/*------------------------------------------------------------------------- * * mcxt.c * POSTGRES memory context management code. * * This module handles context management operations that are independent * of the particular kind of context being operated on. It calls * context-type-specific operations via the function pointers in a * context's MemoryContextMethods struct. * * * Portions Copyright (c) 1996-2011, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * src/backend/utils/mmgr/mcxt.c * *------------------------------------------------------------------------- */ #include "postgres.h" #include "utils/memutils.h" /***************************************************************************** * GLOBAL MEMORY * *****************************************************************************/ /* * CurrentMemoryContext * Default memory context for allocations. */ MemoryContext CurrentMemoryContext = NULL; /* * Standard top-level contexts. For a description of the purpose of each * of these contexts, refer to src/backend/utils/mmgr/README */ MemoryContext TopMemoryContext = NULL; MemoryContext ErrorContext = NULL; MemoryContext PostmasterContext = NULL; MemoryContext CacheMemoryContext = NULL; MemoryContext MessageContext = NULL; MemoryContext TopTransactionContext = NULL; MemoryContext CurTransactionContext = NULL; /* This is a transient link to the active portal's memory context: */ MemoryContext PortalContext = NULL; static void MemoryContextStatsInternal(MemoryContext context, int level); /***************************************************************************** * EXPORTED ROUTINES * *****************************************************************************/ /* * MemoryContextInit * Start up the memory-context subsystem. * * This must be called before creating contexts or allocating memory in * contexts. TopMemoryContext and ErrorContext are initialized here; * other contexts must be created afterwards. * * In normal multi-backend operation, this is called once during * postmaster startup, and not at all by individual backend startup * (since the backends inherit an already-initialized context subsystem * by virtue of being forked off the postmaster). * * In a standalone backend this must be called during backend startup. */ void MemoryContextInit(void) { AssertState(TopMemoryContext == NULL); /* * Initialize TopMemoryContext as an AllocSetContext with slow growth rate * --- we don't really expect much to be allocated in it. * * (There is special-case code in MemoryContextCreate() for this call.) */ TopMemoryContext = AllocSetContextCreate((MemoryContext) NULL, "TopMemoryContext", 0, 8 * 1024, 8 * 1024); /* * Not having any other place to point CurrentMemoryContext, make it point * to TopMemoryContext. Caller should change this soon! */ CurrentMemoryContext = TopMemoryContext; /* * Initialize ErrorContext as an AllocSetContext with slow growth rate --- * we don't really expect much to be allocated in it. More to the point, * require it to contain at least 8K at all times. This is the only case * where retained memory in a context is *essential* --- we want to be * sure ErrorContext still has some memory even if we've run out * elsewhere! */ ErrorContext = AllocSetContextCreate(TopMemoryContext, "ErrorContext", 8 * 1024, 8 * 1024, 8 * 1024); } /* * MemoryContextReset * Release all space allocated within a context and its descendants, * but don't delete the contexts themselves. * * The type-specific reset routine handles the context itself, but we * have to do the recursion for the children. */ void MemoryContextReset(MemoryContext context) { AssertArg(MemoryContextIsValid(context)); /* save a function call in common case where there are no children */ if (context->firstchild != NULL) MemoryContextResetChildren(context); /* Nothing to do if no pallocs since startup or last reset */ if (!context->isReset) { (*context->methods->reset) (context); context->isReset = true; } } /* * MemoryContextResetChildren * Release all space allocated within a context's descendants, * but don't delete the contexts themselves. The named context * itself is not touched. */ void MemoryContextResetChildren(MemoryContext context) { MemoryContext child; AssertArg(MemoryContextIsValid(context)); for (child = context->firstchild; child != NULL; child = child->nextchild) MemoryContextReset(child); } /* * MemoryContextDelete * Delete a context and its descendants, and release all space * allocated therein. * * The type-specific delete routine removes all subsidiary storage * for the context, but we have to delete the context node itself, * as well as recurse to get the children. We must also delink the * node from its parent, if it has one. */ void MemoryContextDelete(MemoryContext context) { AssertArg(MemoryContextIsValid(context)); /* We had better not be deleting TopMemoryContext ... */ Assert(context != TopMemoryContext); /* And not CurrentMemoryContext, either */ Assert(context != CurrentMemoryContext); MemoryContextDeleteChildren(context); /* * We delink the context