Enable pcntl for CLI containers

[renatomefi]

When on a orchestration environment it's really common to containers to receive signals from it, this makes pcntl essential to live within those platforms and allowing developers to gracefully handle those signals.

[yosifkit]

Currently, we only enable extensions that cannot be enabled after the fact (like #439, #236 and #195). Like many extensions, this one can easily be added with docker-php-ext-install.

$ docker run -it --rm php:cli bash
root@fb9df8acc0c9:/# docker-php-ext-install pcntl
Configuring for:
PHP Api Version:         20170718
Zend Module Api No:      20170718
Zend Extension Api No:   320170718
checking for grep that handles long lines and -e... /bin/grep
checking for egrep... /bin/grep -E
checking for a sed that does not truncate output... /bin/sed
checking for cc... cc
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... no
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether cc accepts -g... yes
checking for cc option to accept ISO C89... none needed
checking how to run the C preprocessor... cc -E
checking for icc... no
checking for suncc... no
checking whether cc understands -c and -o together... yes
checking for system library directory... lib
checking if compiler supports -R... no
checking if compiler supports -Wl,-rpath,... yes
checking build system type... x86_64-pc-linux-gnu
checking host system type... x86_64-pc-linux-gnu
checking target system type... x86_64-pc-linux-gnu
checking for PHP prefix... /usr/local
checking for PHP includes... -I/usr/local/include/php -I/usr/local/include/php/main -I/usr/local/include/php/TSRM -I/usr/local/include/php/Zend -I/usr/local/include/php/ext -I/usr/local/include/php/ext/date/lib
checking for PHP extension directory... /usr/local/lib/php/extensions/no-debug-non-zts-20170718
checking for PHP installed headers prefix... /usr/local/include/php
checking if debug is enabled... no
checking if zts is enabled... no
checking for re2c... re2c
checking for re2c version... 0.16 (ok)
checking for gawk... no
checking for nawk... nawk
checking if nawk is broken... no
checking whether to enable pcntl support... yes, shared
checking for fork... yes
checking for waitpid... yes
checking for sigaction... yes
checking for getpriority... yes
checking for setpriority... yes
checking for wait3... yes
checking for wait4... yes
checking for sigprocmask... yes
checking for sigwaitinfo... yes
checking for sigtimedwait... yes
checking for siginfo_t... yes
checking for ld used by cc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... yes
checking for /usr/bin/ld option to reload object files... -r
checking for BSD-compatible nm... /usr/bin/nm -B
checking whether ln -s works... yes
checking how to recognize dependent libraries... pass_all
checking for ANSI C header files... yes
checking for sys/types.h... yes
checking for sys/stat.h... yes
checking for stdlib.h... yes
checking for string.h... yes
checking for memory.h... yes
checking for strings.h... yes
checking for inttypes.h... yes
checking for stdint.h... yes
checking for unistd.h... yes
checking dlfcn.h usability... yes
checking dlfcn.h presence... yes
checking for dlfcn.h... yes
checking the maximum length of command line arguments... 1572864
checking command to parse /usr/bin/nm -B output from cc object... ok
checking for objdir... .libs
checking for ar... ar
checking for ranlib... ranlib
checking for strip... strip
checking if cc supports -fno-rtti -fno-exceptions... no
checking for cc option to produce PIC... -fPIC
checking if cc PIC flag -fPIC works... yes
checking if cc static flag -static works... yes
checking if cc supports -c -o file.o... yes
checking whether the cc linker (/usr/bin/ld -m elf_x86_64) supports shared libraries... yes
checking whether -lc should be explicitly linked in... no
checking dynamic linker characteristics... GNU/Linux ld.so
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... no

