Re: [PATCH] simple-ipc: correct ifdefs when NO_PTHREADS is defined

[Jeff Hostetler <git@jeffhostetler.com>]

On 5/18/21 8:48 PM, Junio C Hamano wrote:
> "Jeff Hostetler via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
>> +# Simple-ipc requires threads and platform-specific IPC support.
>> +# (We group all Unix variants in the top-level else because Windows
>> +# also defines NO_UNIX_SOCKETS.)
>>   ifdef USE_WIN32_IPC
>> +	BASIC_CFLAGS += -DSUPPORTS_SIMPLE_IPC
>>   	LIB_OBJS += compat/simple-ipc/ipc-shared.o
>>   	LIB_OBJS += compat/simple-ipc/ipc-win32.o
>> +else
>> +ifndef NO_PTHREADS
>> +ifndef NO_UNIX_SOCKETS
>> +	BASIC_CFLAGS += -DSUPPORTS_SIMPLE_IPC
>> +	LIB_OBJS += compat/simple-ipc/ipc-shared.o
>> +	LIB_OBJS += compat/simple-ipc/ipc-unix-socket.o
>> +endif
>> +endif
> 
> OK, so "!defined(NO_PTHREADS) && !defined(NO_UNIX_SOCKETS)" is the
> requirement for SIMPLE_IPC unless you are on Windows.
> 
>> diff --git a/compat/simple-ipc/ipc-unix-socket.c b/compat/simple-ipc/ipc-unix-socket.c
>> index 38689b278df3..c23b17973983 100644
>> --- a/compat/simple-ipc/ipc-unix-socket.c
>> +++ b/compat/simple-ipc/ipc-unix-socket.c
>> @@ -6,10 +6,16 @@
>>   #include "unix-socket.h"
>>   #include "unix-stream-server.h"
>>   
>> +#ifdef SUPPORTS_SIMPLE_IPC
>> +
>>   #ifdef NO_UNIX_SOCKETS
>>   #error compat/simple-ipc/ipc-unix-socket.c requires Unix sockets
>>   #endif
>>   
>> +#ifdef NO_PTHREADS
>> +#error compat/simple-ipc/ipc-unix-socket.c requires pthreads
>> +#endif
>> +
> 
> Do we want to duplicate the requirement here and risk them drifting
> apart?
> 
>> @@ -997,3 +1003,5 @@ void ipc_server_free(struct ipc_server_data *server_data)
>>   	free(server_data->fifo_fds);
>>   	free(server_data);
>>   }
>> +
>> +#endif /* SUPPORTS_SIMPLE_IPC */
> 
> If anything, I do not think we want a huge #ifdef/#endif around the
> whole file.  Feeding this source to your compiler when these three C
> proprocessor macros do not agree with its use is an error, so perhaps
> lose all of these #ifdef/#endif around the three macros and refer human
> readers to the top-level Makefile with a comment, e.g.
> 
> /*
>   * Non Windows platforms need !NO_UNIX_SOCKETS and !NO_PTHREADS
>   * to compile and use this file.  See the top-level Makefile.
>   */
> 
> if we really wanted to have a way to help builders identify the
> reason why their build is failing.
> 

Would it be better to just have something like the following at the
top of the source files and leave the details to the Makefile:


#ifndef SUPPORTS_SIMPLE_IPC
/*
  * This source file should only be included when Simple IPC
  * is supported.  See the top-level Makefile.
  */
#error SUPPORTS_SIMPLE_IPC not defined
#endif