make IOBuf::coalesce return ByteRange

Test Plan: fbconfig -r folly/io && fbmake opt -j32 && fbmake runtests_opt

@override-unit-failures

Reviewed By: soren@fb.com

FB internal diff: D1005735
Migrating folly to gcc-4.7.1

Summary:
folly/PLATFORM is the last fbcode platform on gcc-4.6.2.

Before pushing, I ran arc unit from my devserver (see Test Plan).
Phabricator's test run has a lot of aborted test cases, which are
indicative of a failing test framework. Arc unit had been
intermittently broken when running my own tests. Overriding
Phabricator's unit test failures:
@override-unit-failures

Test Plan:
(1) fbconfig -r folly/ -- build and runtsts in dbg and opt.

Everything is passing.

(2) arc unit, look at each failed result

Some builds/tests are failing. Most seem unrelated. Of the rest, one is
also failing on master, and the others did not fail during a second run.

Reviewed By: andrei.alexandrescu@fb.com

FB internal diff: D1005889
Use Mach built-ins in lieu of clock_gettime(3) and friends.

Summary:
- Mach doesn't support clock_getres(3) or clock_gettime(3). Provide our
own implementations by wrapping mach_timebase_info() and
mach_absolute_time().
- Detect availability of of -lrt at configure time and don't link with
it if it's not available. On Linux, this is what provides
clock_gettime(3) and friends.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: meyering@fb.com

FB internal diff: D999131
Detect libc++ in configure.ac.

Summary:
- Explicitly detect use of libc++ in configure.ac and reflect this in
folly-config.h. Do this rather than looking for to pop up organically
_LIBCPP_VERSION since this only exists if we've included some libc++
header files prior to refernce. This isn't always the case, e.g. in
Portability.h.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: simpkins@fb.com

FB internal diff: D1002958
Check for std::this_thread::sleep_for.

Summary:
- Some installations of libstdc++ don't have this defined. This happens
if they were built without --enable-libstdcxx-time. Detect this and
avoid tests that rely on this behavior.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: meyering@fb.com

FB internal diff: D1002963
Detect C++ implementations that support constexpr strlen()

Summary:
- Only declare the Range constructor as a constexpr if strlen() is also
a constexpr. Otherwise, we'll get compilation errors.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: soren@fb.com

FB internal diff: D1003124
Set -std=XXX flags earlier; use in AC_COMPILE_IFELSE()

Summary:
- We had a bug where AC_COMPILE_IFELSE() invocations weren't using the
same -std=XXX flags that we're using in our actual build. This
happened because we made these checks before figuring out which
flag to use.
- Stop setting -std=XXX flags in CPPFLAGS. It's only useful for
CFLAGS/CXXFLAGS.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: meyering@fb.com

FB internal diff: D1003972
Only run FBString.testConstructionFromLiteralZero under GNU libstdc++

Summary:
- This test verifies the behavior of std::string(0), which the GNU
library expects to throw an std::logic_error. Other libraries may have
other behaviors; libc++ segfaults.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: simpkins@fb.com

FB internal diff: D1003125
Detect and use std::is_trivially_copyable<T> where possible.

Summary:
- Sadly, boost::has_trivial_copy<T> is not a suitable replacement for
std::is_trivially_copyable<T> on libc++. Fortunately, the latter is
actually supported (and works), so use it directly.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: delong.j@fb.com

FB internal diff: D1008921
Remove check that depends on malloc implementation.

Summary:
- The EXPECT_EQ(vec.capacity(), vec2.capacity()) check is implicitly
testing how the platform's malloc() and malloc_usable_size()
implementations interact. We know that small_vector will attempt to
allocate storage for 3 elements via malloc(), but the small_vector
implementation then uses malloc_usable_size() to determine capacity,
which can return more than the size requested by malloc(). As a
result, capacity may grow more than expected depending on how the
malloc implementation works.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: alandau@fb.com

FB internal diff: D1008922
Remove trailing comma in configure.ac.

