object if it's passed
as rvalue reference.

Reviewed By: yfeldblum

Differential Revision: D3200402

fb-gh-sync-id: 14be071e8498dd64cb8b2583c0cc2dd383bfebb8
fbshipit-source-id: 14be071e8498dd64cb8b2583c0cc2dd383bfebb8

Summary:It's been awhile.

Still has intern URLs (#10943549) but I'll fix that separately.

Reviewed By: jsedgwick

Differential Revision: D3213245

fb-gh-sync-id: ff60193ff368deaac8ca233d4289f30d8f6bb223
fbshipit-source-id: ff60193ff368deaac8ca233d4289f30d8f6bb223

Summary:Instead of std::function<bool(int, int)>, use folly::Function to
pass callbacks to Subprocess::communicate. This makes it possible
to pass non-copyable callables, which is especially interesting
because Subprocess::readLinesCallback returns a non-copyable
object.

This diff also fixes the forwarding of the callback passed to
readLinesCallback in case you pass an lvalue reference.

Reviewed By: snarkmaster

Differential Revision: D3169956

fb-gh-sync-id: 7a906f9a3ab50502fc04e0d83a23ca5e0201bb3e
fbshipit-source-id: 7a906f9a3ab50502fc04e0d83a23ca5e0201bb3e

Summary:[Folly] `get_default` and `get_ref_default` variants taking functions.

Useful if the default value is computationally expensive to construct or requires IO.

Reviewed By: andriigrynenko, spacedentist

Differential Revision: D3189247

fb-gh-sync-id: 51c64293f8712d7590348d53cbfd892a5efd9e82
fbshipit-source-id: 51c64293f8712d7590348d53cbfd892a5efd9e82

Summary: The signals were represented using bytes in a pipe or using a count on an event fd (when available). This count was ever growing and caused the pipe to overflow, and in both cases you would get signals on empty queues. This diff only writes to the fd if it there are no bytes to read. Due to races there can still be multiple bytes in the pipe, but overflowing should not be possible. Instead of blindly signaling when there could be messages in the queue, the signals are now synchronized with the state of the queue so that the signals are drained when the queue is empty. This also made it possible to skip the semaphore behavior of the event fd which should improve perf.

Reviewed By: dcolascione

Differential Revision: D3198252

fb-gh-sync-id: 39e620b10c254ffcacabc4c5ac36950a215d4803
fbshipit-source-id: 39e620b10c254ffcacabc4c5ac36950a215d4803

Summary: as titled. When I tried re-adding all functions after cancelAllFunctions, it throws error. This is because it doesn't reset currentFunction to null.

Reviewed By: jjs0

Differential Revision: D3209237

fb-gh-sync-id: 5b6e2d967fc3c0986320d23b8d61eb1bfbff8940
fbshipit-source-id: 5b6e2d967fc3c0986320d23b8d61eb1bfbff8940

Summary: Closes https://github.com/facebook/folly/pull/401

Reviewed By: yfeldblum

Differential Revision: D3207682

Pulled By: snarkmaster

fb-gh-sync-id: 617aeec0e6fe1f46d2464df4b72a3e91c953dc12
fbshipit-source-id: 617aeec0e6fe1f46d2464df4b72a3e91c953dc12

Summary: Add more compatibility for missing gflags

Reviewed By: yfeldblum

Differential Revision: D3202560

fb-gh-sync-id: d25e4abfe8ceee9fb329c9ba12d259d1d03d4974
fbshipit-source-id: d25e4abfe8ceee9fb329c9ba12d259d1d03d4974

Summary: these macros are generally useful for other higher-order macros

Reviewed By: yfeldblum

Differential Revision: D3194777

fb-gh-sync-id: 667fc51c681786ad422309ee463881dc22c972f7
fbshipit-source-id: 667fc51c681786ad422309ee463881dc22c972f7

Summary:Clean up a deprecation warning for JSONSchema's use of
Singleton. This is in experimental, so the interface change should be
reasonable..

Reviewed By: agoder

Differential Revision: D3203348

fb-gh-sync-id: 3283c7d9c507a545f3217eb5afc3734eb047b833
fbshipit-source-id: 3283c7d9c507a545f3217eb5afc3734eb047b833

Summary: find replace 's/{([0-9, a-z"-]+)}/dynamic::array(\1)/g'

Reviewed By: agoder

Differential Revision: D3203454

fb-gh-sync-id: 064bb2bdd0e19a80da32e8f4eb730fc4268d7cad
fbshipit-source-id: 064bb2bdd0e19a80da32e8f4eb730fc4268d7cad

Summary:There're currently two ways to set RequestContext
- RequestContext::create() - creates new context and sets it
- RequestContext::setContext(context) - sets context previously captured by saveContext
In most cases, the RequestContext is set back after the request is processed but sometimes it's not (especially with RequestContext::create). We want to measure cpu time for a request by measuring the total cpu time when a RequestContext is set, so we need to make sure that it's properly reset after the thread is done with the request. Scope guards can help us with that.

