Summary:
Create pipe-adapters ("pipe fittings") that allow a `|`-based pipeline mixing {std-containers and/or range-v3} with folly::gen, e.g.,

```
auto result = myVec              // anything consistent with range-v3 or these adapters
    | ranges::view::filter(...)  // zero-or-more range-v3 pipe-elems
    | <adapter-goes-here>        // <==**one of the pipe-adapters provided by this task**
    | folly::gen::blah();        // trailing pipe-elems are folly::gen
```

This diff supplies only adapters that transition from {std-containers and/or range-v3} to folly::gen, but not the other way around.

Q&A:

* Why distinguish containers from range-v3's? E.g., container_to_gen vs. rangev3_to_gen?
    * Containers and range-v3's have different copy-costs: range-v3's have O(1) copy
    * Using two different names lets us separate the implementations so we can know which can be copied without significant overhead.
* Why `#include` range-v3 from inside folly::gen? Why the dependency?
    * That `#include` / dependency adds value to the process, and it is included only for the client-files that need it.
    * It adds value to the process since the subset of client-files to be migrated are precisely the same subset of client-files that _need_ to include range-v3.
    * The alternative would be to add the `#include` out in all the various client-files during the migration process, and we will do that as the last step in the migration process.
    * The migration process is sped up by including range-v3 for that specific subset of client-files _and_ it hurts no one since only those who need that `#include` actually get it.
    * Note: we limit the `#include` to the subset of files to be migrated via the `FOLLY_USE_RANGEV3` define; see folly-config.h.

Reviewed By: yfeldblum

Differential Revision: D15035294

fbshipit-source-id: 694979850d1f35dd382e3afde792ea51a2397af0

Summary:
Change the EventBaseTest code to request precise timing from libevent.
libevent 2.1+ uses a coarse monotonic clock by default on Linux.
This causes several of folly's timing-related tests for EventBase to fail most
of the time.

This changes the tests to request precise timing from libevent2, using the
`EVENT_PRECISE_TIMER`.  While we can request this programmatically, doing so
portably across libevent versions is awkward, so the environment variable is
the easiest solution for now.

Alternatively we could change the tests to use larger, coarser timeouts to
make them pass reliably.  However, this would make the tests slower.

Differential Revision: D15528322

fbshipit-source-id: 20dc55de36235e63910cf7fb5b67c6f2d509cc15

Summary: Put file-local classes and helper functions into an unnamed namespace.

Reviewed By: yfeldblum

Differential Revision: D15528323

fbshipit-source-id: 9e90aafe4382d9ba237823fea1e68dbea7fa1f2f

Summary: [Folly] Fix references to `TTransportException` in `folly/io/async/` to refer to `AsyncSocketException`.

Reviewed By: jmswen, knekritz

Differential Revision: D15628173

fbshipit-source-id: f6d36ede5e8b33d9407751733bcc9a7fa764815c

Summary:
- Clang 8 warns about appending integers to a string using `operator+`
  without a cast.

```
../folly/test/FixedStringTest.cpp:353:23: warning: adding 'unsigned int' to a string does not append to the string [-Wstring-plus-int]
  a.append("X world!" + 2u, 5u);
           ~~~~~~~~~~~^~~~
../folly/test/FixedStringTest.cpp:353:23: note: use array indexing to silence this warning
  a.append("X world!" + 2u, 5u);
                      ^
           &          [   ]
../folly/test/FixedStringTest.cpp:354:23: warning: adding 'unsigned int' to a string does not append to the string [-Wstring-plus-int]
  a.append("X world!" + 7u);
           ~~~~~~~~~~~^~~~
../folly/test/FixedStringTest.cpp:354:23: note: use array indexing to silence this warning
  a.append("X world!" + 7u);
                      ^
           &          [   ]
../folly/test/FixedStringTest.cpp:365:23: warning: adding 'unsigned int' to a string does not append to the string [-Wstring-plus-int]
  a.append("X world!" + 2u, 5u);
           ~~~~~~~~~~~^~~~
../folly/test/FixedStringTest.cpp:365:23: note: use array indexing to silence this warning
  a.append("X world!" + 2u, 5u);
                      ^
           &          [   ]
../folly/test/FixedStringTest.cpp:366:23: warning: adding 'unsigned int' to a string does not append to the string [-Wstring-plus-int]
  a.append("X world!" + 7u);
           ~~~~~~~~~~~^~~~
../folly/test/FixedStringTest.cpp:366:23: note: use array indexing to silence this warning
  a.append("X world!" + 7u);
                      ^
           &          [   ]
```

- Fix this warning by creating a local char[] and using that to append
  to the fixed string
Pull Request resolved: https://github.com/facebook/folly/pull/1148

Reviewed By: ericniebler

Differential Revision: D15618465

Pulled By: yfeldblum

fbshipit-source-id: 7f72b3597f51d99665da85744aeb8805eb2e8f00

Summary: [Folly] Fix `PriorityUnboundedBlockingQueue` priority translation from `Executor` priorities to offsets as used by `PriorityUnboundedBlockingQueueSet`.

