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db_include/utils/palloc.h

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+/*-------------------------------------------------------------------------
+ *
+ * palloc.h
+ *	  POSTGRES memory allocator definitions.
+ *
+ * This file contains the basic memory allocation interface that is
+ * needed by almost every backend module.  It is included directly by
+ * postgres.h, so the definitions here are automatically available
+ * everywhere.  Keep it lean!
+ *
+ * Memory allocation occurs within "contexts".  Every chunk obtained from
+ * palloc()/MemoryContextAlloc() is allocated within a specific context.
+ * The entire contents of a context can be freed easily and quickly by
+ * resetting or deleting the context --- this is both faster and less
+ * prone to memory-leakage bugs than releasing chunks individually.
+ * We organize contexts into context trees to allow fine-grain control
+ * over chunk lifetime while preserving the certainty that we will free
+ * everything that should be freed.  See utils/mmgr/README for more info.
+ *
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/utils/palloc.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef PALLOC_H
+#define PALLOC_H
+
+/*
+ * Type MemoryContextData is declared in nodes/memnodes.h.  Most users
+ * of memory allocation should just treat it as an abstract type, so we
+ * do not provide the struct contents here.
+ */
+typedef struct MemoryContextData *MemoryContext;
+
+/*
+ * A memory context can have callback functions registered on it.  Any such
+ * function will be called once just before the context is next reset or
+ * deleted.  The MemoryContextCallback struct describing such a callback
+ * typically would be allocated within the context itself, thereby avoiding
+ * any need to manage it explicitly (the reset/delete action will free it).
+ */
+typedef void (*MemoryContextCallbackFunction) (void *arg);
+
+typedef struct MemoryContextCallback
+{
+	MemoryContextCallbackFunction func; /* function to call */
+	void	   *arg;			/* argument to pass it */
+	struct MemoryContextCallback *next; /* next in list of callbacks */
+} MemoryContextCallback;
+
+/*
+ * CurrentMemoryContext is the default allocation context for palloc().
+ * Avoid accessing it directly!  Instead, use MemoryContextSwitchTo()
+ * to change the setting.
+ */
+extern PGDLLIMPORT MemoryContext CurrentMemoryContext;
+
+/*
+ * Flags for MemoryContextAllocExtended.
+ */
+#define MCXT_ALLOC_HUGE			0x01	/* allow huge allocation (> 1 GB) */
+#define MCXT_ALLOC_NO_OOM		0x02	/* no failure if out-of-memory */
+#define MCXT_ALLOC_ZERO			0x04	/* zero allocated memory */
+
+/*
+ * Fundamental memory-allocation operations (more are in utils/memutils.h)
+ */
+extern void *MemoryContextAlloc(MemoryContext context, Size size);
+extern void *MemoryContextAllocZero(MemoryContext context, Size size);
+extern void *MemoryContextAllocZeroAligned(MemoryContext context, Size size);
+extern void *MemoryContextAllocExtended(MemoryContext context,
+										Size size, int flags);
+
+extern void *palloc(Size size);
+extern void *palloc0(Size size);
+extern void *palloc_extended(Size size, int flags);
+extern pg_nodiscard void *repalloc(void *pointer, Size size);
+extern void pfree(void *pointer);
+
+/*
+ * The result of palloc() is always word-aligned, so we can skip testing
+ * alignment of the pointer when deciding which MemSet variant to use.
+ * Note that this variant does not offer any advantage, and should not be
+ * used, unless its "sz" argument is a compile-time constant; therefore, the
+ * issue that it evaluates the argument multiple times isn't a problem in
+ * practice.
+ */
+#define palloc0fast(sz) \
+	( MemSetTest(0, sz) ? \
+		MemoryContextAllocZeroAligned(CurrentMemoryContext, sz) : \
+		MemoryContextAllocZero(CurrentMemoryContext, sz) )
+
+/* Higher-limit allocators. */
+extern void *MemoryContextAllocHuge(MemoryContext context, Size size);
+extern pg_nodiscard void *repalloc_huge(void *pointer, Size size);
+
+/*
+ * Although this header file is nominally backend-only, certain frontend
+ * programs like pg_controldata include it via postgres.h.  For some compilers
+ * it's necessary to hide the inline definition of MemoryContextSwitchTo in
+ * this scenario; hence the #ifndef FRONTEND.
+ */
+
+#ifndef FRONTEND
+static inline MemoryContext
+MemoryContextSwitchTo(MemoryContext context)
+{
+	MemoryContext old = CurrentMemoryContext;
+
+	CurrentMemoryContext = context;
+	return old;
+}
+#endif							/* FRONTEND */
+
+/* Registration of memory context reset/delete callbacks */
+extern void MemoryContextRegisterResetCallback(MemoryContext context,
+											   MemoryContextCallback *cb);
+
+/*
+ * These are like standard strdup() except the copied string is
+ * allocated in a context, not with malloc().
+ */
+extern char *MemoryContextStrdup(MemoryContext context, const char *string);
+extern char *pstrdup(const char *in);
+extern char *pnstrdup(const char *in, Size len);
+
+extern char *pchomp(const char *in);
+
+/* sprintf into a palloc'd buffer --- these are in psprintf.c */
+extern char *psprintf(const char *fmt,...) pg_attribute_printf(1, 2);
+extern size_t pvsnprintf(char *buf, size_t len, const char *fmt, va_list args) pg_attribute_printf(3, 0);
+
+#endif							/* PALLOC_H */