Summary:
Using _r_debug offers a number of benefits:
- It allows us to symbolize addresses in data segments like .bss that
  are marked "[heap]" in /proc/<pid>/maps.
- It requires a lot less code.

It also fixes a preexisting bug where we would fail to symbolize
addresses that fell in any section past the first in any position-
independent objects.  Since `elfFile->getBaseAddress()` should always
return 0 for any PIEs, we wouldn't correctly adjust the address to be
ELF-relative when performing symbol lookup.  (For the first section,
we just used the start of the range we found in /perf/<pid>/maps.)

There is a minor downside:
- We have to open an ELF header for each object in order to check if a
  given address is in the range of some segment.  Before, we used
  /proc/<pid>/maps to make the range check, and only opened the header
  once we knew it was the one we wanted.  In the common case, however,
  where the addresses are from our own executable, we don't open any
  more files than before (and, in fact, one fewer).

Reviewed By: luciang

Differential Revision: D3695872

fbshipit-source-id: 9bdcc77da4d658ffad5c671f9b8ea65a471ed64f

Summary:
[Folly] Remove `ConditionallyExistent`, because it violates the C++ spec.

The spec says that struct and class types occupy at least one byte. But the point of this class is to occupy zero bytes when the condition is false. That can't be made to work.

GCC and Clang support an extension allowing, in some cases, structs to occupy no space at all. But it violates the spec, and MSVC does not support the extension.

There is, sort of, the possibility of empty-base-class-optimization. But it will be very painful to use, and it will only work in some cases.

Since this is broken now, and fixing it would violate the C++ spec and break this under MSVC, it's better just to remove it.

Reviewed By: nbronson, Orvid

Differential Revision: D3696371

fbshipit-source-id: c475c6e15d9ff1bc4c44dc7e336ce74e6db640ef

Summary:
Instead of passing exactly one tuple of arguments to applyTuple,
this diff allows to pass any number (zero or more) of tuples.

This can be very handy when piecing together arguments for
a function call.

Reviewed By: yfeldblum

Differential Revision: D3681499

fbshipit-source-id: a75a448636759f71db8d303e9dccada5b559af54

__google_stl_debug_vector: erase() at invalid position: folly/experimental/test:future_dag_test - FutureDAGTest.RemoveNodeComplex

Summary:
```
[ RUN      ] FutureDAGTest.RemoveNodeComplex
terminate called after throwing an instance of 'std::out_of_range'
  what():  erase() at invalid position
*** Aborted at 1470867850 (Unix time, try 'date -d 1470867850') ***
*** Signal 6 (SIGABRT) (0x133c001ed107) received by PID 2019591 (pthread TID 0x7ff1e6df5980) (linux TID 2019591) (maybe from PID 2019591, UID 4924), stack trace: ***
    @ 00007ff1e702020f folly::symbolizer::(anonymous namespace)::innerSignalHandler(int, siginfo_t*, void*)
    @ 00007ff1e701faf1 folly::symbolizer::(anonymous namespace)::signalHandler(int, siginfo_t*, void*)
    @ 00007ff1e87c714f (unknown)
    @ 00007ff1e7cf6d02 gsignal
    @ 00007ff1e7cf8af5 abort
    @ 00007ff1e73880e4 __gnu_cxx::__verbose_terminate_handler()
    @ 00007ff1e7385ee5 __cxxabiv1::__terminate(void (*)())
    @ 00007ff1e7385f30 std::terminate()
    @ 00007ff1e73861c0 __cxa_throw
    @ 00007ff1e740ae00 std::__throw_out_of_range(char const*)
    @ 00000000004483db std::vector<folly::FutureDAG::Node, std::allocator<folly::FutureDAG::Node> >::_M_erase(__gnu_cxx::__normal_iterator<folly::FutureDAG::Node*, std::vector<folly::FutureDAG::Node, std::allocator<folly::FutureDAG::Node> > >)
    @ 00000000004478fa std::vector<folly::FutureDAG::Node, std::allocator<folly::FutureDAG::Node> >::erase(__gnu_cxx::__normal_iterator<folly::FutureDAG::Node const*, std::vector<folly::FutureDAG::Node, std::allocator<folly::FutureDAG::Node> > >)
    @ 000000000044770a folly::FutureDAG::remove(unsigned long)
    @ 0000000000424bc2 FutureDAGTest::remove(unsigned long)
    @ 000000000041f7ed FutureDAGTest_RemoveNodeComplex_Test::TestBody()
    @ 00007ff1e9b19361 void testing::internal::HandleExceptionsInMethodIfSupported<testing::Test, void>(testing::Test*, void (testing::Test::*)(), char const*)
                       /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest.cc:2420
                       -> /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest-all.cc
    @ 00007ff1e9b029de testing::Test::Run()
                       /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest.cc:2437
                       -> /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest-all.cc
    @ 00007ff1e9b02aca testing::TestInfo::Run()
                       /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest.cc:2612
                       -> /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest-all.cc
    @ 00007ff1e9b02cfc testing::TestCase::Run()
                       /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest.cc:2730
                       -> /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest-all.cc
    @ 00007ff1e9b0d2a7 testing::internal::UnitTestImpl::RunAllTests()
                       /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest.cc:4602
                       -> /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest-all.cc
    @ 00007ff1e9b0d60c testing::UnitTest::Run()
                       /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest.cc:2420
                       -> /home/engshare/third-party2/gtest/1.7.0/src/gtest-1.7.0/src/gtest-all.cc
    @ 00007ff1eb64ec70 RUN_ALL_TESTS()
    @ 00007ff1eb64ec3c main
    @ 00007ff1e7ce10f5 __libc_start_main
    @ 000000000041f2d2 (unknown)
Summary (total time 0.07s):
  PASS: 0
  FAIL: 0
  SKIP: 0
  FATAL: 1
    folly/experimental/test:future_dag_test - FutureDAGTest.RemoveNodeComplex
  TIMEOUT: 0
````