Reviewed By: andriigrynenko

Differential Revision: D15619435

fbshipit-source-id: 1c5d4d68dfde7f9db07d64f40e73717b48a05ed1

Summary: If performRead is called with bufLen > 2GB then overflow occurred with the value passed to SSL_read.  We'll clamp it here. This should be fine since performRead will be called again as there is more data to read.

Reviewed By: andriigrynenko, knekritz, mingtaoy

Differential Revision: D15625000

fbshipit-source-id: 8633686a76baebd796139f3b20c6f7286339fd96

Summary: Exposed by D15610738.

Reviewed By: ngoyal

Differential Revision: D15622920

fbshipit-source-id: f3058c69098ae740d43f27e8161e99b3c5a6b995

Summary:
The main change is to grab a wlock in doSetContextData, which enables to make the code more readable, and (insignificantly) more efficient.

Grabbing the wlock directly is also strictly better for both `set` and `override`.
`setIfAbsent` is the only one to potentially suffers from the lock change, in the case where it already exists. But `setIfAbsent` isn't used by either of the guards, which are the recommended way of changing values in RequestContext. So it seems incorrect to optimize for it, and overkill to fork the code.

Reviewed By: yfeldblum

Differential Revision: D15604768

fbshipit-source-id: 44f564b09ff50e8bfe0e1c4cf5ee2d77b654e929

Summary: A very basic function that if done incorrectly will get optimized away as undefined behavior. For now keep things simple and only support addition of unsigned values.

Reviewed By: yfeldblum

Differential Revision: D15609542

fbshipit-source-id: 70d5fde784f57d3d52e6122352a885d7a835f104

Summary: [Folly] Fix SerialExecutor task destruction order where tasks are destroyed outside of the request-context scope.

Reviewed By: andriigrynenko

Differential Revision: D15618395

fbshipit-source-id: e2ec8e42137d14f549f92dbc96a904eadcc0a587

Summary:
A couple of changes to support building folly in MSVC/win32 for x86 and arm platforms.
Pull Request resolved: https://github.com/facebook/folly/pull/1147

Reviewed By: Orvid

Differential Revision: D15592309

Pulled By: yfeldblum

fbshipit-source-id: 97860ab9309e5492bfadac56079af735741d4a2c

Reviewed By: yfeldblum

Differential Revision: D15610738

fbshipit-source-id: 367919db6465536e215735400652d33290930ca0

Summary:
There are two variants of `strerror_r` function, one returns
`int`, and another returns `char*`. Selecting proper version using
preprocessor macros portably is extremely hard.

For example, on Android function signature depends on `__USE_GNU` and
`__ANDROID_API__` macros (https://git.io/fjBBE).

So we are using C++ overloading trick: we pass a pointer of
`strerror_r` to `invoke_strerror_r` function, and C++ compiler
selects proper function.

Reviewed By: yfeldblum

Differential Revision: D15484722

fbshipit-source-id: fc0bd45fa67dc401631ffc185c9fad231e4a48a0

Summary: Title, unecessary cost in case of conflict

Reviewed By: yfeldblum

Differential Revision: D15604536

fbshipit-source-id: ad40c84b822a96a688f810b24b539ac162fdcc59

Summary:
As part of trying to get our internal usage of folly off a fork, we have various compiler warnings set ridiculously high.

This gets rid of a couple of warnings that we hit in folly code.
Pull Request resolved: https://github.com/facebook/folly/pull/1145

Reviewed By: LeeHowes, Orvid

Differential Revision: D15586209

Pulled By: yfeldblum

fbshipit-source-id: dc3ebffbddd0b82f2c2ee719a95b7fcfe551e074

Summary: swap the order of getLocalAddress() and getPeerAddress(), so we are more likely to log the local address after exception happens.

Reviewed By: knekritz

Differential Revision: D15559814

fbshipit-source-id: 50b7a964d6c3add2e4ae1da9fde8e9e4e67e5715

Summary:
Grabbing the mutex of the newly created context is unecessary cost.
folly::Synchronized's constructor support this optimization, so it's an easy change.

