Summary:
Part of the added comment about `folly::coro::merge()`:

  // Currently this doesn't fully do structured concurrency. Care is needed to
  // avoid use-after-free when the stream is terminated early, as some cancelled
  // input streams may be left running in background.
  // The rule is: if output generator's next() returned an empty value
  // (end of stream), it's guaranteed that 'sources' and all input coroutines are
  // completed and destroyed, no use-after-free danger. In all other cases
  // (next() returned an exception or the output generator was destroyed early),
  // the input generators may be left running in background (cancelled and
  // detached).

This diff adds a long comment about this and a couple other quirks (or what I would consider quirks).

It also fixes one of the quirks: the merged stream may return end-of-stream when 'source' coroutine frame is not destroyed yet. So if the 'source' coroutine e.g. has a `SCOPE_EXIT` that references some state owned by the caller of `merge()`, it may in principle use-after-free. This diff destroys 'source' coroutine frame just before returning end-of-stream rather than just after. This way `merge()` is at least possible to use in "strucutured concurrency" style, as long as you avoid exceptions and always drain the merged generator before destroying it.

It would be easy to do the same for the exception case (just wait for the `makeConsumerTask()` coroutine to complete before calling `throw_exception()`). This would make `merge()` as close to structured concurrency as is possible with `folly::AsyncGenerator` (which can always be synchronously destroyed, leaving no choice but to detach child coroutines; but as long as the user doesn't do that, it should be fine). But I'm hesitant to do it because some existing call sites might rely on current behavior. I'll leave this to the team that actually owns this code. Same for the two cancellation quirks listed in the added comment.

Reviewed By: iahs

Differential Revision: D33557074

fbshipit-source-id: cf7aaee8ec78e21c370d1f7faff3b4bad1327c95

Summary:
folly::fibers uses a SIGSEGV handler to detect fiber overflows, by checking if
the faulting address resides within a guard page range.

In the case when it does not, prior to this diff, the folly::fibers signal
handler would reraise the signal and allow the previous sigsegv handler handle
the exception.

The problem with this is that reraising the signal will discard the original
`siginfo` context sent by the kernel. The old signal handler would lose
visibility on the machine state, faulting condition, etc.

This does not play nicely with folly::symbolizer. Typically,
folly::symbolizer's signal handler will print information on the faulting
signal, such as:

```
*** Signal 11 (SIGSEGV) (0xdeadbeef) received by PID 3140647 (pthread TID 0x7fe2cddf1380) (linux TID 3140647) (code: address not mapped to object), stack trace: ***
    @ 00000000002f4d3d folly::symbolizer::(anonymous namespace)::signalHandler(int, siginfo_t*, void*)
                       ./folly/experimental/symbolizer/SignalHandler.cpp:449
    @ 0000000000000000 (unknown)
    @ 00000000002dd0f9 doCrashWildRead()
                       ./scripts/mingtao/oneoffs/crash.cc:9
    @ 00000000002dd0b1 main
                       ./scripts/mingtao/oneoffs/crash.cc:47
    @ 0000000000025dc4 __libc_start_main
    @ 00000000002dcfb9 _start
                       /home/engshare/third-party2/glibc/2.30/src/glibc-2.30/csu/../sysdeps/x86_64/start.S:120
Segmentation fault (core dumped)
```

From the error message, you can see that:
* the faulting address was 0xdeadbeef
* the reason for SIGSEGV was because the application accessed a region of memory outside of its virtual address space

If you happened to have used `folly::fibers` somewhere within your application, though, you instead would see this:

```
*** Aborted at 1639532805 (Unix time, try 'date -d 1639532805') ***
*** Signal 11 (SIGSEGV) (0x1c85b0032a0f8) received by PID 3318008 (pthread TID 0x7f5573e8d380) (linux TID 3318008) (maybe from PID 3318008, UID 116827) (code: -6), stack trace: ***
    @ 00000000002f4e0d folly::symbolizer::(anonymous namespace)::signalHandler(int, siginfo_t*, void*)
                       ./folly/experimental/symbolizer/SignalHandler.cpp:449
    @ 0000000000000000 (unknown)
    @ 00000000002dd169 doCrashWildRead()
                       ./scripts/mingtao/oneoffs/crash.cc:9
    @ 00000000002dd124 main
                       ./scripts/mingtao/oneoffs/crash.cc:48
    @ 0000000000025dc4 __libc_start_main
    @ 00000000002dcfb9 _start
                       /home/engshare/third-party2/glibc/2.30/src/glibc-2.30/csu/../sysdeps/x86_64/start.S:120
```