from its parent before deleting it, so that if * there's an error we won't have deleted/busted contexts still attached * to the context tree. Better a leak than a crash. */ MemoryContextSetParent(context, NULL); (*context->methods->delete_context) (context); pfree(context); } /* * MemoryContextDeleteChildren * Delete all the descendants of the named context and release all * space allocated therein. The named context itself is not touched. */ void MemoryContextDeleteChildren(MemoryContext context) { AssertArg(MemoryContextIsValid(context)); /* * MemoryContextDelete will delink the child from me, so just iterate as * long as there is a child. */ while (context->firstchild != NULL) MemoryContextDelete(context->firstchild); } /* * MemoryContextResetAndDeleteChildren * Release all space allocated within a context and delete all * its descendants. * * This is a common combination case where we want to preserve the * specific context but get rid of absolutely everything under it. */ void MemoryContextResetAndDeleteChildren(MemoryContext context) { AssertArg(MemoryContextIsValid(context)); MemoryContextDeleteChildren(context); MemoryContextReset(context); } /* * MemoryContextSetParent * Change a context to belong to a new parent (or no parent). * * We provide this as an API function because it is sometimes useful to * change a context's lifespan after creation. For example, a context * might be created underneath a transient context, filled with data, * and then reparented underneath CacheMemoryContext to make it long-lived. * In this way no special effort is needed to get rid of the context in case * a failure occurs before its contents are completely set up. * * Callers often assume that this function cannot fail, so don't put any * elog(ERROR) calls in it. * * A possible caller error is to reparent a context under itself, creating * a loop in the context graph. We assert here that context != new_parent, * but checking for multi-level loops seems more trouble than it's worth. */ void MemoryContextSetParent(MemoryContext context, MemoryContext new_parent) { AssertArg(MemoryContextIsValid(context)); AssertArg(context != new_parent); /* Delink from existing parent, if any */ if (context->parent) { MemoryContext parent = context->parent; if (context == parent->firstchild) parent->firstchild = context->nextchild; else { MemoryContext child; for (child = parent->firstchild; child; child = child->nextchild) { if (context == child->nextchild) { child->nextchild = context->nextchild; break; } } } } /* And relink */ if (new_parent) { AssertArg(MemoryContextIsValid(new_parent)); context->parent = new_parent; context->nextchild = new_parent->firstchild; new_parent->firstchild = context; } else { context->parent = NULL; context->nextchild = NULL; } } /* * GetMemoryChunkSpace * Given a currently-allocated chunk, determine the total space * it occupies (including all memory-allocation overhead). * * This is useful for measuring the total space occupied by a set of * allocated chunks. */ Size GetMemoryChunkSpace(void *pointer) { StandardChunkHeader *header; /* * Try to detect bogus pointers handed to us, poorly though we can. * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an * allocated chunk. */ Assert(pointer != NULL); Assert(pointer == (void *) MAXALIGN(pointer)); /* * OK, it's probably safe to look at the chunk header. */ header = (StandardChunkHeader *) ((char *) pointer - STANDARDCHUNKHEADERSIZE); AssertArg(MemoryContextIsValid(header->context)); return (*header->context->methods->get_chunk_space) (header->context, pointer); } /* * GetMemoryChunkContext * Given a currently-allocated chunk, determine the context * it belongs to. */ MemoryContext GetMemoryChunkContext(void *pointer) { StandardChunkHeader *header; /* * Try to detect bogus pointers handed to us, poorly though we can. * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an * allocated chunk. */ Assert(pointer != NULL); Assert(pointer == (void *) MAXALIGN(pointer)); /* * OK, it's probably safe to look at the chunk header. */ header = (StandardChunkHeader *) ((char *) pointer - STANDARDCHUNKHEADERSIZE); AssertArg(MemoryContextIsValid(header->context)); return header->context; } /* * MemoryContextIsEmpty * Is a memory context empty of any allocated space? */ bool MemoryContextIsEmpty(MemoryContext context) { AssertArg(MemoryContextIsValid(context)); /* * For now, we consider a memory context nonempty if it has any children; * perhaps this should be changed later. */ if (context->firstchild != NULL) return false; /* Otherwise use the type-specific inquiry */ return (*context->methods->is_empty) (context); } /* * MemoryContextStats * Print statistics about the named context and all its descendants. * * This is just a debugging utility, so it's not fancy. The statistics * are merely sent to stderr. */ void MemoryContextStats(MemoryContext context) { MemoryContextStatsInternal(context, 0); } static void MemoryContextStatsInternal(MemoryContext context, int level) { MemoryContext