Reviewed By: yfeldblum

Differential Revision: D15600165

fbshipit-source-id: e92570a7ac7ac1e908d7c797bed6de22f940d387

Summary:
The shallow copy code path currently iterates and copies all values manually. Instead of benefiting from the underlying data collection's implementation of self-copy.
At the very least, it's simpler looking code.

Inheriting unique_ptr is usually discouraged, but in this specific (internal impl detail) use case, I can't foresee any risk.

Reviewed By: yfeldblum

Differential Revision: D15599260

fbshipit-source-id: 73edea27a27e8fbc8b057cf3e974ee3d83a6e760

Summary: Pull Request resolved: https://github.com/facebook/folly/pull/1141

Reviewed By: LeeHowes

Differential Revision: D15560029

Pulled By: yfeldblum

fbshipit-source-id: 5f0d5ee8d09be834d1216d4c39244e0855d2dc0f

Summary:
- Old versions of GCC (specifically, GCC 4.7) warn about uninitialized memory
  in `Expected.h`
- Newer versions of GCC do not complain, so remove the pragma push/pop which
  was disabling the warning.
Pull Request resolved: https://github.com/facebook/folly/pull/1143

Reviewed By: ericniebler

Differential Revision: D15586279

Pulled By: yfeldblum

fbshipit-source-id: 7b01934c7601ecf035f1e05f2ed3e5f799cf25b9

Summary:
This can be used to check if ChaCha20 is available for use.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

related: https://github.com/facebookincubator/fizz/pull/27
Pull Request resolved: https://github.com/facebook/folly/pull/1146

Reviewed By: knekritz

Differential Revision: D15583706

Pulled By: yfeldblum

fbshipit-source-id: 1195d623098018992811cd7d6cef72e2366ace19

Summary: [Folly] Fix a regression in per-task allocations in `SerialExecutor`.

Reviewed By: andriigrynenko

Differential Revision: D15589007

fbshipit-source-id: 4461798435833cb317b41cfea932762eb7ac8662

Summary: [Folly] Cut outdated comment in `F14Table`, referring to the return value of a function which returns `void`.

Reviewed By: nbronson

Differential Revision: D15586980

fbshipit-source-id: b75f7b989c39b52e589ce8051663085201939433

Summary: [Folly] Move `SerialExecutor` test-specific helper types into the tests which need them.

Reviewed By: andriigrynenko

Differential Revision: D15587721

fbshipit-source-id: 603e5381b2e00b4317f7e9836c6102238158c5d0

Summary: Pull Request resolved: https://github.com/facebook/folly/pull/1142

Reviewed By: shixiao

Differential Revision: D15574540

Pulled By: yfeldblum

fbshipit-source-id: 2ce91f7510f0b278677c15b3a9f1f80b43ff8998

Summary:
SerialExecutor can not rely on parent to save RequestContext for him as it is not guaranteed that an enqueued function will be executed from the parent callback that was scheduled at the same time.
This diff captures RequestContext in a lambda and sets it correctly

Reviewed By: shixiao

Differential Revision: D15381223

fbshipit-source-id: 9b3ab1f96e57eb5e697efb52105d80c2899a03e7

Summary: Lock elision requires non-mutating functions that check if lock acquisition could succeed. This diff adds such functions to folly::SharedMutex, including eligible_for_lock_elision(), eligible_for_lock_upgrade_elision(), and eligible_for_lock_shared_elision(). The diff also adds assertions to validate these functions' correctness under single-threaded executions.

Reviewed By: nbronson

Differential Revision: D15545398

fbshipit-source-id: 0037d473c9dd360f7143ea4c4c9092fb9bb7f5f9

Summary: Acquiring a lock into an unused temporary is generally a bug. Anyone wanting to do this can suppress their compiler's warning by explicitly `static_cast`ing the lock holder to void.

Reviewed By: vitaut

Differential Revision: D15504563

fbshipit-source-id: 1033f6a1d4044b9698934b73eefebfe83602a2a5

Summary:
[Folly] Use a M:N caches-to-lifetimes in `SingletonThreadLocal`.

Sometimes the compiler will not merge cache and lifetime thread-local variables in expected ways, so be resilient. More details in #1135 and https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90562.

At the same time, move the tracking into the wrapper. The lifetime was an intrusively-linked-list node which was clever and which was allocation-free but which increased the TLS requirement per instantiation of `SingletonThreadLocal`. Moving the tracking into the wrapper decreases the TLS requirement, although the tracking now requires heap allocations.

Fixes #1135.
Closes #1138.

