• Kevin Wolf's avatar
    coroutine: introduce coroutines · 00dccaf1
    Kevin Wolf authored
    Asynchronous code is becoming very complex.  At the same time
    synchronous code is growing because it is convenient to write.
    Sometimes duplicate code paths are even added, one synchronous and the
    other asynchronous.  This patch introduces coroutines which allow code
    that looks synchronous but is asynchronous under the covers.
    
    A coroutine has its own stack and is therefore able to preserve state
    across blocking operations, which traditionally require callback
    functions and manual marshalling of parameters.
    
    Creating and starting a coroutine is easy:
    
      coroutine = qemu_coroutine_create(my_coroutine);
      qemu_coroutine_enter(coroutine, my_data);
    
    The coroutine then executes until it returns or yields:
    
      void coroutine_fn my_coroutine(void *opaque) {
          MyData *my_data = opaque;
    
          /* do some work */
    
          qemu_coroutine_yield();
    
          /* do some more work */
      }
    
    Yielding switches control back to the caller of qemu_coroutine_enter().
    This is typically used to switch back to the main thread's event loop
    after issuing an asynchronous I/O request.  The request callback will
    then invoke qemu_coroutine_enter() once more to switch back to the
    coroutine.
    
    Note that if coroutines are used only from threads which hold the global
    mutex they will never execute concurrently.  This makes programming with
    coroutines easier than with threads.  Race conditions cannot occur since
    only one coroutine may be active at any time.  Other coroutines can only
    run across yield.
    
    This coroutines implementation is based on the gtk-vnc implementation
    written by Anthony Liguori <anthony@codemonkey.ws> but it has been
    significantly rewritten by Kevin Wolf <kwolf@redhat.com> to use
    setjmp()/longjmp() instead of the more expensive swapcontext() and by
    Paolo Bonzini <pbonzini@redhat.com> for Windows Fibers support.
    Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
    Signed-off-by: default avatarStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
    00dccaf1
qemu-coroutine.c 1.57 KB