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269 lines
6.7 KiB
Groff
269 lines
6.7 KiB
Groff
.ds d \-\^\-
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.de DR
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.de See
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See \fB\\$1\fP for details.
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.de SeeIn
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See \fB\\$1\fP in \fB\\$2\fP for details.
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..
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.TH POOL_ALLOC 3
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.SH NAME
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pool_alloc, pool_free, pool_free_old, pool_talloc, pool_tfree, pool_create, pool_destroy, pool_boundary
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\- Allocate and free memory in managed allocation pools.
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.SH SYNOPSIS
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.B #include "pool_alloc.h"
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\fBstruct alloc_pool *pool_create(size_t \fIsize\fB, size_t \fIquantum\fB, void (*\fIbomb\fB)(char *), int \fIflags\fB);
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\fBvoid pool_destroy(struct alloc_pool *\fIpool\fB);
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\fBvoid *pool_alloc(struct alloc_pool *\fIpool\fB, size_t \fIsize\fB, char *\fImsg\fB);
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\fBvoid pool_free(struct alloc_pool *\fIpool\fB, size_t \fIsize\fB, void *\fIaddr\fB);
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\fBvoid pool_free_old(struct alloc_pool *\fIpool\fB, void *\fIaddr\fB);
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\fBvoid *pool_talloc(struct alloc_pool *\fIpool\fB, \fItype\fB), int \fIcount\fB, char *\fImsg\fB);
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\fBvoid pool_tfree(struct alloc_pool *\fIpool\fB, \fItype\fB, int \fIcount\fB, void *\fIaddr\fB);
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\fBvoid pool_boundary(struct alloc_pool *\fIpool\fB, sise_t \fIsize\fB);
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.SH DESCRIPTION
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.P
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The pool allocation routines use
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.B malloc()
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for underlying memory management.
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What allocation pools do is cause memory within a given pool
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to be allocated in large contiguous blocks
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(called extents) that will be reusable when freed. Unlike
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.BR malloc() ,
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the allocations are not managed individually.
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Instead, each extent tracks the total free memory within the
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extent. Each extent can either be used to allocate memory
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or to manage the freeing of memory within that extent.
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When an extent has less free memory than a given
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allocation request, the current extent ceases to be used
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for allocation. See also the
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.B pool_boundary()
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function.
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.P
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This form of memory management is suited to large numbers of small
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related allocations that are held for a while
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and then freed as a group.
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Because the
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underlying allocations are done in large contiguous extents,
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when an extent is freed, it can release a large enough
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contiguous block of memory to allow the memory to be returned
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to the OS for use by whatever program needs it.
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You can allocate from one or more memory pools and/or
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.B malloc()
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all at the same time without interfering with how pools work.
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.P
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.B pool_create()
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Creates an allocation pool for subsequent calls to the pool
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allocation functions.
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When an extent is created for allocations it will be
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.I size
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bytes.
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Allocations from the pool have their sizes rounded up to a
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multiple of
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.I quantum
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bytes in length.
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Specifying
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.B 0
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for
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.I quantum
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will produce a quantum that should meet maximal alignment
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on most platforms.
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Unless
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.B POOL_NO_QALIGN
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is set in the
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.IR flags ,
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allocations will be aligned to addresses that are a
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multiple of
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.IR quantum .
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A
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.B NULL
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may be specified for the
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.I bomb
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function pointer if it is not needed. (See the
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.B pool_alloc()
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function for how it is used.)
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If
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.B POOL_CLEAR
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is set in the
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.IR flags ,
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all allocations from the pool will be initialized to zeros.
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If either
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.B POOL_PREPEND
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or
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.B POOL_INTERN
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is specified in the
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.IR flags ,
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each extent's data structure will be allocated at the start of the
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.IR size -length
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buffer (rather than as a separate, non-pool allocation), with the
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former extending the
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.I size
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to hold the structure, and the latter subtracting the structure's
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length from the indicated
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.IR size .
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.P
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.B pool_destroy()
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destroys an allocation
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.I pool
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and frees all its associated memory.
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.P
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.B pool_alloc()
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allocates
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.I size
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bytes from the specified
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.IR pool .
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If
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.I size
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is
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.BR 0 ,
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.I quantum
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bytes will be allocated.
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If the pool has been created without
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.BR POOL_NO_QALIGN ,
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every chunk of memory that is returned will be suitably aligned.
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You can use this with the default
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.I quantum
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size to ensure that all memory can store a variable of any type.
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If the requested memory cannot be allocated, the
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.I bomb()
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function will be called with
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.I msg
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as its sole argument (if the function was defined at the time
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the pool was created), and then a
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.B NULL
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address is returned (assuming that the bomb function didn't exit).
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.P
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.B pool_free()
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frees
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.I size
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bytes pointed to by an
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.I addr
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that was previously allocated in the specified
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.IR pool .
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If
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.I size
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is
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.BR 0 ,
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.I quantum
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bytes will be freed.
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The memory freed within an extent will not be reusable until
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all of the memory in that extent has been freed with one
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exception: the most recent pool allocation may be freed back
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into the pool prior to making any further allocations.
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If enough free calls are made to indicate that an extent has no
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remaining allocated objects (as computed by the total freed size for
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an extent), its memory will be completely freed back to the system.
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If
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.I addr
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is
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.BR NULL ,
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no memory will be freed, but subsequent allocations will come
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from a new extent.
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.P
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.B pool_free_old()
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takes a boundary
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.I addr
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value that was returned by
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.B pool_boundary()
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and frees up any extents in the
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.I pool
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that have data allocated from that point backward in time.
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NOTE: you must NOT mix calls to both
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.B pool_free
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and
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.B pool_free_old
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on the same pool!
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.P
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.B pool_boundary()
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asks for a boundary value that can be sent to
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.B pool_free_old()
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at a later time to free up all memory allocated prior to a particular
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moment in time.
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If the extent that holds the boundary point has allocations from after the
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boundary point, it will not be freed until a future
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.B pool_free_old()
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call encompasses the entirety of the extent's data.
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If
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.I len
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is non-zero, the call will also check if the active extent has at least
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that much free memory available in it, and if not, it will mark the
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extent as inactive, forcing a new extent to be used for future allocations.
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(You can specify -1 for
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.I len
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if you want to force a new extent to start.)
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.P
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.B pool_talloc()
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is a macro that takes a
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.I type
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and a
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.I count
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instead of a
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.IR size .
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It casts the return value to the correct pointer type.
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.P
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.B pool_tfree
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is a macro that calls
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.B pool_free
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on memory that was allocated by
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.BR pool_talloc() .
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.SH RETURN VALUE
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.B pool_create()
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returns a pointer to
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.BR "struct alloc_pool" .
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.P
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.B pool_alloc()
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and
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.B pool_talloc()
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return pointers to the allocated memory,
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or NULL if the request fails.
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The return type of
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.B pool_alloc()
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will normally require casting to the desired type but
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.B pool_talloc()
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will returns a pointer of the requested
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.IR type .
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.P
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.B pool_boundary()
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returns a pointer that should only be used in a call to
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.BR pool_free_old() .
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.P
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.BR pool_free() ,
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.BR pool_free_old() ,
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.B pool_tfree()
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and
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.B pool_destroy()
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return no value.
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.SH SEE ALSO
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.nf
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malloc(3)
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.SH AUTHOR
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pool_alloc was created by J.W. Schultz of Pegasystems Technologies.
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.SH BUGS AND ISSUES
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