BSD 4_2 release

[unix-history] / usr / src / lib / libc / gen / malloc.c

diff --git a/usr/src/lib/libc/gen/malloc.c b/usr/src/lib/libc/gen/malloc.c
index dd9dd10..3d4f7c6 100644 (file)
--- a/usr/src/lib/libc/gen/malloc.c
+++ b/usr/src/lib/libc/gen/malloc.c
@@ -1,190 +1,329 @@
-/* @(#)malloc.c        4.1 (Berkeley) 12/21/80 */
+#ifndef lint
+static char sccsid[] = "@(#)malloc.c   4.3 (Berkeley) 9/16/83";
+#endif
+
+/*
+ * malloc.c (Caltech) 2/21/82
+ * Chris Kingsley, kingsley@cit-20.
+ *
+ * This is a very fast storage allocator.  It allocates blocks of a small 
+ * number of different sizes, and keeps free lists of each size.  Blocks that
+ * don't exactly fit are passed up to the next larger size.  In this 
+ * implementation, the available sizes are 2^n-4 (or 2^n-12) bytes long.
+ * This is designed for use in a program that uses vast quantities of memory,
+ * but bombs when it runs out. 
+ */
+
+#include <sys/types.h>
+
+#define        NULL 0
+
+/*
+ * The overhead on a block is at least 4 bytes.  When free, this space
+ * contains a pointer to the next free block, and the bottom two bits must
+ * be zero.  When in use, the first byte is set to MAGIC, and the second
+ * byte is the size index.  The remaining bytes are for alignment.
+ * If range checking is enabled and the size of the block fits
+ * in two bytes, then the top two bytes hold the size of the requested block
+ * plus the range checking words, and the header word MINUS ONE.
+ */
+union  overhead {
+       union   overhead *ov_next;      /* when free */
+       struct {
+               u_char  ovu_magic;      /* magic number */
+               u_char  ovu_index;      /* bucket # */
+#ifdef RCHECK
+               u_short ovu_size;       /* actual block size */
+               u_int   ovu_rmagic;     /* range magic number */
+#endif
+       } ovu;
+#define        ov_magic        ovu.ovu_magic
+#define        ov_index        ovu.ovu_index
+#define        ov_size         ovu.ovu_size
+#define        ov_rmagic       ovu.ovu_rmagic
+};
+
+#define        MAGIC           0xff            /* magic # on accounting info */
+#define RMAGIC         0x55555555      /* magic # on range info */
+#ifdef RCHECK
+#define        RSLOP           sizeof (u_int)
+#else
+#define        RSLOP           0
+#endif
+
+/*
+ * nextf[i] is the pointer to the next free block of size 2^(i+3).  The
+ * smallest allocatable block is 8 bytes.  The overhead information
+ * precedes the data area returned to the user.
+ */
+#define        NBUCKETS 30
+static union overhead *nextf[NBUCKETS];
+extern char *sbrk();
+
+#ifdef MSTATS
+/*
+ * nmalloc[i] is the difference between the number of mallocs and frees
+ * for a given block size.
+ */
+static u_int nmalloc[NBUCKETS];
+#include <stdio.h>
+#endif
+

 #ifdef debug
 #ifdef debug

-#define ASSERT(p) if(!(p))botch("p");else
+#define        ASSERT(p)   if (!(p)) botch("p"); else
+static

 botch(s)
 botch(s)

-char *s;
+       char *s;

 {
 {

-       printf("assertion botched: %s\n",s);
+
+       printf("assertion botched: %s\n", s);

        abort();
 }
 #else
        abort();
 }
 #else

-#define ASSERT(p)
+#define        ASSERT(p)

