This is an attempt to make a C API that resembles the C++
std::unique_lock (mostly untested). The idea is that you can write
QEMU_LOCK_GUARD(QemuMutex, guard_name, &some_mutex);
instead of
qemu_mutex_lock(&some_mutex);
...
out:
qemu_mutex_unlock(&some_mutex);
and the mutex will be unlocked on all exit paths. In C++ that
would be "std::unique_lock<QemuMutex> guard_name(some_mutex);".
Likewise,
QEMU_WITH_LOCK(QemuMutex, guard_name, &some_mutex) {
...
}
is the same as
qemu_mutex_lock(&some_mutex);
...
qemu_mutex_unlock(&some_mutex);
except that any returns within the region will unlock the mutex.
It's possible to use QemuLockGuard also with a spinlock or a
CoMutex. However, it is _not_ possible to return a QemuLockGuard
since C doesn't have an equivalent of C++'s "move semantics", so
there are other "constructor" macros such as QEMU_ADOPT_LOCK
and QEMU_TAKEN_LOCK.
On the positive side, I checked that the entire abstraction
is removed by the compiler, the generated code is more or less
the same. Also, it would let us for example change block/curl.c
to use a CoQueue instead of a home-grown list+QemuMutex.
However, I am still not sure about the readability, and it doesn't play
well with another common idiom in QEMU, which is to wrap global mutexes
with function such as
static void block_job_lock(void)
{
qemu_mutex_lock(&block_job_mutex);
}
static void block_job_unlock(void)
{
qemu_mutex_unlock(&block_job_mutex);
}
So I'm a bit underwhelmed by this experiment. Other opinions?
Paolo
Paolo Bonzini (5):
compiler: add a helper for C99 inline functions
lock-guard: add scoped lock implementation
qemu-timer: convert to use lock guards
qht: convert to use lock guards
thread-pool: convert to use lock guards
include/qemu/compiler.h | 15 +++++++
include/qemu/coroutine.h | 4 ++
include/qemu/lock-guard.h | 99 +++++++++++++++++++++++++++++++++++++++++++++++
include/qemu/thread.h | 7 ++++
util/Makefile.objs | 1 +
util/qemu-thread.c | 17 ++++++++
util/qemu-timer.c | 84 ++++++++++++++++++++--------------------
util/qht.c | 59 ++++++++++++++--------------
util/thread-pool.c | 26 ++++++-------
9 files changed, 225 insertions(+), 87 deletions(-)
create mode 100644 include/qemu/lock-guard.h
create mode 100644 util/qemu-thread.c
--
2.14.3
