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

[Christophe de Dinechin]

> On 8 Nov 2017, at 16:02, Frediano Ziglio <fziglio at redhat.com> 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
> +#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

I would add a ‘static’ here in the unlikely case someone uses the defer macro twice from the same line in different files.

> +#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 {

Why not keep the old if(streamfd >= 0) test?

> +        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__);
> -- 
> 2.13.6
> 
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