 #endif
 
 #endif
 

-/*     avoid break bug */
-#ifdef pdp11
-#define GRANULE 64
-#else
-#define GRANULE 0
-#endif
-/*     C storage allocator
- *     circular first-fit strategy
- *     works with noncontiguous, but monotonically linked, arena
- *     each block is preceded by a ptr to the (pointer of) 
- *     the next following block
- *     blocks are exact number of words long 
- *     aligned to the data type requirements of ALIGN
- *     pointers to blocks must have BUSY bit 0
- *     bit in ptr is 1 for busy, 0 for idle
- *     gaps in arena are merely noted as busy blocks
- *     last block of arena (pointed to by alloct) is empty and
- *     has a pointer to first
- *     idle blocks are coalesced during space search
- *
- *     a different implementation may need to redefine
- *     ALIGN, NALIGN, BLOCK, BUSY, INT
- *     where INT is integer type to which a pointer can be cast
-*/
-#define INT int
-#define ALIGN int
-#define NALIGN 1
-#define WORD sizeof(union store)
-#define BLOCK 1024     /* a multiple of WORD*/
-#define BUSY 1
-#define NULL 0
-#define testbusy(p) ((INT)(p)&BUSY)
-#define setbusy(p) (union store *)((INT)(p)|BUSY)
-#define clearbusy(p) (union store *)((INT)(p)&~BUSY)
-
-union store { union store *ptr;
-             ALIGN dummy[NALIGN];
-             int calloc;       /*calloc clears an array of integers*/
-};
-
-static union store allocs[2];  /*initial arena*/
-static union store *allocp;    /*search ptr*/
-static union store *alloct;    /*arena top*/
-static union store *allocx;    /*for benefit of realloc*/
-char   *sbrk();
-

 char *
 malloc(nbytes)
 char *
 malloc(nbytes)

-unsigned nbytes;
+       register unsigned nbytes;

 {
 {

-       register union store *p, *q;
-       register nw;
-       static temp;    /*coroutines assume no auto*/
-
-       if(allocs[0].ptr==0) {  /*first time*/
-               allocs[0].ptr = setbusy(&allocs[1]);
-               allocs[1].ptr = setbusy(&allocs[0]);
-               alloct = &allocs[1];
-               allocp = &allocs[0];
-       }
-       nw = (nbytes+WORD+WORD-1)/WORD;
-       ASSERT(allocp>=allocs && allocp<=alloct);
-       ASSERT(allock());
-       for(p=allocp; ; ) {
-               for(temp=0; ; ) {
-                       if(!testbusy(p->ptr)) {
-                               while(!testbusy((q=p->ptr)->ptr)) {
-                                       ASSERT(q>p&&q<alloct);
-                                       p->ptr = q->ptr;
-                               }
-                               if(q>=p+nw && p+nw>=p)
-                                       goto found;
-                       }
-                       q = p;
-                       p = clearbusy(p->ptr);
-                       if(p>q)
-                               ASSERT(p<=alloct);
-                       else if(q!=alloct || p!=allocs) {
-                               ASSERT(q==alloct&&p==allocs);
-                               return(NULL);
-                       } else if(++temp>1)
-                               break;
-               }
-               temp = ((nw+BLOCK/WORD)/(BLOCK/WORD))*(BLOCK/WORD);
-               q = (union store *)sbrk(0);
-               if(q+temp+GRANULE < q) {
-                       return(NULL);
-               }
-               q = (union store *)sbrk(temp*WORD);
-               if((INT)q == -1) {
-                       return(NULL);
-               }
-               ASSERT(q>alloct);
-               alloct->ptr = q;
-               if(q!=alloct+1)
-                       alloct->ptr = setbusy(alloct->ptr);
-               alloct = q->ptr = q+temp-1;
-               alloct->ptr = setbusy(allocs);
-       }
-found:
-       allocp = p + nw;
-       ASSERT(allocp<=alloct);
-       if(q>allocp) {
-               allocx = allocp->ptr;
-               allocp->ptr = p->ptr;
-       }
-       p->ptr = setbusy(allocp);
-       return((char *)(p+1));
+       register union overhead *p;
+       register int bucket = 0;
+       register unsigned shiftr;
+
+       /*
+        * Convert amount of memory requested into
+        * closest block size stored in hash buckets
+        * which satisfies request.  Account for
+        * space used per block for accounting.
+        */
+       nbytes += sizeof (union overhead) + RSLOP;
+       nbytes = (nbytes + 3) &~ 3; 
+       shiftr = (nbytes - 1) >> 2;
+       /* apart from this loop, this is O(1) */
+       while (shiftr >>= 1)
+               bucket++;
+       /*
+        * If nothing in hash bucket right now,
+        * request more memory from the system.
+        */
+       if (nextf[bucket] == NULL)    
+               morecore(bucket);
+       if ((p = (union overhead *)nextf[bucket]) == NULL)
+               return (NULL);
+       /* remove from linked list */
+       nextf[bucket] = nextf[bucket]->ov_next;
+       p->ov_magic = MAGIC;
+       p->ov_index= bucket;
+#ifdef MSTATS
+       nmalloc[bucket]++;
+#endif
+#ifdef RCHECK
+       /*
+        * Record allocated size of block and
+        * bound space with magic numbers.
+        */
+       if (nbytes <= 0x10000)
+               p->ov_size = nbytes - 1;
+       p->ov_rmagic = RMAGIC;
+       *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC;
+#endif
+       return ((char *)(p + 1));

