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Comparing ray/src/common/rtprocess.h (file contents):
Revision 3.18 by greg, Fri Feb 28 05:18:49 2020 UTC vs.
Revision 3.19 by greg, Fri Feb 28 16:23:47 2020 UTC

# Line 58 | Line 58 | extern "C" {
58     on the output of the parent.  Make sure to call fflush(stdout) first
59     if any data was buffered.  It is illegal to set both PF_FILT_INP and
60     PF_FILT_OUT, as a circular process is guaranteed to hang.
61 +  
62 +   If you want behavior similar to popen(cmd, "w") (again Unix-only),
63 +   keeping stdout open in parent, use a duplicate descriptor like so:
64 +   {
65 +        SUBPROC rtp = sp_inactive;
66 +        FILE    *fout;
67 +        fflush(stdout);
68 +        rtp.w = dup(fileno(stdout));
69 +        rtp.flags |= PF_FILT_OUT;
70 +        if (open_process(&rtp, cmd_argv) <= 0) {
71 +                perror(cmd_argv[0]); exit(1);
72 +        }
73 +        fout = fdopen(rtp.w, "w");
74 +        ...write data to filter using fout until finished...
75 +        fclose(fout);
76 +        if (close_process(&rtp)) {
77 +                perror(cmd_argv[0]); exit(1);
78 +        }
79 +        ...can continue sending data directly to stdout...
80 +    }
81 +    We could also have called open_process() after fdopen() above, or after
82 +    using fopen() on a file if we wanted to insert our filter before it.
83 +    A similar sequence may be used to filter from stdin without closing
84 +    it, though process termination becomes more difficult with two readers.
85 +    Filtering input from a file works better, since the file is then read by
86 +    the child only, as in:
87 +    {
88 +        SUBPROC rtp = sp_inactive;
89 +        FILE    *fin = fopen(fname, "r");
90 +        if (fin == NULL) {
91 +                open_error(fname); exit(1);
92 +        }
93 +        rtp.r = fileno(fin);
94 +        rtp.flags |= PF_FILT_INP;
95 +        if (open_process(&rtp, cmd_argv) <= 0) {
96 +                perror(cmd_argv[0]); fclose(fin); exit(1);
97 +        }
98 +        ...read filtered file data from fin until EOF...
99 +        fclose(fin);
100 +        if (close_process(&rtp)) {
101 +                perror(cmd_argv[0]); exit(1);
102 +        }
103 +    }
104   */
105  
106  

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