1gd_open_limit(3) GETDATA gd_open_limit(3)
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14 gd_open_limit — set a Dirfile's allowed number of open files
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18 #include <getdata.h>
19 long gd_open_limit(DIRFILE *dirfile, long limit);
21
24 The gd_open_limit() function can be used to limit the number of RAW
25 file descriptors which GetData simultaneously holds open in the open
26 dirfile(5) database specified by dirfile. This function can also be
27 used to report the current number of open files, or the current limit.
28 When limiting is active, to stay below the limit, GetData will automat‐
29 ically close the least recently accessed RAW fields (as if
30 gd_raw_close(3) were called), when needed.
31 The default value for the limit is zero, indicating that limiting is
33 disabled. In this case, GetData will never automatically close open
34 RAW fields. To enable limiting call this function with a positive val‐
35 ue for limit. If limited, the minimum limit is two; if this function
36 is passed a limit of one, it will behave as if the value 2 were passed
37 instead.
38 When setting a limit, this function will immediately close enough RAW
40 fields to remain below the specified limit.
41 The argument limit may alternately be one of the following special val‐
43 ues:
44 GD_OLIMIT_NONE (=0)
46 Disable limiting, if it was previously active.
47 GD_OLIMIT_CURRENT
49 Do nothing other than report the current limit. This is equiv‐
50 alent to calling this function with limit equal to the current
51 limit.
52 GD_OLIMIT_COUNT
54 Instead of returning the current limit, return the current num‐
55 ber filed descriptors for this dirfile. The current limit is
56 not changed.
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60 If limit is GD_OLIMIT_COUNT, then the current number of file descrip‐
61 tors in use by this dirfile is returned, or zero if limiting is dis‐
62 abled (i.e. the limit is zero).
63 For other values of limit, if successful, this function returns the
65 open field limit, after possibly modifying it. This limit is never
66 negative. It will be zero if limiting is disabled.
67 If limit is one of the special values GD_OLIMIT_COUNT, GD_OLIMIT_CUR‐
69 RENT, or GD_OLIMIT_NONE (=0), then this function always succeeds. Oth‐
70 erwise, on error, gd_open_limit() returns a negative-valued error code.
71 Possible error codes are:
72 GD_E_ALLOC
74 The library was unable to allocate memory.
75 GD_E_BAD_DIRFILE
77 The supplied dirfile was invalid.
78 GD_E_IO An I/O error occurred while trying to write modified data to
80 disk as a result in a reduction of the open field limit.
81 The error code is also stored in the DIRFILE object and may be re‐
83 trieved after this function returns by calling gd_error(3). A descrip‐
84 tive error string for the error may be obtained by calling
85 gd_error_string(3).
86
90 The file descriptors tracked by this functionality are only those asso‐
91 ciated with RAW fields which are held open across function calls. Dur‐
92 ing the course of any library call, GetData may temporarily exceed a
93 file descriptor limit set with this function without triggering an au‐
94 tomatic close. Some headroom is always a good idea.
95 Furthermore, this limit is specific to the specified dirfile. It is
97 not a global limit for the whole GetData library. If a process has
98 multiple DIRFILEs open, each of them has its own limit (or is unlimit‐
99 ed), even though they all draw from the same limited pool of file de‐
100 scriptors.
101 In some cases, usually when writing to a compressed RAW field, two file
103 descriptors may be held open for a single field.
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107 The gd_open_limit() function appeared in GetData-0.11.0.
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111 gd_error(3), gd_error_string(3), gd_open(3), gd_raw_close(3),
112 getrlimit(3), ulimit(3), dirfile(5)
113Version 0.11.0 5 October 2017 gd_open_limit(3)