1flockfile(3C)            Standard C Library Functions            flockfile(3C)
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NAME

6       flockfile, funlockfile, ftrylockfile - acquire and release stream lock
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SYNOPSIS

9       #include <stdio.h>
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11       void flockfile(FILE *stream);
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14       void funlockfile(FILE *stream);
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17       int ftrylockfile(FILE *stream);
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DESCRIPTION

21       The  flockfile() function acquires an internal lock of a stream stream.
22       If the lock is already acquired by another thread, the  thread  calling
23       flockfile()  is  suspended  until it can acquire the lock.  In the case
24       that the stream lock is available, flockfile() not  only  acquires  the
25       lock,  but keeps track of the number of times it is being called by the
26       current thread.  This implies that the stream lock can be acquired more
27       than once by the same thread.
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30       The  funlockfile() function releases the lock being held by the current
31       thread.  In the case of recursive locking, this function must be called
32       the  same  number of times flockfile() was called.  After the number of
33       funlockfile() calls is equal to the number of  flockfile()  calls,  the
34       stream lock is available for other threads to acquire.
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37       The  ftrylockfile()  function  acquires  an  internal  lock of a stream
38       stream, only if that object is available.  In essence ftrylockfile() is
39       a non-blocking version of flockfile().
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RETURN VALUES

42       The  ftrylockfile() function returns 0 on success and non-zero to indi‐
43       cate a lock cannot be acquired.
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EXAMPLES

46       Example 1 A sample program of flockfile().
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49       The following example prints everything out  together,  blocking  other
50       threads  that  might  want  to  write to the same file between calls to
51       fprintf(3C):
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54         FILE iop;
55         flockfile(iop);
56         fprintf(iop, "hello ");
57         fprintf(iop, "world);
58         fputc(iop, 'a');
59         funlockfile(iop);
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63       An unlocked interface is available in case  performance  is  an  issue.
64       For example:
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67         flockfile(iop);
68         while (!feof(iop)) {
69                 *c++ = getc_unlocked(iop);
70         }
71         funlockfile(iop);
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ATTRIBUTES

75       See attributes(5) for descriptions of the following attributes:
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80       ┌─────────────────────────────┬─────────────────────────────┐
81       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
82       ├─────────────────────────────┼─────────────────────────────┤
83       │Interface Stability          │Standard                     │
84       ├─────────────────────────────┼─────────────────────────────┤
85       │MT-Level                     │MT-Safe                      │
86       └─────────────────────────────┴─────────────────────────────┘
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SEE ALSO

89       Intro(3),   __fsetlocking(3C),   ferror(3C),   fprintf(3C),   getc(3C),
90       putc(3C), stdio(3C), ungetc(3C), attributes(5), standards(5)
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NOTES

93       The interfaces on this page  are as specified in IEEE Std  1003.1:2001.
94       See standards(5).
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98SunOS 5.11                        10 Sep 2003                    flockfile(3C)
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