openfam::fam::fam_subtract

Atomically subtract a value from some data item in FAM.

Synopsis

void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset, int32_t value);

void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset, int64_t value);

void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset, uint32_t value);

void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset, uint64_t value);

void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset, float value);

void fam_subtract(Fam_Descriptor *descriptor, uint64_t offset, double value);

Description

These methods atomically subtract a value from an existing value in FAM.

Input Arguments

Name	Description
descriptor	Descriptor associated with the data item.
offset	Offset within the data item in FAM where value is located.
value	Value to be subtracted from the existing value at the given location.

Return Values

None. Throws Fam_Exception on error.

Fam Error Numbers

Error	Description
FAM_ERR_INVALID	API called with incorrect parameters.
FAM_ERR_NOPERM	Caller does not have access rights.
FAM_ERR_LIBFABRIC	Libfabric error occurred.
FAM_ERR_NOTFOUND	Item not found in the region.
FAM_ERR_RPC	Communication error from grpc layer.
FAM_ERR_RPC_CLIENT_NOTFOUND	RPC service not available.
FAM_ERR_METADATA	Metadata service error.
FAM_ERR_MEMORY	Memory service error.
FAM_ERR_RESOURCE	Resource not available.

Notes

These methods atomically subtract a value to an existing value in FAM, and return before the operation is complete. Note that the offset argument must point to the correct value for the data type. Availability of these methods is dependent on hardware support for the operations.

Successful completion of a subsequent fam_quiet() call ensures the completion of this atomic operation.

Example

#include <string.h>
#include <fam/fam.h>
#include <fam/fam_exception.h>
using namespace std;
using namespace openfam;
	
int main(void) {
	fam *myFam = new fam();
	// ... Initialization code here
	try {
		// look up the descriptor to a previously allocated data item
		// (an integer array with at least 10 elements)
		Fam_Descriptor *descriptor = myFam->fam_lookup("myItem", "myRegion");
	
		//Atomically subtract a value of 50 from the first integer element in the array
		myFam->fam_subtract(descriptor, 0, 50);
	
		// ensure that the subtract operation is complete
		myFam->fam_quiet();
	
		// The first integer in FAM is now subtracted with a value of 50
	 } catch (Fam_Exception &e) {
		printf("fam API failed: %d: %s\n", e.fam_error(), e.fam_error_msg());
	 }
	 // ... Finalization code follows
}