Reviewed By: andriigrynenko

Differential Revision: D15508024

fbshipit-source-id: a344e8dd52bd52724ad85b0fc88d6a2a349952ac

Summary: The cacheline padding in folly/test/SharedMutexTest is not actually functional since the compiler is free to rearrange and optimize away local variables. This diff fixes the cacheline padding by aligning the false-sharing critical values.

Reviewed By: nbronson

Differential Revision: D15523241

fbshipit-source-id: c51b1e4cd78ab33f75fa93faf0a0346ec602f97c

Summary:
[Folly] Move executor to local var immediately in `doCallback`, and always move it into the callback.

(Note: this ignores all push blocking failures!)

Reviewed By: andrewcox

Differential Revision: D15532854

fbshipit-source-id: 971a6a64ad3c47c9f5e9f75907a568f9d59b1000

Summary:
- Replace some calls sites from `NDEBUG` to `kIsDebug`.
- Not every call site is changed; there are a few useful cases of
  `NDEBUG` still. `xlog` macros are one of them. Another is where we
  conditionally define a variable in a local scope and then use it in an
  `assert`.
Pull Request resolved: https://github.com/facebook/folly/pull/1128

Reviewed By: aary

Differential Revision: D15490848

Pulled By: yfeldblum

fbshipit-source-id: 4f2d1689f90baa25d3ba9e99a2a388d9cfc43f18

Summary: [Folly] Cut extra `return` statement in `Core<T>::doCallback`.

Reviewed By: Orvid

Differential Revision: D15527963

fbshipit-source-id: 9396f9ac2b246676b33d13c87e24dd42198a11ec

Summary:
[Folly] Template fibers baton timed-wait over the deadline types, rather than over the timeout types and rather than fixing a single timeout type.

Templating it over the deadline types permits specifying the clock and permits passing a single deadline through unchanged through multiple time-delayed layers of code without skew, and templating it rather than fixing it over a single timeout type permits caller-specified fine-grained or coarse-grained timings.

Currently, the `EventBase` timers do not parameterize over the deadline types, so the fiber version of timed-wait must for now convert to a fixed timeout type.

Reviewed By: andriigrynenko

Differential Revision: D15448177

fbshipit-source-id: aa3fdbffdcb83cbfd1571780ba431a1004beb347

Summary: it seems since D15286181, we updated docker os_image to ubuntu18 and gcc7. this diff changes the README.md to reflect the change.

Reviewed By: yfeldblum

Differential Revision: D15513580

fbshipit-source-id: 0a3518c21c912903921946850bd08c948f09c295

Summary:
[Folly] Disable TLS optimization in PIC mode for `SingletonThreadLocal`.

In PIC mode, TLS offsets must be translated to addresses at runtime via calls to `__tls_get_addr`. Since there is not much of a small inline path or a fast inline fast path anymore anyway in PIC mode, might as well skip the bulky slow caching.

Also, some versions of gcc do not properly support this code in shared libraries. Details in #1135 and https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90562.

Fixes #1135.

Reviewed By: andriigrynenko

Differential Revision: D15468086

fbshipit-source-id: 038e13f900fe56205c1333a620ea3bfa468c47ad

Summary:
Avoid redefinition of mmsghdr with newer Android NDK unified headers.

Unified headers unconditionally define `struct mmsghdr`, but the `sendmmsg` and `recvmmsg` system calls are conditional on API level. API 21 is the first level that supports them.

Reviewed By: yfeldblum

Differential Revision: D15344307

fbshipit-source-id: 6f03197cc346511ce7a02f1468c35313140a8fd7

Summary:
The `TIMESTAMP_TX` flag can be used to signal a request TX / NIC timestamping. This flag needs to be passed through to the application via the `SendMsgParamsCallback::getAncillaryData` callback so that the application can populate a socket control message with the ancillary data required to signal the timestamping request.

`folly::AsyncSSLSocket` has extra logic for tracking the end of record (EOR) byte, but this logic currently only passes through `WriteFlags::EOR`. This diff adds support for passing through any flag specified as an EOR-related write flag when the EOR byte is written. As part of this change, the relevant unit tests are extended / cleaned up (some of them still reference MSG_EOR, which is out of date).

Reviewed By: yfeldblum

Differential Revision: D15465432

fbshipit-source-id: 2ab5619607959dd829427a695aefd95a33b4abce

Summary: Need to use `readAll` to ensure that we've read in all bytes that were written (up to EOF). Current approach sometimes returns after only a partial read.

Reviewed By: yfeldblum

Differential Revision: D15456484

fbshipit-source-id: f36a596a3557d4d3714bfaa3c33c726d81ccb5a4