Reviewed By: yfeldblum

Differential Revision: D3700956

fbshipit-source-id: dffca9460ccca1d8069218c5b7310e4d6e061697

Summary:
Implements a polymorphic functor for FutureDAGs. In order for FutureDAGs to be stateful they must be wrapped by a class of some sort. This is a really common pattern which we've been using in Gossit (and further - across the RedWood stack) in order to maintain state, and we feel it's generalized enough to be useful elsewhere.

`state` is an instance of the type declared in the template, and the exec* methods wrap go().get() so client-side implementations only have to touch the functor after construction in order to drive their DAGs.

Reviewed By: tjkswaine

Differential Revision: D3685651

fbshipit-source-id: 81169aefcff13ac8cc6cbb6bef6d90047732ad8a

Summary: Gate `kIsLinux` to not include `FOLLY_MOBILE` because "mobile" linux does not really behave like real linux.

Differential Revision: D3697717

fbshipit-source-id: 1b0f4208d2f71c35399c30f20a71bfa4ba4724e8

Summary:
Noticed this while debugging other timerwheel changes.  Scheduling new events in callbacks may result in us *running them right away* if they land in a bucket we are currently processing.

Instead, round up all the timeouts, then run them separately.  This means you can never schedule a timeout that will run immediately (0ticks), but that's probably fine.

Reviewed By: yfeldblum

Differential Revision: D3679413

fbshipit-source-id: 7e18632f23ea33c072c2718e30b378641895b094

Summary:
Standard (21.4.7.2 / 1):

> Determines the lowest position xpos, if possible, such that both of the following conditions obtain:
- pos <= xpos and xpos + str.size() <= size();
- traits::eq(at(xpos+I), str.at(I)) for all elements I of the string controlled
by str.

The existing logic violates the first requirement for `str.size() == 0` by
unconditionally returning `pos`.

Reviewed By: ot, Gownta

Differential Revision: D3698862

fbshipit-source-id: 9622f1b99b259d2d81ae83795dff9cd94619c725

Summary: Because, if no inlining is enabled, the absence of this attribute caused compile errors due to functions that were expected to return a value not returning a value.

Reviewed By: meyering

Differential Revision: D3698413

fbshipit-source-id: 8f3505b17a2fa7b9710e3fb56d18c6ca00feacb3

Summary: With WinSock, calling `getsockname` on a socket before it's been bound will always result in an error, so make sure to bind the socket first.

Reviewed By: yfeldblum

Differential Revision: D3698112

fbshipit-source-id: e9efe05323b242add3808ee1a6fec2593beb04ac

Summary: `/dev/null` doesn't exist on Windows, but thankfully, `NUL` does, and has the same semantics.

Reviewed By: meyering

Differential Revision: D3698007

fbshipit-source-id: 5ef31c6576f988dd747ea3c39e296c244bc640b7

Reviewed By: yfeldblum

Differential Revision: D3691541

fbshipit-source-id: 9488c1487ebd0500a23300292215456ca3220f03

Summary:
Deleter helper object, which may release multiple ReadMostlyMainPtrs at once.
This allows underlying ref count implementation to perform expensive synchronization operations (e.g. asymmetric heavy barrier only once).

Reviewed By: yfeldblum

Differential Revision: D3691524

fbshipit-source-id: 3ac593b0d813345daba3a81ff4e2eb71b4db292e

Summary:
If one of the assertions failed, it would result in any threads that are still running accessing already-disposed data, so wait for the threads to exit, even when an exception is thrown.

This also slightly cleans up the handling of threads a bit further down, because the mess it was doing was completely unnecessary.