 }
 
 }
 

-/*     freeing strategy tuned for LIFO allocation
-*/
-free(ap)
-register char *ap;
+/*
+ * Allocate more memory to the indicated bucket.
+ */
+static
+morecore(bucket)
+       register bucket;

 {
 {

-       register union store *p = (union store *)ap;
-
-       ASSERT(p>clearbusy(allocs[1].ptr)&&p<=alloct);
-       ASSERT(allock());
-       allocp = --p;
-       ASSERT(testbusy(p->ptr));
-       p->ptr = clearbusy(p->ptr);
-       ASSERT(p->ptr > allocp && p->ptr <= alloct);
+       register union overhead *op;
+       register int rnu;       /* 2^rnu bytes will be requested */
+       register int nblks;     /* become nblks blocks of the desired size */
+       register int siz;
+
+       if (nextf[bucket])
+               return;
+       /*
+        * Insure memory is allocated
+        * on a page boundary.  Should
+        * make getpageize call?
+        */
+       op = (union overhead *)sbrk(0);
+       if ((int)op & 0x3ff)
+               sbrk(1024 - ((int)op & 0x3ff));
+       /* take 2k unless the block is bigger than that */
+       rnu = (bucket <= 8) ? 11 : bucket + 3;
+       nblks = 1 << (rnu - (bucket + 3));  /* how many blocks to get */
+       if (rnu < bucket)
+               rnu = bucket;
+       op = (union overhead *)sbrk(1 << rnu);
+       /* no more room! */
+       if ((int)op == -1)
+               return;
+       /*
+        * Round up to minimum allocation size boundary
+        * and deduct from block count to reflect.
+        */
+       if ((int)op & 7) {
+               op = (union overhead *)(((int)op + 8) &~ 7);
+               nblks--;
+       }
+       /*
+        * Add new memory allocated to that on
+        * free list for this hash bucket.
+        */
+       nextf[bucket] = op;
+       siz = 1 << (bucket + 3);
+       while (--nblks > 0) {
+               op->ov_next = (union overhead *)((caddr_t)op + siz);
+               op = (union overhead *)((caddr_t)op + siz);
+       }
+}
+
+free(cp)
+       char *cp;
+{   
+       register int size;
+       register union overhead *op;
+
+       if (cp == NULL)
+               return;
+       op = (union overhead *)((caddr_t)cp - sizeof (union overhead));
+#ifdef debug
+       ASSERT(op->ov_magic == MAGIC);          /* make sure it was in use */
+#else
+       if (op->ov_magic != MAGIC)
+               return;                         /* sanity */
+#endif
+#ifdef RCHECK
+       ASSERT(op->ov_rmagic == RMAGIC);
+       if (op->ov_index <= 13)
+               ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC);
+#endif
+       ASSERT(op->ov_index < NBUCKETS);
+       size = op->ov_index;
+       op->ov_next = nextf[size];
+       nextf[size] = op;
+#ifdef MSTATS
+       nmalloc[size]--;
+#endif

 }
 
 }
 

-/*     realloc(p, nbytes) reallocates a block obtained from malloc()
- *     and freed since last call of malloc()
- *     to have new size nbytes, and old content
- *     returns new location, or 0 on failure
-*/
+/*
+ * When a program attempts "storage compaction" as mentioned in the
+ * old malloc man page, it realloc's an already freed block.  Usually
+ * this is the last block it freed; occasionally it might be farther
+ * back.  We have to search all the free lists for the block in order
+ * to determine its bucket: 1st we make one pass thru the lists
+ * checking only the first block in each; if that fails we search
+ * ``realloc_srchlen'' blocks in each list for a match (the variable
+ * is extern so the caller can modify it).  If that fails we just copy
+ * however many bytes was given to realloc() and hope it's not huge.
+ */
+int realloc_srchlen = 4;       /* 4 should be plenty, -1 =>'s whole list */