`code: -6` corresponds to `SI_TKILL`, indicating that the signal was a result of some process invoking `tgkill` (this is the fiber handler re-raising the signal)

And `0x1c85b0032a0f8` is some bogus value, since signals raised by `tgkill` do not have a valid si_addr field.

Furthermore, when debugging the core file, `p $_siginfo` will no longer give the relevant machine state at the time of the crash, since `$_siginfo` now would correspond to the
raised signal by folly::fibers, rather than the original fault.

This diff changes the `raise` to a synchronous invocation of the old signal handler. This allows the original signal context to be properly preserved (and visible within core).

Reviewed By: Gownta

Differential Revision: D33165801

fbshipit-source-id: 4526d5a9a93cf1eba13e9f5a16b13d00b3c8c85b

Summary: Add variadic template argument parameters to async_invocable_inner_type (so it can support overloaded callables).

Differential Revision: D33534807

fbshipit-source-id: 8bd1d2bc48bb27592b9d728dbd67e85bbed32144

Summary: I don't see how this header works, as it includes folly/Portable.h (which defines FOLLY_HAS_STRING_VIEW) _after_ it has already used FOLLY_HAS_STRING_VIEW a few lines up. Somehow, that worked with buck1 (really not sure how), but broke buck2.

Reviewed By: ot

Differential Revision: D33511408

fbshipit-source-id: 9e2da2a5c25a02367079254ff78552a5a335b3b1

Reviewed By: andriigrynenko

Differential Revision: D33532498

fbshipit-source-id: bd180566563576d003afced43684a8e0cb8e3cee

Summary:
folly::Subprocess attempts to close (nearly) all file descriptors if
`closeOtherFds()` option is set. When the process limit for number of
file descriptors is large, but the actual number of open descriptors is low,
much time is spent calling `close()` on files that are not actually open.

On Linux, we can use the information in `/proc/self/fd` to close only those
files that are actually open to speed up the process in the normal case.

Reviewed By: yfeldblum

Differential Revision: D33128499

fbshipit-source-id: efa5a348ff657c8212d9329a3efc7dd5bc0bb4d9

Summary: This ensures that when we collect the normal stack traces while collecting the async stack traces, the normal stack addresses are within a valid range. The normal stack addresses may be invalid because some functions may not follow the usual calling convention, for example with TSAN or with Lua FFI calling into C++.

Reviewed By: yfeldblum

Differential Revision: D32108552

fbshipit-source-id: 97b652f5e71b67dfa810549d837c7a0393d7c4cb

Summary:
Fixes the bug referenced in the base commit of this stack.

Given that `folly::dynamic(1) == folly::dynamic(1.0)` returns true, `folly::dynamic(1) < folly::dynamic(1.0)` should return false to maintain ordering properties.

Regarding the PrintTo test change - the keys in the json map are ordered - so now the numeric ordering behavior kicks in and order is changed. If we really wanted to we could use a custom comparator for when `json::serialization_opts::sort_keys == true` but this option I'm guessing is only for easing human consumption, and json keys of float-like things are probably not common so complicating the code may not be warranted.

Reviewed By: Gownta

Differential Revision: D33465565

fbshipit-source-id: 21859a1b0e63cc8c3d0c002f3478baae1cf7fc18

Summary:
Fixes the bug referenced in the base commit of this stack.

Given that `folly::dynamic(nullptr) == folly::dynamic(nullptr)` returns true, `folly::dynamic(nullptr) < folly::dynamic(nullptr)` should return false to maintain ordering properties.

