[Spice-devel] [PATCH spice-streaming-server 1/3] Use defer style destruction instead of old C style and goto

[Frediano Ziglio]

> 
> On Wed, Nov 08, 2017 at 03:02:35PM +0000, Frediano Ziglio wrote:
> > This better integrate with exceptions.
> > Also don't leak resources using a return in the middle of the
> > code.
> > 
> > Signed-off-by: Frediano Ziglio <fziglio at redhat.com>
> > ---
> >  src/Makefile.am               |  1 +
> >  src/defer.hpp                 | 16 ++++++++++++++++
> >  src/spice-streaming-agent.cpp | 16 ++++++++--------
> >  3 files changed, 25 insertions(+), 8 deletions(-)
> >  create mode 100644 src/defer.hpp
> > 
> > diff --git a/src/Makefile.am b/src/Makefile.am
> > index 8d5c5bd..ec1969a 100644
> > --- a/src/Makefile.am
> > +++ b/src/Makefile.am
> > @@ -56,4 +56,5 @@ spice_streaming_agent_SOURCES = \
> >  	mjpeg-fallback.cpp \
> >  	jpeg.cpp \
> >  	jpeg.hpp \
> > +	defer.hpp \
> >  	$(NULL)
> > diff --git a/src/defer.hpp b/src/defer.hpp
> > new file mode 100644
> > index 0000000..93931fe
> > --- /dev/null
> > +++ b/src/defer.hpp
> > @@ -0,0 +1,16 @@
> > +// see
> > https://stackoverflow.com/questions/32432450/what-is-standard-defer-finalizer-implementation-in-c
> 
> Is there any license associated with that code snippet?
> 
> Christophe
> 

Good question, looks like MIT, see https://meta.stackexchange.com/questions/271080/the-mit-license-clarity-on-using-code-on-stack-overflow-and-stack-exchange

Frediano

> > +#ifndef defer
> > +template <class F> struct deferrer
> > +{
> > +    F f;
> > +    ~deferrer() { f(); }
> > +};
> > +struct defer_dummy {};
> > +template <class F> inline deferrer<F> operator*(defer_dummy, F f)
> > +{
> > +    return {f};
> > +}
> > +#define DFRCAT_(LINE) _defer##LINE
> > +#define DFRCAT(LINE) DFRCAT_(LINE)
> > +#define defer auto DFRCAT(__LINE__) = defer_dummy{} *[&]() -> void
> > +#endif
> > diff --git a/src/spice-streaming-agent.cpp b/src/spice-streaming-agent.cpp
> > index ed7ddb9..4122eee 100644
> > --- a/src/spice-streaming-agent.cpp
> > +++ b/src/spice-streaming-agent.cpp
> > @@ -33,6 +33,7 @@
> >  
> >  #include "hexdump.h"
> >  #include "concrete-agent.hpp"
> > +#include "defer.hpp"
> >  
> >  using namespace std;
> >  using namespace SpiceStreamingAgent;
> > @@ -353,12 +354,17 @@ do_capture(const char *streamport, FILE *f_log)
> >          // TODO was syslog(LOG_ERR, "Failed to open %s: %s\n", streamport,
> >          strerror(errno));
> >          throw std::runtime_error("failed to open streaming device");
> >  
> > +    defer {
> > +        close(streamfd);
> > +        streamfd = -1;
> > +    };
> > +
> >      unsigned int frame_count = 0;
> >      while (! quit) {
> >          while (!quit && !streaming_requested) {
> >              if (read_command(1) < 0) {
> >                  syslog(LOG_ERR, "FAILED to read command\n");
> > -                goto done;
> > +                return;
> >              }
> >          }
> >  
> > @@ -409,19 +415,13 @@ do_capture(const char *streamport, FILE *f_log)
> >              //usleep(1);
> >              if (read_command(0) < 0) {
> >                  syslog(LOG_ERR, "FAILED to read command\n");
> > -                goto done;
> > +                return;
> >              }
> >              if (!streaming_requested) {
> >                  capture->Reset();
> >              }
> >          }
> >      }
> > -
> > -done:
> > -    if (streamfd >= 0) {
> > -        close(streamfd);
> > -        streamfd = -1;
> > -    }
> >  }
> >  
> >  #define arg_error(...) syslog(LOG_ERR, ## __VA_ARGS__);