Reviewed By: haijunz

Differential Revision: D3156698

fb-gh-sync-id: 7c3eb06c1cc27849071625011bf64c5ad36c0612
fbshipit-source-id: 7c3eb06c1cc27849071625011bf64c5ad36c0612

Summary: Before this fix, the callback would silently ignore `ret == -1` if the error isn't `EAGAIN`.

Reviewed By: spacedentist

Differential Revision: D3193845

fb-gh-sync-id: e4a7aa37de7dab8ebe0633dd9888d8adc11dd1c2
fbshipit-source-id: e4a7aa37de7dab8ebe0633dd9888d8adc11dd1c2

Summary: `__attribute__((no_sanitize("address")))` is not valid in clang 3.6 and earlier

Reviewed By: skotchvail

Differential Revision: D3197412

fb-gh-sync-id: bd555b030fe48268988299dd88b9b7aea54c1a73
fbshipit-source-id: bd555b030fe48268988299dd88b9b7aea54c1a73

Summary: ^^^ this is a stack overflow in the test, and a possible stack or heap overflow.

Reviewed By: dcolascione

Differential Revision: D3151717

fb-gh-sync-id: b4f0660ebbb89139dff003870e132c312068d9a8
fbshipit-source-id: b4f0660ebbb89139dff003870e132c312068d9a8

Summary: This function is being proposed in WG21, the C++ standards body for inclusion in the STL via the Library Fundamentals v2 TS. Using the normal constructor for a std::array with an initializer list introduces a source of coupling between the # of elements you put in the initializer list and the size of the array you specify as a template argument. Worse still, if you put less things in the initializer list than the template argument specifies, it doesn't warn you that you've probably made a pretty devious and subtle error. With this function your array size will always be the same as the # of things you actually put in it. What's more, in some cases this can deduce the type of the elements as well.

Reviewed By: yfeldblum

Differential Revision: D3164432

fb-gh-sync-id: beceaae2ee01cd5f93dec86cf36efdb78a28b4a3
fbshipit-source-id: beceaae2ee01cd5f93dec86cf36efdb78a28b4a3

Summary:There're currently two ways to set RequestContext
- RequestContext::create() - creates new context and sets it
- RequestContext::setContext(context) - sets context previously captured by saveContext
In most cases, the RequestContext is set back after the request is processed but sometimes it's not (especially with RequestContext::create). We want to measure cpu time for a request by measuring the total cpu time when a RequestContext is set, so we need to make sure that it's properly reset after the thread is done with the request. Scope guards can help us with that.

Reviewed By: haijunz

Differential Revision: D3156698

fb-gh-sync-id: cfb678531810e8be5faaf02cb7803bd247557e42
fbshipit-source-id: cfb678531810e8be5faaf02cb7803bd247557e42

Summary: Add some logging to figure out the state of the Qeueu when the write error happens.

Differential Revision: D3190882

fb-gh-sync-id: 6515d77df8aa3086922cb4053f2e437f3e527a36
fbshipit-source-id: 6515d77df8aa3086922cb4053f2e437f3e527a36

Summary:folly::fibers does not use folly::MoveWrapper anymore, so no need to
include that header file.

Reviewed By: yfeldblum

Differential Revision: D3169374

fb-gh-sync-id: 2409b46156843fb0a1454b560c42186f1c412988
fbshipit-source-id: 2409b46156843fb0a1454b560c42186f1c412988

Summary:This is the last place in folly that uses MoveWrapper (other than
the MoveWrapper implementation itself and its tests, of course).

Instead of using a MoveWrapper, the object in question is moved
into the lambda using C++14 syntax, and the lambda is moved in a
call to EventBase::runInEventBaseThread which is possible now
that the EventBase methods accept non-copyable callbacks.

Reviewed By: yfeldblum

Differential Revision: D3169316

fb-gh-sync-id: 2dcb1a523ac417f4619c607898e58b572648e3da
fbshipit-source-id: 2dcb1a523ac417f4619c607898e58b572648e3da

Summary:Renamed AtomicLinkedList to AtomicIntrusiveLinkedList.
AtomicLinkedList is a simple AtomicIntrusiveLinkedList wrapper, which handles intrusive list hook.

Reviewed By: yfeldblum

Differential Revision: D3188171

fb-gh-sync-id: 0823b04a48336d65e0a6a8cd412c75f52afe02b9
fbshipit-source-id: 0823b04a48336d65e0a6a8cd412c75f52afe02b9

Summary:9ab69bc7 removed `__APPLE__` around the strndup definition
because it is defined on modern OSX.  But there was another reference
in String.cpp. Fixing that.

Reviewed By: yfeldblum

Differential Revision: D3186360

fb-gh-sync-id: 709c3b93cd22945e2237412637929df1979526c1
fbshipit-source-id: 709c3b93cd22945e2237412637929df1979526c1

Summary:Although, according to the manpage, these functions are defined in `strings.h`, but they are also defined in `string.h`. We never actually use these functions via `strings.h`, and instead only ever reference them via `string.h`.
To keep things sane, lets just move the functions into `string.h` and kill `strings.h`.

Reviewed By: yfeldblum

Differential Revision: D3181596

fb-gh-sync-id: 8a474df510ddafc4c595b08b809a7c33e3256177
fbshipit-source-id: 8a474df510ddafc4c595b08b809a7c33e3256177