child; AssertArg(MemoryContextIsValid(context)); (*context->methods->stats) (context, level); for (child = context->firstchild; child != NULL; child = child->nextchild) MemoryContextStatsInternal(child, level + 1); } /* * MemoryContextCheck * Check all chunks in the named context. * * This is just a debugging utility, so it's not fancy. */ #ifdef MEMORY_CONTEXT_CHECKING void MemoryContextCheck(MemoryContext context) { MemoryContext child; AssertArg(MemoryContextIsValid(context)); (*context->methods->check) (context); for (child = context->firstchild; child != NULL; child = child->nextchild) MemoryContextCheck(child); } #endif /* * MemoryContextContains * Detect whether an allocated chunk of memory belongs to a given * context or not. * * Caution: this test is reliable as long as 'pointer' does point to * a chunk of memory allocated from *some* context. If 'pointer' points * at memory obtained in some other way, there is a small chance of a * false-positive result, since the bits right before it might look like * a valid chunk header by chance. */ bool MemoryContextContains(MemoryContext context, void *pointer) { StandardChunkHeader *header; /* * Try to detect bogus pointers handed to us, poorly though we can. * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an * allocated chunk. */ if (pointer == NULL || pointer != (void *) MAXALIGN(pointer)) return false; /* * OK, it's probably safe to look at the chunk header. */ header = (StandardChunkHeader *) ((char *) pointer - STANDARDCHUNKHEADERSIZE); /* * If the context link doesn't match then we certainly have a non-member * chunk. Also check for a reasonable-looking size as extra guard against * being fooled by bogus pointers. */ if (header->context == context && AllocSizeIsValid(header->size)) return true; return false; } /*-------------------- * MemoryContextCreate * Context-type-independent part of context creation. * * This is only intended to be called by context-type-specific * context creation routines, not by the unwashed masses. * * The context creation procedure is a little bit tricky because * we want to be sure that we don't leave the context tree invalid * in case of failure (such as insufficient memory to allocate the * context node itself). The procedure goes like this: * 1. Context-type-specific routine first calls MemoryContextCreate(), * passing the appropriate tag/size/methods values (the methods * pointer will ordinarily point to statically allocated data). * The parent and name parameters usually come from the caller. * 2. MemoryContextCreate() attempts to allocate the context node, * plus space for the name. If this fails we can ereport() with no * damage done. * 3. We fill in all of the type-independent MemoryContext fields. * 4. We call the type-specific init routine (using the methods pointer). * The init routine is required to make the node minimally valid * with zero chance of failure --- it can't allocate more memory, * for example. * 5. Now we have a minimally valid node that can behave correctly * when told to reset or delete itself. We link the node to its * parent (if any), making the node part of the context tree. * 6. We return to the context-type-specific routine, which finishes * up type-specific initialization. This routine can now do things * that might fail (like allocate more memory), so long as it's * sure the node is left in a state that delete will handle. * * This protocol doesn't prevent us from leaking memory if step 6 fails * during creation of a top-level context, since there's no parent link * in that case. However, if you run out of memory while you're building * a top-level context, you might as well go home anyway... * * Normally, the context node and the name are allocated from * TopMemoryContext (NOT from the parent context, since the node must * survive resets of its parent context!). However, this routine is itself * used to create TopMemoryContext! If we see that TopMemoryContext is NULL, * we assume we are creating TopMemoryContext and use malloc() to allocate * the node. * * Note that the name field of a MemoryContext does not point to * separately-allocated storage, so it should not be freed at context * deletion. *-------------------- */ MemoryContext MemoryContextCreate(NodeTag tag, Size size, MemoryContextMethods *methods, MemoryContext parent, const char *name) { MemoryContext node; Size needed = size + strlen(name) + 1; /* Get space for node and name */ if (TopMemoryContext != NULL) { /* Normal case: allocate the node in TopMemoryContext */ node = (MemoryContext) MemoryContextAlloc(TopMemoryContext, needed); } else { /* Special case for startup: use good ol' malloc */ node = (MemoryContext) malloc(needed); Assert(node != NULL); } /* Initialize the node as best we can */ MemSet(node, 0, size); node->type = tag; node->methods = methods; node->parent = NULL; /* for the moment */ node->firstchild = NULL; node->nextchild = NULL; node->isReset = true; node->name = ((char *) node) + size; strcpy(node->name, name); /* Type-specific routine finishes any other essential