Safe operating-system calls
The following table lists operating-system calls that are considered safe within a well-behaved C UDR on all supported platforms. Be sure to use threadsafe (_r) versions where applicable.
| Category | System calls | Notes® |
|---|---|---|
| Character classification | isalnum(), isalpha(), isascii(), isastream(), isatty(), iscntrl(), isdigit(), isgraph(), islower(), isspace(), isprint(), ispunct(), isupper(), isxdigit() | None |
| String manipulation | tolower(), toupper(), toascii() | None |
| String parsing | getopt(), getsubopt() | None |
| Multibyte strings | mbtowc(), wctomb(), mblen(), mbstowcs(), wcstombs() | None. |
| String processing | strcasecmp(), strcat(), strchr(), strcmp(), strcoll(), strcpy(), strcspn(), strdup(), strerror(), strlen(), strncasecmp(), strncat(), strncmp(), strncpy(), strpbrk(), strrchr(), strsignal(), strspn(), strstr(), strtod(), strtok(), strtok_r(), strtol(), strtoll(), strtoul(), strtoull(), strxfrm() | None. |
| String formatting | sprintf(), sscanf() | None |
| Numeric processing | a641(), l64a(), abs(), labs(), llabs(), atof(), atoi(), atol(), atoll(), div(), ldiv(), lldiv(), lltostr(), strtoll() | None |
| Random-number generation | srand(), rand(), srandom(), random(), srand48(), drand48(), erand48(), lrand48(), nrand48(), mrand48() | The random-number generator must be reseeded whenever a thread switch might have occurred. |
| Numeric conversion | econvert(), fconvert(), gconvert(), seconverty(), sfconvert(), sgconvert(), qeconvert(), qfconvert(), ecvt(), fcvt(), gcvt() | ifx_dececvt(), ifx_decfcvt() |
| Time functions | ascftime(), strftime(), cftime(), ctime(), ctime_r(), asctime(), asctime_r(), gmtime(), gmtime_r(), difftime(), localtime(), localtime_r()clock(), gettimeofday(), mktime() | No time-zone changes are permitted. |
| Date functions | getdate() | None |
| Sorting and searching | bsearch(), qsort(), lfind(), lsearch() | None |
| Encryption | crypt(), setkey(), encrypt() | None |
| Memory management | memccpy(), memchr(), memcmp(), memcpy(), memmove(), memset() | Use memmove() and memset() only for memory that was allocated with mi_alloc(). |
| Environment information | getenv() | None |
| Bit manipulation | ffs() | None |
| Byte manipulation | swab() | None |
| Structure-member manipulation | offsetof() | None |
| Trigonometric functions | acos(), acosh(), asin(), asinh(), atan(), atan2(), atanh()cos(), cosh(), sin(), sinh(), tan(), tanh() | None |
| Bessel functions | j0(), j1(), jn(), y0(), y1(), yn() | None |
| Root extraction | cbrt(), sqrt() | None |
| Rounding | ceil(), floor(), rint() | None |
| IEEE functions | copysign(), isnan(), fabs(), fmod(), nextafter(), remainder() | None |
| Error functions | erf(), erfc() | None |
| Exponentials and logarithms | exp(), expm1(), log(), log10(), log1p(), pow() | None |
| Gamma functions | lgamma(), lgamma_r() | The contents of signgam are unreliable after a thread switch. |
| Euclidean distance | hypot() | None |
Tip: The system calls in the preceding table
follow the Portable Operating System Interface for Computing Environments
(POSIX) specification.
For a list of categories of operating-system calls that are generally unsafe in a UDR, see Unsafe operating-system calls.
The following actions are valid only in C UDRs that run
on Windows and only if they
do not interfere with the shared-memory model that the database server
uses:
- C UDRs can create additional threads or processes.
- C UDRs can use shared memory for interprocess communication.
Important: Use of user-defined VPs can result
in slightly lower performance because the thread must migrate from
the CPU VP to the user-defined VP on which the C UDR executes. Use
a user-defined VP only when necessary.