Reviewed By: Gownta

Differential Revision: D33456202

fbshipit-source-id: 3fc994cd76d6e119884e017f68b445ed438f7cea

Add tests for folly::dynamic ordering comparison operators on scalar/string types and highlight some bugs

Summary:
# Summary
Currently nullptr vs nullptr and int vs double ordering comparison operators (e.g. `operator<`) are inconsistent with their equality operators.

This diff just adds tests to increase coverage and highlight the broken areas. The subsequent diffs will address the issues individually.

The behavior on nulls at least has been present since the very beginning of when a CompareOp was added for it in 2017.

More details are below.

# Bug 1: nullptr vs nullptr
If we have
```
folly::dynamic a(nullptr);
folly::dynamic b(nullptr);

a < b // returns true
a == b // returns true
```
This violates that the two should be equal if `!(a < b) && !(b < a)` given that this expression will return `false`, whereas `a == b` returns `true`.

This property is required by e.g. std::sets.
If one puts a `folly::dynamic(nullptr)` in an std::set with the current behavior, when iterating it will be found, and will contribute to its size, but `std::set::find()` on it will return false. Hash-based sets are unaffected - given that the hash and `operator==` implementations are correct.

The fix is straightforward.
`struct dynamic::CompareOp<std::nullptr_t>` in dynamic-inl.h should return false.

# Bug  2: int vs double (hash + ordering operators)
The `folly::dynamic==` operator does numeric comparison for int64 vs double - whereas the `folly::dynamic<` operator does not - instead falling back on comparing against the Type enum value. Similar to the above this violates the principle of `operator<` being usable for checking equality - given that it is really just checking type equality - but has already been established in the code path that they're different types.

Hashing is also inconsistent given that a hash of dynamic(2.0) will not equal dynamic(2) even though they are equal, given that each uses the hash of the underlying type. When ordering is fixed, hashing should be too so that hash based and ordering based containers have the same behavior.

The fixes are straightforward.

operator< in dynamic.cpp should pull the same logic from operator== with regards int vs double.
See https://www.internalfb.com/code/fbsource/[4e70ca24b9ec]/fbcode/folly/dynamic.cpp?lines=97-126

hashing can be resolved by having doubles use integer hashing in dynamic.cpp - https://www.internalfb.com/code/fbsource/[4e70ca24b9ec]/fbcode/folly/dynamic.cpp?lines=307

 ---

Reviewed By: Gownta

Differential Revision: D33465564

fbshipit-source-id: 43b926837e20f4a9afe15ee0032d469864e360c0

Reviewed By: Gownta

Differential Revision: D33476592

fbshipit-source-id: 9e66fdf07ce88c507cfb32406b113e1c05131c8c

Summary: This opportunity was found with the combination of Infer's PULSE_UNNECESSARY_COPY and Strobelight cycle counts.

Reviewed By: Gownta

Differential Revision: D33304127

fbshipit-source-id: 7d3b54d26bc3e171cc7a0a831933fdbb9638f6a8

Summary: sizeof(SharedMutex) = 4, sizeof(std::mutex) = 40. This diff makes sure that we use smaller mutexes both in Observer Core and in Observables given that we may end up with many instances of these objects, yet there mutexes are accessed only on the update path.

Reviewed By: praihan

Differential Revision: D32271615

fbshipit-source-id: ba7d04632a677a9eb4ae398d681dadac3b06f033

Reviewed By: yfeldblum

Differential Revision: D33118848

fbshipit-source-id: c69b1f8f415b130d5d7a6487e7027d5c1e49865f

Summary: Add comments stating the expectations for Baton post and Futex wake native implementation to be async-signal-safe.

Reviewed By: ot, luciang

Differential Revision: D33461663

fbshipit-source-id: 2855427cc94f577b566b19203a4523f54a41d0aa

Summary:
A number of places were extracting dependencies from manifests, but only one was adding in the implicit dependencies for build tools.

Extract the logic to one place and use so that a change in a tool like cmake will now correctly affect all tools using cmake, as it will be taken into account as a dependency hash when the manifest's hash is computed.

Tests for this change revealed that install_dirs needed to be populated in reverse order from the manifest topo-sort, so have also addressed that

Reviewed By: wittgenst

Differential Revision: D32730717

fbshipit-source-id: 1b2a25e460de6085d274c99acfd391b3bd259264

Summary: We want to have a custom `IOExecutorThreadPool` that performs different logic for handling observers being adding or not. This change makes it so the functions and structs necessary to do so can be properly overriden.

