内存管理内幕--动态分配的选择、折衷和实现（三）

        /* Structure Definitions*//* Base structure that holds a refcount */struct refcountedstruct{	int refcount;}/* All refcounted structures must mirror struct * refcountedstruct for their first variables *//* Refcount maintenance functions *//* Increase reference count */void REF(void *data){	struct refcountedstruct *rstruct;	rstruct = (struct refcountedstruct *) data;	rstruct->refcount++;}/* Decrease reference count */void UNREF(void *data){	struct refcountedstruct *rstruct;	rstruct = (struct refcountedstruct *) data;	rstruct->refcount--;	/* Free the structure if there are no more users */	if(rstruct->refcount == 0)	{		free(rstruct);	}}      

        /* EXAMPLES OF USAGE *//* Data type to be refcounted */struct mydata{	int refcount; /* same as refcountedstruct */	int datafield1; /* Fields specific to this struct */	int datafield2;	/* other declarations would go here as appropriate */};/* Use the functions in code */void dosomething(struct mydata *data){	REF(data);	/* Process data */	/* when we are through */	UNREF(data);}struct mydata *globalvar1;/* Note that in this one, we don't decrease the * refcount since we are maintaining the reference * past the end of the function call through the * global variable */void storesomething(struct mydata *data){	REF(data); /* passed as a parameter */	globalvar1 = data;	REF(data); /* ref because of Assignment */	UNREF(data); /* Function finished */}    

        #include <obstack.h>#include <stdlib.h>/* Example code listing for using obstacks *//* Used for obstack macros (xmalloc is   a malloc function that exits if memory   is exhausted */#define obstack_chunk_alloc xmalloc#define obstack_chunk_free free/* Pools *//* Only permanent allocations should go in this pool */struct obstack *global_pool;/* This pool is for per-connection data */struct obstack *connection_pool;/* This pool is for per-request data */struct obstack *request_pool;void allocation_failed(){	exit(1);}int main(){	/* Initialize Pools */	global_pool = (struct obstack *)		xmalloc (sizeof (struct obstack));	obstack_init(global_pool);	connection_pool = (struct obstack *)		xmalloc (sizeof (struct obstack));	obstack_init(connection_pool);	request_pool = (struct obstack *)		xmalloc (sizeof (struct obstack));	obstack_init(request_pool);	/* Set the error handling function */	obstack_alloc_failed_handler = &allocation_failed;	/* Server main loop */	while(1)	{		wait_for_connection();		/* We are in a connection */		while(more_requests_available())		{			/* Handle request */			handle_request();			/* Free all of the memory allocated			 * in the request pool			 */			obstack_free(request_pool, NULL);		}		/* We're finished with the connection, time		 * to free that pool		 */		obstack_free(connection_pool, NULL);	}}int handle_request(){	/* Be sure that all object allocations are allocated	 * from the request pool	 */	int bytes_i_need = 400;	void *data1 = obstack_alloc(request_pool, bytes_i_need);	/* Do stuff to process the request */	/* return */	return 0;}