UNIX 7th Ed. - /usr/src/libc/gen/malloc.c

   1: #ifdef debug
   2: #define ASSERT(p) if(!(p))botch("p");else
   3: botch(s)
   4: char *s;
   5: {
   6:     printf("assertion botched: %s\n",s);
   7:     abort();
   8: }
   9: #else
  10: #define ASSERT(p)
  11: #endif
  12: 
  13: /*	avoid break bug */
  14: #ifdef pdp11
  15: #define GRANULE 64
  16: #else
  17: #define GRANULE 0
  18: #endif
  19: /*	C storage allocator
  20:  *	circular first-fit strategy
  21:  *	works with noncontiguous, but monotonically linked, arena
  22:  *	each block is preceded by a ptr to the (pointer of)
  23:  *	the next following block
  24:  *	blocks are exact number of words long
  25:  *	aligned to the data type requirements of ALIGN
  26:  *	pointers to blocks must have BUSY bit 0
  27:  *	bit in ptr is 1 for busy, 0 for idle
  28:  *	gaps in arena are merely noted as busy blocks
  29:  *	last block of arena (pointed to by alloct) is empty and
  30:  *	has a pointer to first
  31:  *	idle blocks are coalesced during space search
  32:  *
  33:  *	a different implementation may need to redefine
  34:  *	ALIGN, NALIGN, BLOCK, BUSY, INT
  35:  *	where INT is integer type to which a pointer can be cast
  36: */
  37: #define INT int
  38: #define ALIGN int
  39: #define NALIGN 1
  40: #define WORD sizeof(union store)
  41: #define BLOCK 1024  /* a multiple of WORD*/
  42: #define BUSY 1
  43: #define NULL 0
  44: #define testbusy(p) ((INT)(p)&BUSY)
  45: #define setbusy(p) (union store *)((INT)(p)|BUSY)
  46: #define clearbusy(p) (union store *)((INT)(p)&~BUSY)
  47: 
  48: union store { union store *ptr;
  49:           ALIGN dummy[NALIGN];
  50:           int calloc;   /*calloc clears an array of integers*/
  51: };
  52: 
  53: static  union store allocs[2];  /*initial arena*/
  54: static  union store *allocp;    /*search ptr*/
  55: static  union store *alloct;    /*arena top*/
  56: static  union store *allocx;    /*for benefit of realloc*/
  57: char    *sbrk();
  58: 
  59: char *
  60: malloc(nbytes)
  61: unsigned nbytes;
  62: {
  63:     register union store *p, *q;
  64:     register nw;
  65:     static temp;    /*coroutines assume no auto*/
  66: 
  67:     if(allocs[0].ptr==0) {  /*first time*/
  68:         allocs[0].ptr = setbusy(&allocs[1]);
  69:         allocs[1].ptr = setbusy(&allocs[0]);
  70:         alloct = &allocs[1];
  71:         allocp = &allocs[0];
  72:     }
  73:     nw = (nbytes+WORD+WORD-1)/WORD;
  74:     ASSERT(allocp>=allocs && allocp<=alloct);
  75:     ASSERT(allock());
  76:     for(p=allocp; ; ) {
  77:         for(temp=0; ; ) {
  78:             if(!testbusy(p->ptr)) {
  79:                 while(!testbusy((q=p->ptr)->ptr)) {
  80:                     ASSERT(q>p&&q<alloct);
  81:                     p->ptr = q->ptr;
  82:                 }
  83:                 if(q>=p+nw && p+nw>=p)
  84:                     goto found;
  85:             }
  86:             q = p;
  87:             p = clearbusy(p->ptr);
  88:             if(p>q)
  89:                 ASSERT(p<=alloct);
  90:             else if(q!=alloct || p!=allocs) {
  91:                 ASSERT(q==alloct&&p==allocs);
  92:                 return(NULL);
  93:             } else if(++temp>1)
  94:                 break;
  95:         }
  96:         temp = ((nw+BLOCK/WORD)/(BLOCK/WORD))*(BLOCK/WORD);
  97:         q = (union store *)sbrk(0);
  98:         if(q+temp+GRANULE < q) {
  99:             return(NULL);
 100:         }
 101:         q = (union store *)sbrk(temp*WORD);
 102:         if((INT)q == -1) {
 103:             return(NULL);
 104:         }
 105:         ASSERT(q>alloct);
 106:         alloct->ptr = q;
 107:         if(q!=alloct+1)
 108:             alloct->ptr = setbusy(alloct->ptr);
 109:         alloct = q->ptr = q+temp-1;
 110:         alloct->ptr = setbusy(allocs);
 111:     }
 112: found:
 113:     allocp = p + nw;
 114:     ASSERT(allocp<=alloct);
 115:     if(q>allocp) {
 116:         allocx = allocp->ptr;
 117:         allocp->ptr = p->ptr;
 118:     }
 119:     p->ptr = setbusy(allocp);
 120:     return((char *)(p+1));
 121: }
 122: 
 123: /*	freeing strategy tuned for LIFO allocation
 124: */
 125: free(ap)
 126: register char *ap;
 127: {
 128:     register union store *p = (union store *)ap;
 129: 
 130:     ASSERT(p>clearbusy(allocs[1].ptr)&&p<=alloct);
 131:     ASSERT(allock());
 132:     allocp = --p;
 133:     ASSERT(testbusy(p->ptr));
 134:     p->ptr = clearbusy(p->ptr);
 135:     ASSERT(p->ptr > allocp && p->ptr <= alloct);
 136: }
 137: 
 138: /*	realloc(p, nbytes) reallocates a block obtained from malloc()
 139:  *	and freed since last call of malloc()
 140:  *	to have new size nbytes, and old content
 141:  *	returns new location, or 0 on failure
 142: */
 143: 
 144: char *
 145: realloc(p, nbytes)
 146: register union store *p;
 147: unsigned nbytes;
 148: {
 149:     register union store *q;
 150:     union store *s, *t;
 151:     register unsigned nw;
 152:     unsigned onw;
 153: 
 154:     if(testbusy(p[-1].ptr))
 155:         free((char *)p);
 156:     onw = p[-1].ptr - p;
 157:     q = (union store *)malloc(nbytes);
 158:     if(q==NULL || q==p)
 159:         return((char *)q);
 160:     s = p;
 161:     t = q;
 162:     nw = (nbytes+WORD-1)/WORD;
 163:     if(nw<onw)
 164:         onw = nw;
 165:     while(onw--!=0)
 166:         *t++ = *s++;
 167:     if(q<p && q+nw>=p)
 168:         (q+(q+nw-p))->ptr = allocx;
 169:     return((char *)q);
 170: }
 171: 
 172: #ifdef debug
 173: allock()
 174: {
 175: #ifdef longdebug
 176:     register union store *p;
 177:     int x;
 178:     x = 0;
 179:     for(p= &allocs[0]; clearbusy(p->ptr) > p; p=clearbusy(p->ptr)) {
 180:         if(p==allocp)
 181:             x++;
 182:     }
 183:     ASSERT(p==alloct);
 184:     return(x==1|p==allocp);
 185: #else
 186:     return(1);
 187: #endif
 188: }
 189: #endif

Defined functions

Defined variables

Defined union's

Defined macros