[Qemu-devel] [PATCH 0/4] coroutine-lock: polymorphic CoQueue

[Paolo Bonzini <pbonzini@redhat.com>]

There are cases in which a queued coroutine must be restarted from
non-coroutine context (with qemu_co_enter_next).  In this cases,
qemu_co_enter_next also needs to be thread-safe, but it cannot use a
CoMutex and so cannot qemu_co_queue_wait.  This happens in curl (which
right now is rolling its own list of Coroutines) and will happen in
Fam's NVMe driver as well.

This series extracts the idea of a polymorphic lockable object
from my "scoped lock guard" proposal, and applies it to CoQueue.
The implementation of QemuLockable is similar to C11 _Generic, but
redone using the preprocessor and GCC builtins for compatibility.

In general, while a bit on the esoteric side, the functionality used
to emulate _Generic is fairly old in GCC, and the builtins are already
used by include/qemu/atomic.h; the series was tested with Fedora 27 (boot
Damn Small Linux via http) and CentOS 6 (compiled only).

Paolo

Paolo Bonzini (4):
  lockable: add QemuLockable
  coroutine-lock: convert CoQueue to use QemuLockable
  coroutine-lock: make qemu_co_enter_next thread-safe
  curl: convert to CoQueue

 block/curl.c                | 20 +++---------
 fsdev/qemu-fsdev-throttle.c |  4 +--
 include/qemu/compiler.h     | 40 ++++++++++++++++++++++++
 include/qemu/coroutine.h    | 25 ++++++++++-----
 include/qemu/lockable.h     | 75 +++++++++++++++++++++++++++++++++++++++++++++
 include/qemu/thread.h       |  5 ++-
 include/qemu/typedefs.h     |  4 +++
 util/qemu-coroutine-lock.c  | 22 ++++++++-----
 8 files changed, 159 insertions(+), 36 deletions(-)
 create mode 100644 include/qemu/lockable.h

-- 
2.14.3