PostgreSQL Source Code  git master
 All Data Structures Namespaces Files Functions Variables Typedefs Enumerations Enumerator Macros
palloc.h
Go to the documentation of this file.
1 /*-------------------------------------------------------------------------
2  *
3  * palloc.h
4  * POSTGRES memory allocator definitions.
5  *
6  * This file contains the basic memory allocation interface that is
7  * needed by almost every backend module. It is included directly by
8  * postgres.h, so the definitions here are automatically available
9  * everywhere. Keep it lean!
10  *
11  * Memory allocation occurs within "contexts". Every chunk obtained from
12  * palloc()/MemoryContextAlloc() is allocated within a specific context.
13  * The entire contents of a context can be freed easily and quickly by
14  * resetting or deleting the context --- this is both faster and less
15  * prone to memory-leakage bugs than releasing chunks individually.
16  * We organize contexts into context trees to allow fine-grain control
17  * over chunk lifetime while preserving the certainty that we will free
18  * everything that should be freed. See utils/mmgr/README for more info.
19  *
20  *
21  * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
22  * Portions Copyright (c) 1994, Regents of the University of California
23  *
24  * src/include/utils/palloc.h
25  *
26  *-------------------------------------------------------------------------
27  */
28 #ifndef PALLOC_H
29 #define PALLOC_H
30 
31 /*
32  * Type MemoryContextData is declared in nodes/memnodes.h. Most users
33  * of memory allocation should just treat it as an abstract type, so we
34  * do not provide the struct contents here.
35  */
37 
38 /*
39  * A memory context can have callback functions registered on it. Any such
40  * function will be called once just before the context is next reset or
41  * deleted. The MemoryContextCallback struct describing such a callback
42  * typically would be allocated within the context itself, thereby avoiding
43  * any need to manage it explicitly (the reset/delete action will free it).
44  */
45 typedef void (*MemoryContextCallbackFunction) (void *arg);
46 
47 typedef struct MemoryContextCallback
48 {
49  MemoryContextCallbackFunction func; /* function to call */
50  void *arg; /* argument to pass it */
51  struct MemoryContextCallback *next; /* next in list of callbacks */
53 
54 /*
55  * CurrentMemoryContext is the default allocation context for palloc().
56  * Avoid accessing it directly! Instead, use MemoryContextSwitchTo()
57  * to change the setting.
58  */
59 extern PGDLLIMPORT MemoryContext CurrentMemoryContext;
60 
61 /*
62  * Flags for MemoryContextAllocExtended.
63  */
64 #define MCXT_ALLOC_HUGE 0x01 /* allow huge allocation (> 1 GB) */
65 #define MCXT_ALLOC_NO_OOM 0x02 /* no failure if out-of-memory */
66 #define MCXT_ALLOC_ZERO 0x04 /* zero allocated memory */
67 
68 /*
69  * Fundamental memory-allocation operations (more are in utils/memutils.h)
70  */
71 extern void *MemoryContextAlloc(MemoryContext context, Size size);
72 extern void *MemoryContextAllocZero(MemoryContext context, Size size);
73 extern void *MemoryContextAllocZeroAligned(MemoryContext context, Size size);
74 extern void *MemoryContextAllocExtended(MemoryContext context,
75  Size size, int flags);
76 
77 extern void *palloc(Size size);
78 extern void *palloc0(Size size);
79 extern void *palloc_extended(Size size, int flags);
80 extern void *repalloc(void *pointer, Size size);
81 extern void pfree(void *pointer);
82 
83 /*
84  * The result of palloc() is always word-aligned, so we can skip testing
85  * alignment of the pointer when deciding which MemSet variant to use.
86  * Note that this variant does not offer any advantage, and should not be
87  * used, unless its "sz" argument is a compile-time constant; therefore, the
88  * issue that it evaluates the argument multiple times isn't a problem in
89  * practice.
