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atomic(D3oddi)

atomic -- quick atomic locks

Synopsis

#include <??>

void qadd<size> (void , int;
void qsub<size> (void , int;
void qand<size> (void , int;
void qxchg<size> (void , int;
void qor<size> (void , int;
void qbts<size> (void , int;
void qinc<size>(void );
void qdec<size>(void );
void qzero<size>(void );

Description

Arguments

Quick locks provide atomic arithmetic and bit operations for variables on multiprocessor systems. The name of each routine indicates the operation and size of its arguments. The last character(s) represents the argument type as follows:

l long ul unsigned long

i int ui unsigned int

w word (short) uw unsigned word (unsigned short)

b byte (char) ub unsigned byte (unsigned char)

Return values

None for addition, subtraction, and, exchange, or, increment, and zero.

Bit test/set functions return the result of the test.

Usage

The following tables show the full set of quick lock functions:

Quick locks with two parameters -- qaddl(void,long)

Operation long ulong int uint short ushort char uchar

addition qaddl qaddul qaddi qaddui qaddw qadduw qaddb qaddub

subtraction qsubl qsubul qsubi qsubui qsubw qsubuw qsubb qsubub

and qandl qandul qandi qandui qandw qanduw qandb qandub

exchange qxchgl qxchgul qxchgi qxchgui qxchgw qxchguw qxchgb qxchgub

or qorl qorul qori qorui qorw qoruw qorb qorub

Quick locks with one parameter --qincl(void)

Operation long ulong int uint short ushort char uchar

increment qincl qincul qinci qincui qincw qincuw qincb qincub

decrement qdecl qdecul qdeci qdecui qdecw qdecuw qdecb qdecub

zero qzerol qzeroul qzeroi qzeroui qzerow qzerouw qzerob qzeroub

Bit test/set locks

Operation long ulong int uint short ushort char uchar

bit test/set qbtsl qbtsul qbtsi qbtsui -- -- -- --

These routines use the 80*86 lock prefix instruction to lock the bus during the execution of the instruction. They should be used whenever a simple atomic action is all that is required such as incrementing a counter. They have less impact on performance than other locks.

The qbts family of functions do an atomic test and set of a bit in a field of bits. This is useful for semaphores and similar operations. If more than one bit is specified in the second parameter, the qbts function will test and set the least bit requested and silently ignore any others. Use the qorl family if multiple bits need to be set.

These operations cannot be split by an interrupt because they are executed as a single assembler instruction.

Context and synchronization

All contexts.

Hardware applicability

All

Version applicability

oddi: 3, 3mp, 4, 4mp, 5, 5mp, 6, 6mp

SVR5 DDI compatibility

These functions are not supported for DDI drivers. DDI drivers support atomic locks with a different set of functions. See ``Atomic locks'' in HDK Technical Reference.

References

clockb(D3oddi), lockb(D3oddi), ilockb(D3oddi)

``Atomic locks'' in HDK Technical Reference

Examples

The following calls illustrate the use of the qinc, qdec, qadd and qand functions:

   qincl(&my_arg);
   qdecb(&my_arg2);
   
   qaddl(&my_arg, 3);
   qandb(&my_arg2, 0x40);

Because a quick lock cannot be split up by an interrupt, the following two code fragments provide equivalent functionality, although the fragment on the right that uses qinc is more efficient:

   s=spl7();				qincl(&i);
   	i++;
   splx(s);

The following example illustrates the use of the qbts functions. This code references a buffer whose header has a bit that indicates whether the buffer is in use. The qbtsl function tests the bit, unconditionally sets it to mark that the buffer is busy, and returns the result of the test. On return, the bit is definitely set; the return value indicates whether this process "owns" the buffer or if someone else had it first.

   #define IN_USE 1
   
   int control_word;
   if (qbtsl(&control_word, IN_USE) ) {
   	/* buffer was in_use, we cannot use it */
   }
   else {
   	/* buffer was free, now marked busy, we can use it */
   }

l	long	ul	unsigned long
i	int	ui	unsigned int
w	word (short)	uw	unsigned word (unsigned short)
b	byte (char)	ub	unsigned byte (unsigned char)

Operation	long	ulong	int	uint	short	ushort	char	uchar
addition	qaddl	qaddul	qaddi	qaddui	qaddw	qadduw	qaddb	qaddub
subtraction	qsubl	qsubul	qsubi	qsubui	qsubw	qsubuw	qsubb	qsubub
and	qandl	qandul	qandi	qandui	qandw	qanduw	qandb	qandub
exchange	qxchgl	qxchgul	qxchgi	qxchgui	qxchgw	qxchguw	qxchgb	qxchgub
or	qorl	qorul	qori	qorui	qorw	qoruw	qorb	qorub