Reviewed By: Gownta

Differential Revision: D32101852

fbshipit-source-id: 2f1c6bb4c00d41630891aa72b8e519708cb1a40f

Summary: When we build cmake on linux the openssl headers are needed

Reviewed By: fanzeyi

Differential Revision: D33432903

fbshipit-source-id: 2f869768f3a81b74e53391f5491781759c66b478

Summary:
If we already have pending application reads or writes when we have a
handshake error (eg when using a null connect callback), we should pass the
handshake error to finishFail to give a more helpful error message.

Reviewed By: mingtaoy

Differential Revision: D33415008

fbshipit-source-id: fc14ef774d09c0af975e177b24185f78c4e4139e

Summary: asm memset implementation based on the https://github.com/nadavrot/memset_benchmark implementation by Nadav Rotem

Reviewed By: luciang, magedm

Differential Revision: D32888087

fbshipit-source-id: 3678950ed5178d2a46ba833502d1a6aef4f2c731

Reviewed By: yfeldblum

Differential Revision: D32187345

fbshipit-source-id: d384aac90c5c0c10580824305ce108e7c0b0e577

Summary:
This avoids the following errors:

  folly/executors/ManualExecutor.h:42:3: error: '~ManualExecutor' overrides a destructor but is not marked 'override' [-Werror,-Wsuggest-destructor-override]

Reviewed By: r-barnes

Differential Revision: D33397861

fbshipit-source-id: f9bee89aeaa55d365155dc3fdc0b70b283980a2a

Summary:
This avoids the following errors:

  folly/io/async/ssl/OpenSSLTransportCertificate.h:31:11: error: '~OpenSSLTransportCertificate' overrides a destructor but is not marked 'override' [-Werror,-Wsuggest-destructor-override]

Reviewed By: r-barnes

Differential Revision: D33397487

fbshipit-source-id: 4237f5ad36166189b0bbd28dfcf268e0ef4b40f1

Summary:
This avoids the following errors:

  folly/experimental/coro/BlockingWait.h:301:3: error: '~BlockingWaitExecutor' overrides a destructor but is not marked 'override' [-Werror,-Wsuggest-destructor-override]

Reviewed By: r-barnes

Differential Revision: D33397860

fbshipit-source-id: 050c3c564e70dfc5dc1232e58b40f2c4cbcb660a

Summary:
This avoids the following errors:

  folly/io/async/ScopedEventBaseThread.h:49:3: error: '~ScopedEventBaseThread' overrides a destructor but is not marked 'override' [-Werror,-Wsuggest-destructor-override]

Reviewed By: ryanthomasjohnson

Differential Revision: D33397489

fbshipit-source-id: 29210c0de0b850bdda5d2c27a5be8971fc17b40e

Summary:
Update the README.md to reflect that getdeps.py build and test is the method tested in CI and thus preferred.

Where getdeps.py manifests encode dependencies I've removed the manually specified dependences from the README for consistency (e.g. googletest version in README was outdated, manifest is correct and is tested in CI)

Also referenced main vs master and improved markdown header formatting a little

Reviewed By: meyering

Differential Revision: D33295900

fbshipit-source-id: caec3b3795be0b37bf1efdf12f4dbf23a37a023c

Summary:
There is no current use case of this API throughout the codebase
and it's causing some confusions of how this class is used
so removing it for now. It's easy to add it back if we need it
in the future

Reviewed By: yfeldblum

Differential Revision: D33112001

fbshipit-source-id: c711f5ab0ad2324e478f6eb18155d367d2cce1f2

Summary: Looks like bad copy/pasta.

Differential Revision: D33279601

fbshipit-source-id: 24d3ad02422ac5af6a1624f09c719207ed4950a6

Reviewed By: aaronabramov

Differential Revision: D33358291

fbshipit-source-id: d22ff22b8c84ef7d60bafb41dd98acacea8f5ddb

Summary:
Adding methods to `folly::OpenSSLCertUtils` that allow to read extensions from X509 cert structures.
- `folly::OpenSSLCertUtils::getExtension()` allows to query extensions by name
- `folly::OpenSSLCertUtils::getAllExtensions()` returns everything including custom extensions.
No extension name translation mechanism is provided for custom extensions.