Summary:
- We were inadvertantly emitting a superfluous comma when generating the
configure script, causing it warn on execution. This was caused by
separating two AC_DEFINE() invocations w/ a comma.

Test Plan:
- fbconfig -r folly && fbmake runtests
- ./configure && make check on Ubuntu/FC/Mac

Reviewed By: meyering@fb.com

FB internal diff: D1008924
Include cpp only when needed

Summary:
D1008921 broke compilation for tao which uses folly/Portability.h
This diff guards the change for only c++ code. Not sure if this breaks the
definition of portability.

Test Plan: Compile tao, fbconfig -r folly and fbmake runtests

Reviewed By: simpkins@fb.com

FB internal diff: D1010967

@override-unit-failures
folly, tao: don't impose C constraints on folly's Portability.h

Summary:
* folly/Portability.h: Move the definitions that Tao uses
into a new file, and include that new file here.
* folly/AddressSanitizer.h: New file.
* tao/server/config.h: Include that small new file, rather
than all of folly's Portability.h

Test Plan:
fbconfig -r tao/server &&
tao/server/tests/run_unit_tests.sh -d --save-log=log
For folly, watch the arc-run tests.

Reviewed By: pgriess@fb.com

FB internal diff: D1011800

@override-unit-failures
fix a few bugs in FBString

Summary:
* `push_back()` fails for medium strings of zero capacity if not linked
with jemalloc (see added test),
* we incorrectly initiliaze capacity when acquire mallocated string
(forgot about null terminator).

Test Plan: fbconfig --allocator=malloc folly/test:fbstring_test_using_jemalloc && fbmake runtests_opt

@override-unit-failures

Reviewed By: tudorb@fb.com

FB internal diff: D1012196
Change FBString's #define throw

Summary:
Instead of defining throw to nothing, define it to something
which creates a grepable error message (re @tudorb in D1005889).

@override-unit-failures

Test Plan:
fbconfig -r folly
fbmake dbg && fbmake runtests && fbmake opt && fbmake runtests_opt

All tests passing.

Added throw to a few places in FBString; noticed that error messages
were produced, and that they contained the defined text. Those changes
not committed.

Reviewed By: tudorb@fb.com

FB internal diff: D1011963
Issue with find and npos

Summary:
I dont know whats the expected behavior but for std::string it seems
to work.

@override-unit-failures

Test Plan:
unit-tests

[ RUN      ] FBString.findWithNpos
folly/test/FBStringTest.cpp:1147: Failure
Value of: fbstr.find(":", fbstring::npos)
Actual: 9
Expected: fbstring::npos
Which is: 18446744073709551615

Reviewed By: andrei.alexandrescu@fb.com

FB internal diff: D1012870
avoid using ifunc + ASan

Summary:
Code that is using ifunc dies with SIGSEGV on startup when used
with ASan.

Here is gdb output: {P2882504}

Seems like `ifunc` dispatch is happening before ASan is initialized,
but ASan instrumentation logic being called from there.

Test Plan:
built affected unicorn binaries with ASan, ran them, verified
there is no more SIGSEGV

Reviewed By: meyering@fb.com

FB internal diff: D1013420
exponential capacity growth for io::TypedIOBuf

Summary:
Amortized cost of `TypedIOBuf::push()` is `O(N)` at this moment.
Unless we're using jemalloc where we can rely on `realloc()`.  In this
diff we switch to exponential growth otherwise.

Test Plan:
built unicorn/test with ASan (and thus without jemalloc), ran
end-to-end tests and verified we no longer spend minutes to build di4

@override-unit-failures

Reviewed By: tudorb@fb.com

FB internal diff: D1015233
fix typo in comment

Summary: Pretty sure it was meant to be this way...

@override-unit-failures

Test Plan: n/a

Reviewed By: tudorb@fb.com

FB internal diff: D1020789
Add missing include

Summary:
MemoryMapping.cpp uses DEFINE_int64() from gflags,
but doesn't include it anywhere.

@override-unit-failures

Test Plan: OSS build failure goes away

Reviewed By: seanc@fb.com

FB internal diff: D1026364