Reviewed By: yfeldblum

Differential Revision: D3692438

fbshipit-source-id: 9082ba248b2cf1062e46c97faf0bc062312ee9ae

Summary:
See the comment on `msvcReturnInvalidParams` for more info on the issue.
This also adds a use of it to TestUtilTest.

Reviewed By: yfeldblum

Differential Revision: D3691526

fbshipit-source-id: f0f596e9b4c830e1d31de01926162636757329e8

Summary: Also switch `pipe` to return a socket pair instead, as libevent can't poll against a pipe on Windows. And lastly, fix the file descriptor for sockets leaking when close is called.

Reviewed By: yfeldblum

Differential Revision: D3691255

fbshipit-source-id: c684242d255ac5158a4c805d432d345dac1b3bd8

Summary: Pah! This definitely wasn't causing the lock tests to segfault. Nope, not at all <_>.

Reviewed By: yfeldblum

Differential Revision: D3691120

fbshipit-source-id: 6601db637f22c7b0bc326907a2a7976f6df7c159

Summary:
Also handle invalid file descriptors correctly and switch away from `WSASendMsg` for the implementation of `sendmsg` due to limitations imposed by WinSock.
This also fixes up a few places that were explicitly referencing the global version of some socket functions, which was bypassing the socket portability layer.

Reviewed By: yfeldblum

Differential Revision: D3692358

fbshipit-source-id: 05f394dcc9bac0591df7581345071ba2501b7695

Summary: Just calling `SetEnvironmentVariableA` wasn't updating `_environ`, which meant that calls to `getenv` weren't reflecting the changes made via `setenv`. The correct way to implement it is using `_putenv_s`, but there's one problem with that: passing an empty string as the value to `_putenv_s` results in the environment variable being unset. To make it possible to set the environment variable to an empty string, we shall dive head-first into the implementation details of the CRT and emerge victorious by blatently ignoring the documentation of `getenv` and modifying the string it returns to terminate it early.

Reviewed By: yfeldblum

Differential Revision: D3691007

fbshipit-source-id: 350c2ec72ec90b9178a9a45b2c2ed2659b788e37

Summary: Windows is weird and calls it USERNAME instead, so just use one that everything agrees on: PATH

Reviewed By: yfeldblum

Differential Revision: D3691072

fbshipit-source-id: 579c6484736ef47e130049c29bef8b59c66a4482

Summary: Because the comment was a lie; sockets are blocking by default, not non-blocking.

Reviewed By: yfeldblum

Differential Revision: D3691145

fbshipit-source-id: 5d3c62b3573205fe416d77fe4b5b9fbd593ffd93

Summary:
The getTFOsucceeded doesn't really work right now
as intended. Currently we check right after sendmsg,
however we can only know whether or not the server
has acked the data after 1-RTT.

This removes getTFOSucceeded. Will fix in another diff.

Differential Revision: D3679235

fbshipit-source-id: 6b2bb01d3743ea7e68ad3cc9a26be6806f17ffbe

Summary:
[Folly] `constexpr_abs`.

Is `constexpr`.

Works over integral and floating types.

If given an integral type, the return type is the usigned version of that integral type, thereby avoiding the undefined behavior of `std::abs(std::numeric_limits<int>::min())`.

Reviewed By: simpkins

Differential Revision: D3654072

fbshipit-source-id: 24fefc0c3b055f78ba3e07472c38fb9c550e0f31

Removing noexcept specifications in constructors for Synchronized that call contextualLock() and contextualRLock()

Summary:
Most mutex lock() functions do not have a noexcept guarantee, saying that the
constructor for Synchronized based on whether the underlying constructor for
the type stored is not enough.  Although this will *rarely* cause bugs, it
probably can be fixed

Reviewed By: simpkins

Differential Revision: D3682974

fbshipit-source-id: ec0bb701d0af41ffc79128fe8db7935a5f19bc70

Summary:
We are definitely not prepared to handle
SIGPIPEs, so add MSG_NOSIGNAL to sendmsg
of AsyncSSLSocket.

This is a problem which exists in openssl
as well which calls send with flags = 0.
We recently made a change to move the send
into our control, so we can now supply the
flag

Reviewed By: yfeldblum

Differential Revision: D3686679

fbshipit-source-id: ff8fe662e62923c25876bdfd516352639505dca6

Summary:
Update the documentation for Synchronized to remove references to the
various SYNCHRONIZED macros, and document the lock() and withLock() APIs
instead.

Reviewed By: yfeldblum

Differential Revision: D3618871

fbshipit-source-id: e970f9a23e45831d62232eea2ba133a55e5a4a49

Summary: It calls syscall, but does not include the header.

