1PTHREAD_ATTR_GETGUARDSIZE(P)POSIX Programmer's ManuaPlTHREAD_ATTR_GETGUARDSIZE(P)
2
6 pthread_attr_getguardsize, pthread_attr_setguardsize - get and set the
7 thread guardsize attribute
8
10 #include <pthread.h>
11 int pthread_attr_getguardsize(const pthread_attr_t *restrict attr,
13 size_t *restrict guardsize);
14 int pthread_attr_setguardsize(pthread_attr_t *attr,
15 size_t guardsize);
16
19 The pthread_attr_getguardsize() function shall get the guardsize
20 attribute in the attr object. This attribute shall be returned in the
21 guardsize parameter.
22 The pthread_attr_setguardsize() function shall set the guardsize
24 attribute in the attr object. The new value of this attribute shall be
25 obtained from the guardsize parameter. If guardsize is zero, a guard
26 area shall not be provided for threads created with attr. If guardsize
27 is greater than zero, a guard area of at least size guardsize bytes
28 shall be provided for each thread created with attr.
29 The guardsize attribute controls the size of the guard area for the
31 created thread's stack. The guardsize attribute provides protection
32 against overflow of the stack pointer. If a thread's stack is created
33 with guard protection, the implementation allocates extra memory at the
34 overflow end of the stack as a buffer against stack overflow of the
35 stack pointer. If an application overflows into this buffer an error
36 shall result (possibly in a SIGSEGV signal being delivered to the
37 thread).
38 A conforming implementation may round up the value contained in guard‐
40 size to a multiple of the configurable system variable {PAGESIZE} (see
41 <sys/mman.h>). If an implementation rounds up the value of guardsize to
42 a multiple of {PAGESIZE}, a call to pthread_attr_getguardsize() speci‐
43 fying attr shall store in the guardsize parameter the guard size speci‐
44 fied by the previous pthread_attr_setguardsize() function call.
45 The default value of the guardsize attribute is {PAGESIZE} bytes. The
47 actual value of {PAGESIZE} is implementation-defined.
48 If the stackaddr or stack attribute has been set (that is, the caller
50 is allocating and managing its own thread stacks), the guardsize
51 attribute shall be ignored and no protection shall be provided by the
52 implementation. It is the responsibility of the application to manage
53 stack overflow along with stack allocation and management in this case.
54
56 If successful, the pthread_attr_getguardsize() and pthread_attr_set‐
57 guardsize() functions shall return zero; otherwise, an error number
58 shall be returned to indicate the error.
59
61 The pthread_attr_getguardsize() and pthread_attr_setguardsize() func‐
62 tions shall fail if:
63 EINVAL The attribute attr is invalid.
65 EINVAL The parameter guardsize is invalid.
67 These functions shall not return an error code of [EINTR].
70 The following sections are informative.
72
74 None.
75
77 None.
78
80 The guardsize attribute is provided to the application for two reasons:
81 1. Overflow protection can potentially result in wasted system
83 resources. An application that creates a large number of threads,
84 and which knows its threads never overflow their stack, can save
85 system resources by turning off guard areas.
86 2. When threads allocate large data structures on the stack, large
88 guard areas may be needed to detect stack overflow.
89
91 None.
92
94 The Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>,
95 <sys/mman.h>
96
98 Portions of this text are reprinted and reproduced in electronic form
99 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
100 -- Portable Operating System Interface (POSIX), The Open Group Base
101 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
102 Electrical and Electronics Engineers, Inc and The Open Group. In the
103 event of any discrepancy between this version and the original IEEE and
104 The Open Group Standard, the original IEEE and The Open Group Standard
105 is the referee document. The original Standard can be obtained online
106 at http://www.opengroup.org/unix/online.html .
107IEEE/The Open Group 2003 PTHREAD_ATTR_GETGUARDSIZE(P)