rds_prealloc(3)

NAME
rds_prealloc - initialize allocation pools

SYNOPSIS

#include "rds.h"
int rds_prealloc (size, nblocks, tid, err)
unsigned long size;    /* size of allocation request */
unsigned long nblocks; /* length of allocation request */
rvm_tid_t     *tid;    /* pointer to transaction identifer */
int           *err;    /* pointer to error return location */

DESCRIPTION
rds_prealloc assists applications in minimizing heap fragmentation by pre-allocating pools of blocks in sizes that the application is known to use in relatively large numbers. rds_prealloc is best called immediately after the heap is initialized, although it can be called anytime. When pools of several block sizes are pre-allocated, they should be allocated in increasing block size order so that the larger blocks are not split to make the smaller. The size parameter specifies the size, in bytes, of the blocks to be pre-allocated, and nblocks controls the number of blocks pre-allocated. Because allocation actions in the recoverable heap must be done via transactions, rds_prealloc offers two choices for the transaction. In the first case, rds_prealloc can be instructed to use an existing transaction begun in restore mode, by passing the address of a valid rvm_tid_t record in the tid parameter. This avoids extra transaction start and commit overhead and provides automatic deallocation if the transaction must later abort. However, no context swap can be permitted between allocation and transaction commit or abort since the uncommitted state is visible to other allocations. If context swaps cannot be prohibited, or the available transaction was started in no_restore mode, the tid parameter should be set to null, instructing rds_prealloc to start an internal transaction. This transaction will be committed in no_flush mode if the allocation is made, and aborted otherwise. In this case, if the allocating transaction later aborts, the pre-allocated blocks remain allocated.

DIAGNOSTICS

SUCCESS
    success

ENO_ROOM
    RDS heap exhausted

ECORRUPT
    RDS heap damaged

EHEAP_INIT
    RDS not initialized

positive values
    RVM return codes

SEE ALSO
rds_malloc(3), rds_init_heap(3), rds_zap_heap(3)

AUTHOR
David C. Steere

BUGS
The internal synchronization is not valid with pre-emptive threads.