Reviewed By: knekritz

Differential Revision: D3586636

fbshipit-source-id: 2ef05fc4b88f236a84b79afa708e98fe21529685

Summary:
Depends on D3648195

This test example is intended to demonstrate the methodology for using DeterministicSchedule support for auxiliary data and global invariants.
The main goal is fine-grained invariant checking, ideally after every shared update.
The secondary goals are:
- Minimize intrusion in the original code. In this proposed methodology, it is adding a friend.
- Minimize duplication of original tested code. Unfortunately, depending on the original code, it seems that significant duplication may be unavoidable if we don't want to change the original code.

This diff is primarily about the methodology for testing already developed code. I plan to apply what we agree on through this diff to the dynamic MPMCQueue code (D3462592).

A future goal to keep in mind is creating a methodology for developing new code with hooks for DSched aux. data and invariant checking integrated in it, in order to minimize or eliminate duplication of tested code.  In past projects, I used non-standard source code (basically algorithm code) that is automatically translatable through scripts and macros to input to a DSched-like tool as well as to compilable code. The main challenge for such a methodology is to allow the original source code to be standard readable C++ code.

Reviewed By: djwatson

Differential Revision: D3675447

fbshipit-source-id: aae2c9f0550af88dc3a5dcbe53318a75a86b6e2b

Summary: This switches the places in Folly that need to explicitly reference the socket portability implementation to do exactly that.

Reviewed By: yfeldblum

Differential Revision: D3299984

fbshipit-source-id: 57cd8ebe66c9055aba66581a8c0fcf6c125d96f9

Summary:
Add some tests to test the other levels of the timer wheel.

They are slow by necessity.

Reviewed By: yfeldblum

Differential Revision: D3637132

fbshipit-source-id: badf8d37d726dbeb5a8220d50c60b8efdaee7989

Summary: This feature doesn't make sense when wheeltimer doesn't constantly tick - we always have to get the current clock time.  On the plus side, we'll only be grabbing the clock on timer schedule or timeout, never for individual ticks.

Reviewed By: yfeldblum

Differential Revision: D3637088

fbshipit-source-id: ed8fe52419259332a14b6dc1d357979dcf258a20

Summary: It's perfectly possible that the default crypto context simply hasn't been created yet, so try to create it if the initial acquisition fails.

Reviewed By: yfeldblum

Differential Revision: D3673138

fbshipit-source-id: 122955df04055ff4f99513b182375d4388dd0305

Summary: As-of C++11, destructors are assumed to be `noexcept` unless explicitly marked otherwise. `Watchdog`'s destructor throws, so switch it to a `LOG(FATAL)` instead.

Reviewed By: andriigrynenko

Differential Revision: D3672621

fbshipit-source-id: 5224ecf85d101462e02e12da257e033bab4db1a1

Adding policies for all the upgrade and downgrade mutex transitions that are going to be supported by Synchronized

Summary:
This diff contains the lock policies that will be used by Synchronized to
implement mutex transitions by means of heterogenous RAII mutex wrappers

Reviewed By: yfeldblum

Differential Revision: D3665020

fbshipit-source-id: a5509dfd58a1dd6cd60a7d3afe929d0da860926d

Summary:
This diff adds support for upgradable mutexes to the LockTraits
abstraction used by folly::Synchronized

Reviewed By: yfeldblum

Differential Revision: D3645453

fbshipit-source-id: 30f16eb3fbebc687a4136256f1103962c0e4c465

Summary: Because the former is standardized, and the latter is a syntax error under MSVC.

Reviewed By: yfeldblum

Differential Revision: D3672667

fbshipit-source-id: c0149b11367e36ba5574625240c41a167348199f

Summary: RequestContext update.

Reviewed By: mibpl

Differential Revision: D3604937

fbshipit-source-id: 07b315fe22a6dba40f0bab53c8092f35c172ae85

Summary: The portability implementation of `mmap` for Windows doesn't currently support anonymous shared allocations, as they are non-trivial to manage, and the places this is being used doesn't actually need the memory to be allocated as shared, so allocate it as private instead.

Reviewed By: yfeldblum

Differential Revision: D3671495

fbshipit-source-id: e74d4fd925363fef16c1bf8445da1ff32bf8266d

Summary: The tests aren't dependent on it being pthread, so use standardized stuff instead.

Reviewed By: yfeldblum

Differential Revision: D3665698

fbshipit-source-id: ad91facb75a9c5d7a90bfa294cc98bb07629de1b

Summary: Without `WIN32_LEAN_AND_MEAN` defined, including `Windows.h` includes a massive number of extra headers. There are situations that need things that are defined in those headers, so keep folly working even when it isn't defined.

Reviewed By: yfeldblum

Differential Revision: D3671350

fbshipit-source-id: 0de986e17cdd4be386be8a9eeb0075b4af44024d