The existing singlethread g_spawn_sync test is modified and now tests
that special characters in arguments are correctly passed to child.
The test is added before spawn escaping fixing on win32
and covers the case currently broken on win32:
'trailing \ in argument containing space'.
Philip Withnall suggests that glib should treat all negative
file descriptors as unset/invalid, rather than explicitly requiring
them to be -1.
This can simplify the logic for some users of this code.
https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/132
When the amount of free memory on the system is somewhat low, gnome-shell
will sometimes fail to launch apps, reporting the error:
fork(): Cannot allocate memory
fork() is failing here because while cloning the process virtual address
space, Linux worries that the thread being forked may end up COWing the
entire address space of the parent process (gnome-shell, which is
memory-hungry), and there is not enough free memory to permit that to
happen.
In this case we are simply calling fork() in order to quickly call exec(),
which will throw away the entirity of the duplicated VM, so we should
look for ways to avoid the overcommit check.
The well known solution to this is to use clone(CLONE_VM) or vfork(), which
completely avoids creating a new memory address space for the child.
However, that comes with a bunch of caveats and complications:
https://gist.github.com/nicowilliams/a8a07b0fc75df05f684c23c18d7db234https://ewontfix.com/7/
In 2016, glibc's posix_spawn() was rewritten to use this approach
while also resolving the concerns.
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=9ff72da471a509a8c19791efe469f47fa6977410
I experimented with a similar approach in glib, but it was not practical
because glibc has several items of important internal knowledge (such as
knowing which signals should be given special treatment because they are
NPTL implementation details) that are not cleanly exposed elsewhere.
Instead, this patch adapts the gspawn code to use posix_spawn() where
possible, which will reap the benefits of that implementation.
The posix_spawn API is more limited than the gspawn API though,
partly due to natural limitations of using CLONE_VM, so the posix_spawn
path is added as a separate codepath which is only executed when the
conditions are right. Callers such as gnome-shell will have to be modified
to meet these conditions, such as not having a child_setup function.
In addition to allowing for the gnome-shell "Cannot allocate memory"
failure to be avoided, this should result in a general speedup in this
area, because fork()'s behaviour of cloning the entire VM space
has a cost which is now avoided. posix_spawn() has also recently
been optimized on OpenSolaris as the most performant way to spawn
a child process.
Add a new process spawning function variant which allows the caller
to pass specific file descriptors for stdin, stdout and stderr.
It is otherwise identical to g_spawn_async_with_pipes.
Allow the same fd to be passed in multiple parameters. To make this
workable, the child process logic that closes the fd after the first time
it has been dup2'ed needed tweaking; we now just set those fds to be
closed upon exec using the CLOEXEC flag. Add a test for this case.
This will be used by gnome-shell to avoid performing equivalent
dup2 actions in a child_setup function. Dropping use of child_setup will
enable use of an upcoming optimized process spawning codepath.
A slightly modified patch originally written by Morten Welinder
<terra@gnome.org> to make the error codes returned by g_spawn_*()
functions more specific when on Windows. They are already this specific
on Linux.
Add a unit test for the ENOENT case.
https://gitlab.gnome.org/GNOME/glib/issues/303
Signed-off-by: Philip Withnall <withnall@endlessm.com>
Use a Windows-style .bat script for the test_spawn_script() test, at least
when the code is built with Visual C++ (due to differences in how scripts
are written for shells and Windows cmd.exe), and account for Windows-style
line endings for that test too.
Let the MinGW builds (which are normally done in an MSYS BASH-style shell) continue to use the
*NIX-style script for that test.
https://bugzilla.gnome.org/show_bug.cgi?id=711047
This should be the last users that need to be ported.
For some of the oldschool non-gtester-ified tests, we call g_test_init()
from main() because it is necessary in order to use
g_test_build_filename().
Add a test that excercises the script execution code.
Unfortunately, much of this code only runs in the forked
child, and therefore its execution does not get caught
by gcov.