Reviewed By: mingtaoy

Differential Revision: D31852457

fbshipit-source-id: 22d34d2cf304ba135419c902d9c5c303f78cf781

Reviewed By: bhamodi

Differential Revision: D33330724

fbshipit-source-id: 8a798435742dedc96e2b6912179736b6a1c72491

Summary:
This test regularly times out under load.

I made a benchmark diff (prior to this in the stack, but not to be landed) which confirms (a) that the slowness of this test is due to spawning excessively-many threads, and (b) that the performance of ConcurrentSkipList doesn't unduly degrade with excessively-many threads. Conclusion: it is safe to simplify these tests.

To simplify the test, I ratcheted down the number of threads, but also bumped the number of iterations. Much more work is being done (so this test should retain its race-condition-hunting properties), but the time spent is much less, even when the system is under load.

Reviewed By: yfeldblum

Differential Revision: D33269899

fbshipit-source-id: 9f7a0ec5f3c1077c91e5d09c89f3752d552a6320

Summary: This test regularly fails on account of timing. Remove the timing upper bound.

Reviewed By: yfeldblum

Differential Revision: D33271470

fbshipit-source-id: 1369ef45bd49e500c35816bfdb21869f346b6f70

Summary: swap should be noexcept when possible

Reviewed By: yfeldblum

Differential Revision: D33198827

fbshipit-source-id: f8d52a21087b0346332359b66e1dc00f982ddbbb

Summary:
Externally this was failing on fedora 35's GCC 11.2.1

Add test so we know what platforms it's good on

Reviewed By: yfeldblum

Differential Revision: D33192636

fbshipit-source-id: 028255b6dbb34762b4e788122d948f26a449a57c

Summary: Try enabling this, need to handle linux ASM build case in cmake config

Reviewed By: Gownta

Differential Revision: D33191710

fbshipit-source-id: 6d49a08106c8a0044380f592fd2862080cbea454

Summary:
Having the tests is useful to be able to test the OSS builds. A few were failing for me locally so I've tagged them BROKEN in CMakeLists.txt which folly's cmake config filters out

Pull Request resolved: https://github.com/facebook/folly/pull/1691

Test Plan:
tested with:

```
./build/fbcode_builder/getdeps.py --allow-system-packages build
./build/fbcode_builder/getdeps.py --allow-system-packages test
...
100% tests passed, 0 tests failed out of 2736

Total Test time (real) =  14.95 sec
````

Reviewed By: yfeldblum, Gownta

Differential Revision: D33169409

Pulled By: ahornby

fbshipit-source-id: 9c781a84b8873c295af96368dd8315254a78f096

Summary:
Ensure that folly continues to work with platform010. Since folly is depended on my many projects, some on platform009 and some on platform010, we should make sure it continues to work with both platforms.

Since many platform010 projects depend on folly, folly's platform010 coverage is actually pretty good. However, changes to test files in folly have been observed to break with 010-incompatible changes (such as D33143441 (https://github.com/facebook/folly/commit/43ba86e231ab5cb158835433df656d3026c3c6cf) and D32930335 (https://github.com/facebook/folly/commit/cec3fcac4dded35478747e4d9b8e533b491140e1)); these are not caught by dependent projects' configs.

Reviewed By: yfeldblum, meyering

Differential Revision: D33172025

fbshipit-source-id: 94b46471bee604289b3b6a11763a27c6e3ed9fcf

Summary: sosorry

Differential Revision: D33218659

fbshipit-source-id: e7c77b503ef6c7144fd8da684b22f793d85b2b96

Summary: `ResultOf` is no longer the most-suitable name. This helper has long been a SFINAE helper and its actual output did not matter, but now that it is always `void` the name is even less clear. Rename it.

Reviewed By: luciang

Differential Revision: D33155200

fbshipit-source-id: a12842c6be38bd82bfffa85193ec265bc4d803ad