90  */
91 #define palloc0fast(sz) \
92  ( MemSetTest(0, sz) ? \
93  MemoryContextAllocZeroAligned(CurrentMemoryContext, sz) : \
94  MemoryContextAllocZero(CurrentMemoryContext, sz) )
95 
96 /* Higher-limit allocators. */
97 extern void *MemoryContextAllocHuge(MemoryContext context, Size size);
98 extern void *repalloc_huge(void *pointer, Size size);
99 
100 /*
101  * Although this header file is nominally backend-only, certain frontend
102  * programs like pg_controldata include it via postgres.h. For some compilers
103  * it's necessary to hide the inline definition of MemoryContextSwitchTo in
104  * this scenario; hence the #ifndef FRONTEND.
105  */
106 
107 #ifndef FRONTEND
108 static inline MemoryContext
109 MemoryContextSwitchTo(MemoryContext context)
110 {
111  MemoryContext old = CurrentMemoryContext;
112 
113  CurrentMemoryContext = context;
114  return old;
115 }
116 #endif /* FRONTEND */
117 
118 /* Registration of memory context reset/delete callbacks */
119 extern void MemoryContextRegisterResetCallback(MemoryContext context,
121 
122 /*
123  * These are like standard strdup() except the copied string is
124  * allocated in a context, not with malloc().
125  */
126 extern char *MemoryContextStrdup(MemoryContext context, const char *string);
127 extern char *pstrdup(const char *in);
128 extern char *pnstrdup(const char *in, Size len);
129 
130 extern char *pchomp(const char *in);
131 
132 /* sprintf into a palloc'd buffer --- these are in psprintf.c */
133 extern char *psprintf(const char *fmt,...) pg_attribute_printf(1, 2);
134 extern size_t pvsnprintf(char *buf, size_t len, const char *fmt, va_list args) pg_attribute_printf(3, 0);
135 
136 #endif /* PALLOC_H */
MemoryContextCallbackFunction func
Definition: palloc.h:49
void * MemoryContextAllocZeroAligned(MemoryContext context, Size size)
Definition: mcxt.c:779
void * MemoryContextAllocHuge(MemoryContext context, Size size)
Definition: mcxt.c:998
char * pstrdup(const char *in)
Definition: mcxt.c:1077
static MemoryContext MemoryContextSwitchTo(MemoryContext context)
Definition: palloc.h:109
void * repalloc_huge(void *pointer, Size size)
Definition: mcxt.c:1031
char * MemoryContextStrdup(MemoryContext context, const char *string)
Definition: mcxt.c:1064
void * palloc_extended(Size size, int flags)
Definition: mcxt.c:909
void * MemoryContextAlloc(MemoryContext context, Size size)
Definition: mcxt.c:707
#define PGDLLIMPORT
Definition: c.h:1063
#define pg_attribute_printf(f, a)
Definition: c.h:638
char size_t pvsnprintf(char *buf, size_t len, const char *fmt, va_list args) pg_attribute_printf(3
static char * buf
Definition: pg_test_fsync.c:66
void * MemoryContextAllocExtended(MemoryContext context, Size size, int flags)
Definition: mcxt.c:813
PGDLLIMPORT MemoryContext CurrentMemoryContext
Definition: mcxt.c:37
void * palloc(Size size)
Definition: mcxt.c:849
char * pnstrdup(const char *in, Size len)
Definition: mcxt.c:1088
struct MemoryContextCallback MemoryContextCallback
void(* MemoryContextCallbackFunction)(void *arg)
Definition: palloc.h:45
struct MemoryContextData * MemoryContext
Definition: palloc.h:36
void pfree(void *pointer)
Definition: mcxt.c:950
void MemoryContextRegisterResetCallback(MemoryContext context, MemoryContextCallback *cb)
Definition: mcxt.c:265
char * psprintf(const char *fmt,...) pg_attribute_printf(1
size_t Size
Definition: c.h:356
void * MemoryContextAllocZero(MemoryContext context, Size size)
Definition: mcxt.c:742
char * pchomp(const char *in)
Definition: mcxt.c:1101
void * repalloc(void *pointer, Size size)
Definition: mcxt.c:963
struct MemoryContextCallback * next
Definition: palloc.h:51
void * arg
void * palloc0(Size size)
Definition: mcxt.c:878