Even though pthreads doesn't support this, there are various alternative
APIs that use this. For example, uv_cond_timedwait() accepts a relative
timeout. So does Rust's std::sync::Condvar::wait_timeout().
Though I personally think that relative timeouts are bad (due to
imprecision for repeated operations), it does seem that people want
this. Extend the existing futex functions to keep track of whether an
absolute timeout is used in a boolean flag.
MFC after: 1 month
Compared to the previous version, v0.16, there are a couple of minor
changes:
- CLOUDABI_AT_PID: Process identifiers for CloudABI processes.
Initially, BSD process identifiers weren't exposed inside the runtime,
due to them being pretty much useless inside of a cluster computing
environment. When jobs are scheduled across systems, the BSD process
number doesn't act as an identifier. Even on individual systems they
may recycle relatively quickly.
With this change, the kernel will now generate a UUIDv4 when executing
a process. These UUIDs can be obtained within the process using
program_getpid(). Right now, FreeBSD will not attempt to store this
value. This should of course happen at some point in time, so that it
may be printed by administration tools.
- Removal of some unused structure members for polling.
With the polling framework being simplified/redesigned, it turns out
some of the structure fields were not used by the C library. We can
remove these to keep things nice and tidy.
Obtained from: https://github.com/NuxiNL/cloudabi
The most important change in this release is the removal of the
poll_fd() system call; CloudABI's equivalent of kevent(). Though I think
that kqueue is a lot saner than many of its alternatives, our
experience is that emulating this system call on other systems
accurately isn't easy. It has become a complex API, even though I'm not
convinced this complexity is needed. This is why we've decided to take a
different approach, by looking one layer up.
We're currently adding an event loop to CloudABI's C library that is API
compatible with libuv (except when incompatible with Capsicum).
Initially, this event loop will be built on top of plain inefficient
poll() calls. Only after this is finished, we'll work our way backwards
and design a new set of system calls to optimize it.
Interesting challenges will include integrating asynchronous I/O into
such a system call API. libuv currently doesn't aio(4) on Linux/BSD, due
to it being unreliable and having undesired semantics.
Obtained from: https://github.com/NuxiNL/cloudabi
Now that all of the packaged software has been adjusted to either use
Flower (https://github.com/NuxiNL/flower) for making incoming/outgoing
network connections or can have connections injected, there is no longer
need to keep accept() around. It is now a lot easier to write networked
services that are address family independent, dual-stack, testable, etc.
Remove all of the bits related to accept(), but also to
getsockopt(SO_ACCEPTCONN).
With Flower (CloudABI's network connection daemon) becoming more
complete, there is no longer any need for creating any unconnected
sockets. Socket pairs in combination with file descriptor passing is all
that is necessary, as that is what is used by Flower to pass network
connections from the public internet to listening processes.
Remove all of the kernel bits that were used to implement socket(),
listen(), bindat() and connectat(). In principle, accept() and
SO_ACCEPTCONN may also be removed, but there are still some consumers
left.
Obtained from: https://github.com/NuxiNL/cloudabi
MFC after: 1 month
The CloudABI specification has had some minor changes over the last half
year. No substantial features have been added, but some features that
are deemed unnecessary in retrospect have been removed:
- mlock()/munlock():
These calls tend to be used for two different purposes: real-time
support and handling of sensitive (cryptographic) material that
shouldn't end up in swap. The former use case is out of scope for
CloudABI. The latter may also be handled by encrypting swap.
Removing this has the advantage that we no longer need to worry about
having resource limits put in place.
- SOCK_SEQPACKET:
Support for SOCK_SEQPACKET is rather inconsistent across various
operating systems. Some operating systems supported by CloudABI (e.g.,
macOS) don't support it at all. Considering that they are rarely used,
remove support for the time being.
- getsockname(), getpeername(), etc.:
A shortcoming of the sockets API is that it doesn't allow you to
create socket(pair)s, having fake socket addresses associated with
them. This makes it harder to test applications or transparently
forward (proxy) connections to them.
With CloudABI, we're slowly moving networking connectivity into a
separate daemon called Flower. In addition to passing around socket
file descriptors, this daemon provides address information in the form
of arbitrary string labels. There is thus no longer any need for
requesting socket address information from the kernel itself.
This change also updates consumers of the generated code accordingly.
Even though system calls end up getting renumbered, this won't cause any
problems in practice. CloudABI programs always call into the kernel
through a kernel-supplied vDSO that has the numbers updated as well.
Obtained from: https://github.com/NuxiNL/cloudabi
Similar to the change for sendmsg(), create a pointer size independent
implementation of recvmsg() and let cloudabi32 and cloudabi64 call into
it. In case userspace requests one or more file descriptors, call
kern_recvit() in such a way that we get the control message headers in
an mbuf. Iterate over all of the headers and copy the file descriptors
to userspace.
Reduce the potential amount of code duplication between cloudabi32 and
cloudabi64 by creating a cloudabi_sock_recv() utility function. The
cloudabi32 and cloudabi64 modules will then only contain code to convert
the iovecs to the native pointer size.
In cloudabi_sock_recv(), we can now construct an SCM_RIGHTS cmsghdr in
an mbuf and pass that on to kern_sendit().
Essentially, this is a literal copy of the code in sys/compat/cloudabi64,
except that it now makes use of 32-bits datatypes and limits. In
sys/conf/files, we now need to take care to build the code in
sys/compat/cloudabi if either COMPAT_CLOUDABI32 or COMPAT_CLOUDABI64 is
turned on.
This change does not yet include any of the CPU dependent bits. Right
now I have implementations for running i386 binaries both on i386 and
x86-64, which I will send out for review separately.
