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'\" t
.\" Copyright (c) 2012 by Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH malloc_get_state 3 2024-05-02 "Linux man-pages (unreleased)"
.SH NAME
malloc_get_state, malloc_set_state \-
record and restore state of malloc implementation
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <malloc.h>
.P
.B void *malloc_get_state(void);
.BI "int malloc_set_state(void *" state );
.fi
.SH DESCRIPTION
.IR Note :
these functions are removed in glibc 2.25.
.P
The
.BR malloc_get_state ()
function records the current state of all
.BR malloc (3)
internal bookkeeping variables
(but not the actual contents of the heap
or the state of
.BR malloc_hook (3)
functions pointers).
The state is recorded in a system-dependent opaque data structure
dynamically allocated via
.BR malloc (3),
and a pointer to that data structure is returned as the function result.
(It is the caller's responsibility to
.BR free (3)
this memory.)
.P
The
.BR malloc_set_state ()
function restores the state of all
.BR malloc (3)
internal bookkeeping variables to the values recorded in
the opaque data structure pointed to by
.IR state .
.SH RETURN VALUE
On success,
.BR malloc_get_state ()
returns a pointer to a newly allocated opaque data structure.
On error (for example, memory could not be allocated for the data structure),
.BR malloc_get_state ()
returns NULL.
.P
On success,
.BR malloc_set_state ()
returns 0.
If the implementation detects that
.I state
does not point to a correctly formed data structure,
.\" if(ms->magic != MALLOC_STATE_MAGIC) return -1;
.BR malloc_set_state ()
returns \-1.
If the implementation detects that
the version of the data structure referred to by
.I state
is a more recent version than this implementation knows about,
.\" /* Must fail if the major version is too high. */
.\" if((ms->version & ~0xffl) > (MALLOC_STATE_VERSION & ~0xffl)) return -2;
.BR malloc_set_state ()
returns \-2.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.na
.nh
.BR malloc_get_state (),
.BR malloc_set_state ()
T} Thread safety MT-Safe
.TE
.SH STANDARDS
GNU.
.SH NOTES
These functions are useful when using this
.BR malloc (3)
implementation as part of a shared library,
and the heap contents are saved/restored via some other method.
This technique is used by GNU Emacs to implement its "dumping" function.
.P
Hook function pointers are never saved or restored by these
functions, with two exceptions:
if malloc checking (see
.BR mallopt (3))
was in use when
.BR malloc_get_state ()
was called, then
.BR malloc_set_state ()
resets malloc checking hooks
.\" i.e., calls __malloc_check_init()
if possible;
.\" i.e., malloc checking is not already in use
.\" and the caller requested malloc checking
if malloc checking was not in use in the recorded state,
but the caller has requested malloc checking,
then the hooks are reset to 0.
.SH SEE ALSO
.BR malloc (3),
.BR mallopt (3)
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