 
 char *
 
 char *

-realloc(p, nbytes)
-register union store *p;
-unsigned nbytes;
-{
-       register union store *q;
-       union store *s, *t;
-       register unsigned nw;
-       unsigned onw;
-
-       if(testbusy(p[-1].ptr))
-               free((char *)p);
-       onw = p[-1].ptr - p;
-       q = (union store *)malloc(nbytes);
-       if(q==NULL || q==p)
-               return((char *)q);
-       s = p;
-       t = q;
-       nw = (nbytes+WORD-1)/WORD;
-       if(nw<onw)
-               onw = nw;
-       while(onw--!=0)
-               *t++ = *s++;
-       if(q<p && q+nw>=p)
-               (q+(q+nw-p))->ptr = allocx;
-       return((char *)q);
+realloc(cp, nbytes)
+       char *cp; 
+       unsigned nbytes;
+{   
+       register u_int onb;
+       union overhead *op;
+       char *res;
+       register int i;
+       int was_alloced = 0;
+
+       if (cp == NULL)
+               return (malloc(nbytes));
+       op = (union overhead *)((caddr_t)cp - sizeof (union overhead));
+       if (op->ov_magic == MAGIC) {
+               was_alloced++;
+               i = op->ov_index;
+       } else {
+               /*
+                * Already free, doing "compaction".
+                *
+                * Search for the old block of memory on the
+                * free list.  First, check the most common
+                * case (last element free'd), then (this failing)
+                * the last ``realloc_srchlen'' items free'd.
+                * If all lookups fail, then assume the size of
+                * the memory block being realloc'd is the
+                * smallest possible.
+                */
+               if ((i = findbucket(op, 1)) < 0 &&
+                   (i = findbucket(op, realloc_srchlen)) < 0)
+                       i = 0;
+       }
+       onb = (1 << (i + 3)) - sizeof (*op) - RSLOP;
+       /* avoid the copy if same size block */
+       if (was_alloced &&
+           nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP)
+               return(cp);
+       if ((res = malloc(nbytes)) == NULL)
+               return (NULL);
+       if (cp != res)                  /* common optimization */
+               bcopy(cp, res, (nbytes < onb) ? nbytes : onb);
+       if (was_alloced)
+               free(cp);
+       return (res);

 }
 
 }
 

-#ifdef debug
-allock()
+/*
+ * Search ``srchlen'' elements of each free list for a block whose
+ * header starts at ``freep''.  If srchlen is -1 search the whole list.
+ * Return bucket number, or -1 if not found.
+ */
+static
+findbucket(freep, srchlen)
+       union overhead *freep;
+       int srchlen;

 {
 {

-#ifdef longdebug
-       register union store *p;
-       int x;
-       x = 0;
-       for(p= &allocs[0]; clearbusy(p->ptr) > p; p=clearbusy(p->ptr)) {
-               if(p==allocp)
-                       x++;
+       register union overhead *p;
+       register int i, j;
+
+       for (i = 0; i < NBUCKETS; i++) {
+               j = 0;
+               for (p = nextf[i]; p && j != srchlen; p = p->ov_next) {
+                       if (p == freep)
+                               return (i);
+                       j++;
+               }

        }
        }

-       ASSERT(p==alloct);
-       return(x==1|p==allocp);
-#else
-       return(1);
-#endif
+       return (-1);
+}
+
+#ifdef MSTATS
+/*
+ * mstats - print out statistics about malloc
+ * 
+ * Prints two lines of numbers, one showing the length of the free list
+ * for each size category, the second showing the number of mallocs -
+ * frees for each size category.
+ */
+mstats(s)
+       char *s;
+{
+       register int i, j;
+       register union overhead *p;
+       int totfree = 0,
+       totused = 0;
+
+       fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s);
+       for (i = 0; i < NBUCKETS; i++) {
+               for (j = 0, p = nextf[i]; p; p = p->ov_next, j++)
+                       ;
+               fprintf(stderr, " %d", j);
+               totfree += j * (1 << (i + 3));
+       }
+       fprintf(stderr, "\nused:\t");
+       for (i = 0; i < NBUCKETS; i++) {
+               fprintf(stderr, " %d", nmalloc[i]);
+               totused += nmalloc[i] * (1 << (i + 3));
+       }
+       fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n",
+           totused, totfree);

 }
 #endif
 }
 #endif