rds_malloc

NAME

rds_malloc - allocate recoverable heap storage

SYNOPSIS

#include "rds.h"

int rds_malloc (size, tid, err);
unsigned long size;  /* length of allocation request */
rvm_tid_t     *tid;  /* optional pointer to transaction identifier */
int           *err;  /* pointer to error return location */

DESCRIPTION

rds_malloc allocates from the recoverable heap a block large enough to hold the request, specified in bytes by the size parameter. The address of the allocated block is returned as type int and must be cast to the desired type. If the request cannot be satisfied, zero is returned, and the err parameter is set to the appropriate error code.

Because allocation actions in the recoverable heap must be done via transactions, rds_malloc offers two choices for the transaction. In the first case, rds_malloc 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 modified, but uncommitted, free lists are visible to other RDS actions.

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_malloc 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, an explicit rds_free must be done if the allocating transaction later aborts.

DIAGNOSTICS

SUCCESS: success (error will be 0)
ENO_ROOM: RDS heap exhausted
ECORRUPT: heap corruption detected
EHEAP_INIT: RDS not initialized
RVM error codes: various errors from RVM subsystem

AUTHOR

David C. Steere

BUGS

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