creating libtool
appending configuration tag "CXX" to libtool
configure: creating ./config.status
config.status: creating config.h
/bin/bash /usr/src/php/ext/pcntl/libtool --mode=compile cc -DHAVE_STRUCT_SIGINFO_T -I. -I/usr/src/php/ext/pcntl -DPHP_ATOM_INC -I/usr/src/php/ext/pcntl/include -I/usr/src/php/ext/pcntl/main -I/usr/src/php/ext/pcntl -I/usr/local/include/php -I/usr/local/include/php/main -I/usr/local/include/php/TSRM -I/usr/local/include/php/Zend -I/usr/local/include/php/ext -I/usr/local/include/php/ext/date/lib  -fstack-protector-strong -fpic -fpie -O2 -DHAVE_CONFIG_H  -fstack-protector-strong -fpic -fpie -O2   -c /usr/src/php/ext/pcntl/pcntl.c -o pcntl.lo 
mkdir .libs
 cc -DHAVE_STRUCT_SIGINFO_T -I. -I/usr/src/php/ext/pcntl -DPHP_ATOM_INC -I/usr/src/php/ext/pcntl/include -I/usr/src/php/ext/pcntl/main -I/usr/src/php/ext/pcntl -I/usr/local/include/php -I/usr/local/include/php/main -I/usr/local/include/php/TSRM -I/usr/local/include/php/Zend -I/usr/local/include/php/ext -I/usr/local/include/php/ext/date/lib -fstack-protector-strong -fpic -fpie -O2 -DHAVE_CONFIG_H -fstack-protector-strong -fpic -fpie -O2 -c /usr/src/php/ext/pcntl/pcntl.c  -fPIC -DPIC -o .libs/pcntl.o
/bin/bash /usr/src/php/ext/pcntl/libtool --mode=compile cc -DHAVE_STRUCT_SIGINFO_T -I. -I/usr/src/php/ext/pcntl -DPHP_ATOM_INC -I/usr/src/php/ext/pcntl/include -I/usr/src/php/ext/pcntl/main -I/usr/src/php/ext/pcntl -I/usr/local/include/php -I/usr/local/include/php/main -I/usr/local/include/php/TSRM -I/usr/local/include/php/Zend -I/usr/local/include/php/ext -I/usr/local/include/php/ext/date/lib  -fstack-protector-strong -fpic -fpie -O2 -DHAVE_CONFIG_H  -fstack-protector-strong -fpic -fpie -O2   -c /usr/src/php/ext/pcntl/php_signal.c -o php_signal.lo 
 cc -DHAVE_STRUCT_SIGINFO_T -I. -I/usr/src/php/ext/pcntl -DPHP_ATOM_INC -I/usr/src/php/ext/pcntl/include -I/usr/src/php/ext/pcntl/main -I/usr/src/php/ext/pcntl -I/usr/local/include/php -I/usr/local/include/php/main -I/usr/local/include/php/TSRM -I/usr/local/include/php/Zend -I/usr/local/include/php/ext -I/usr/local/include/php/ext/date/lib -fstack-protector-strong -fpic -fpie -O2 -DHAVE_CONFIG_H -fstack-protector-strong -fpic -fpie -O2 -c /usr/src/php/ext/pcntl/php_signal.c  -fPIC -DPIC -o .libs/php_signal.o
/bin/bash /usr/src/php/ext/pcntl/libtool --mode=link cc -DPHP_ATOM_INC -I/usr/src/php/ext/pcntl/include -I/usr/src/php/ext/pcntl/main -I/usr/src/php/ext/pcntl -I/usr/local/include/php -I/usr/local/include/php/main -I/usr/local/include/php/TSRM -I/usr/local/include/php/Zend -I/usr/local/include/php/ext -I/usr/local/include/php/ext/date/lib  -fstack-protector-strong -fpic -fpie -O2 -DHAVE_CONFIG_H  -fstack-protector-strong -fpic -fpie -O2  -Wl,-O1 -Wl,--hash-style=both -pie -o pcntl.la -export-dynamic -avoid-version -prefer-pic -module -rpath /usr/src/php/ext/pcntl/modules  pcntl.lo php_signal.lo 
cc -shared  .libs/pcntl.o .libs/php_signal.o   -Wl,-O1 -Wl,--hash-style=both -Wl,-soname -Wl,pcntl.so -o .libs/pcntl.so
creating pcntl.la
(cd .libs && rm -f pcntl.la && ln -s ../pcntl.la pcntl.la)
/bin/bash /usr/src/php/ext/pcntl/libtool --mode=install cp ./pcntl.la /usr/src/php/ext/pcntl/modules
cp ./.libs/pcntl.so /usr/src/php/ext/pcntl/modules/pcntl.so
cp ./.libs/pcntl.lai /usr/src/php/ext/pcntl/modules/pcntl.la
PATH="$PATH:/sbin" ldconfig -n /usr/src/php/ext/pcntl/modules
----------------------------------------------------------------------
Libraries have been installed in:
   /usr/src/php/ext/pcntl/modules

If you ever happen to want to link against installed libraries
in a given directory, LIBDIR, you must either use libtool, and
specify the full pathname of the library, or use the `-LLIBDIR'
flag during linking and do at least one of the following:
   - add LIBDIR to the `LD_LIBRARY_PATH' environment variable
     during execution
   - add LIBDIR to the `LD_RUN_PATH' environment variable
     during linking
   - use the `-Wl,--rpath -Wl,LIBDIR' linker flag
   - have your system administrator add LIBDIR to `/etc/ld.so.conf'

See any operating system documentation about shared libraries for
more information, such as the ld(1) and ld.so(8) manual pages.
----------------------------------------------------------------------

Build complete.
Don't forget to run 'make test'.

Installing shared extensions:     /usr/local/lib/php/extensions/no-debug-non-zts-20170718/
find . -name \*.gcno -o -name \*.gcda | xargs rm -f
find . -name \*.lo -o -name \*.o | xargs rm -f
find . -name \*.la -o -name \*.a | xargs rm -f
find . -name \*.so | xargs rm -f
find . -name .libs -a -type d|xargs rm -rf
rm -f libphp.la       modules/* libs/*
root@fb9df8acc0c9:/# php -m
[PHP Modules]
Core
ctype
curl
date
dom
fileinfo
filter
ftp
hash
iconv
json
libxml
mbstring
mysqlnd
openssl
pcntl
pcre
PDO
pdo_sqlite
Phar
posix
readline
Reflection
session
SimpleXML
sodium
SPL
sqlite3
standard
tokenizer
xml
xmlreader
xmlwriter
zlib

[Zend Modules]

[renatomefi]

@yosifkit thanks for your answer, I've been enabling it as you said.
My line of thinking is more on why wouldn't it be enabled by default? We area talking about docker containers where it holds a CLI application which should be able to listen to the posix signals. I do believe that a large portion of people using this in production are probably enabling this extension.
I just believe it's a good default to have!

[tianon]

We've traditionally shied away from allowing for "commonly installed" to be a justification because that opens the door to much broader interpretation (and is much harder to verify), which is why the image as-is only contains the most basic set (especially since users cannot remove them after the fact if they don't need them -- that space is now taken up whether they like it or not).

The ones we currently explicitly include are almost all there simply because they're not possible or are very difficult to compile after-the-fact.

[yosifkit]

Closing for the reasons noted above -- this is trivial to add after-the-fact.