initialization */ (*node->methods->init) (node); /* OK to link node to parent (if any) */ /* Could use MemoryContextSetParent here, but doesn't seem worthwhile */ if (parent) { node->parent = parent; node->nextchild = parent->firstchild; parent->firstchild = node; } /* Return to type-specific creation routine to finish up */ return node; } /* * MemoryContextAlloc * Allocate space within the specified context. * * This could be turned into a macro, but we'd have to import * nodes/memnodes.h into postgres.h which seems a bad idea. */ void * MemoryContextAlloc(MemoryContext context, Size size) { AssertArg(MemoryContextIsValid(context)); if (!AllocSizeIsValid(size)) elog(ERROR, "invalid memory alloc request size %lu", (unsigned long) size); context->isReset = false; return (*context->methods->alloc) (context, size); } /* * MemoryContextAllocZero * Like MemoryContextAlloc, but clears allocated memory * * We could just call MemoryContextAlloc then clear the memory, but this * is a very common combination, so we provide the combined operation. */ void * MemoryContextAllocZero(MemoryContext context, Size size) { void *ret; AssertArg(MemoryContextIsValid(context)); if (!AllocSizeIsValid(size)) elog(ERROR, "invalid memory alloc request size %lu", (unsigned long) size); context->isReset = false; ret = (*context->methods->alloc) (context, size); MemSetAligned(ret, 0, size); return ret; } /* * MemoryContextAllocZeroAligned * MemoryContextAllocZero where length is suitable for MemSetLoop * * This might seem overly specialized, but it's not because newNode() * is so often called with compile-time-constant sizes. */ void * MemoryContextAllocZeroAligned(MemoryContext context, Size size) { void *ret; AssertArg(MemoryContextIsValid(context)); if (!AllocSizeIsValid(size)) elog(ERROR, "invalid memory alloc request size %lu", (unsigned long) size); context->isReset = false; ret = (*context->methods->alloc) (context, size); MemSetLoop(ret, 0, size); return ret; } /* * pfree * Release an allocated chunk. */ void pfree(void *pointer) { StandardChunkHeader *header; /* * Try to detect bogus pointers handed to us, poorly though we can. * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an * allocated chunk. */ Assert(pointer != NULL); Assert(pointer == (void *) MAXALIGN(pointer)); /* * OK, it's probably safe to look at the chunk header. */ header = (StandardChunkHeader *) ((char *) pointer - STANDARDCHUNKHEADERSIZE); AssertArg(MemoryContextIsValid(header->context)); (*header->context->methods->free_p) (header->context, pointer); } /* * repalloc * Adjust the size of a previously allocated chunk. */ void * repalloc(void *pointer, Size size) { StandardChunkHeader *header; /* * Try to detect bogus pointers handed to us, poorly though we can. * Presumably, a pointer that isn't MAXALIGNED isn't pointing at an * allocated chunk. */ Assert(pointer != NULL); Assert(pointer == (void *) MAXALIGN(pointer)); /* * OK, it's probably safe to look at the chunk header. */ header = (StandardChunkHeader *) ((char *) pointer - STANDARDCHUNKHEADERSIZE); AssertArg(MemoryContextIsValid(header->context)); if (!AllocSizeIsValid(size)) elog(ERROR, "invalid memory alloc request size %lu", (unsigned long) size); /* isReset must be false already */ Assert(!header->context->isReset); return (*header->context->methods->realloc) (header->context, pointer, size); } /* * MemoryContextSwitchTo * Returns the current context; installs the given context. * * palloc.h defines an inline version of this function if allowed by the * compiler; in which case the definition below is skipped. */ #ifndef USE_INLINE MemoryContext MemoryContextSwitchTo(MemoryContext context) { MemoryContext old; AssertArg(MemoryContextIsValid(context)); old = CurrentMemoryContext; CurrentMemoryContext = context; return old; } #endif /* ! USE_INLINE */ /* * MemoryContextStrdup * Like strdup(), but allocate from the specified context */ char * MemoryContextStrdup(MemoryContext context, const char *string) { char *nstr; Size len = strlen(string) + 1; nstr = (char *) MemoryContextAlloc(context, len); memcpy(nstr, string, len); return nstr; } /* * pnstrdup * Like pstrdup(), but append null byte to a * not-necessarily-null-terminated input string. */ char * pnstrdup(const char *in, Size len) { char *out = palloc(len + 1); memcpy(out, in, len); out[len] = '\0'; return out; } #if defined(WIN32) || defined(__CYGWIN__) /* * Memory support routines for libpgport on Win32 * * Win32 can't load a library that PGDLLIMPORTs a variable * if the link object files also PGDLLIMPORT the same variable. * For this reason, libpgport can't reference CurrentMemoryContext * in the palloc macro calls. * * To fix this, we create several functions here that allow us to * manage memory without doing the inline in libpgport. */ void * pgport_palloc(Size sz) { return palloc(sz); } char * pgport_pstrdup(const char *str) { return pstrdup(str); } /* Doesn't reference a PGDLLIMPORT variable, but here for completeness. */ void pgport_pfree(void *pointer) { pfree(pointer); } #endif