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
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.
