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Text File | 1998-04-08 | 6.3 KB | 158 lines

! -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*- ! ! The contents of this file are subject to the Netscape Public License ! Version 1.0 (the "NPL"); you may not use this file except in ! compliance with the NPL. You may obtain a copy of the NPL at ! http://www.mozilla.org/NPL/ ! ! Software distributed under the NPL is distributed on an "AS IS" basis, ! WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL ! for the specific language governing rights and limitations under the ! NPL. ! ! The Initial Developer of this code under the NPL is Netscape ! Communications Corporation. Portions created by Netscape are ! Copyright (C) 1998 Netscape Communications Corporation. All Rights ! Reserved. ! ! ! atomic increment, decrement and swap routines for V8+ sparc (ultrasparc) ! using CAS (compare-and-swap) atomic instructions ! ! this MUST be compiled with an ultrasparc-aware assembler ! ! standard asm linkage macros; this module must be compiled ! with the -P option (use C preprocessor) #include <sys/asm_linkage.h> ! ====================================================================== ! ! Perform the sequence a = a + 1 atomically with respect to other ! fetch-and-adds to location a in a wait-free fashion. ! ! usage : val = PR_AtomicIncrement(address) ! return: current value (you'd think this would be old val) ! ! ----------------------- ! Note on REGISTER USAGE: ! as this is a LEAF procedure, a new stack frame is not created; ! we use the caller's stack frame so what would normally be %i (input) ! registers are actually %o (output registers). Also, we must not ! overwrite the contents of %l (local) registers as they are not ! assumed to be volatile during calls. ! ! So, the registers used are: ! %o0 [input] - the address of the value to increment ! %o1 [local] - work register ! %o2 [local] - work register ! %o3 [local] - work register ! ----------------------- ENTRY(PR_AtomicIncrement) ! standard assembler/ELF prologue retryAI: ld [%o0], %o2 ! set o2 to the current value add %o2, 0x1, %o3 ! calc the new value mov %o3, %o1 ! save the return value cas [%o0], %o2, %o3 ! atomically set if o0 hasn't changed cmp %o2, %o3 ! see if we set the value bne retryAI ! if not, try again nop ! empty out the branch pipeline retl ! return back to the caller mov %o1, %o0 ! set the return code to the new value SET_SIZE(PR_AtomicIncrement) ! standard assembler/ELF epilogue ! ! end ! ! ====================================================================== ! ! ====================================================================== ! ! Perform the sequence a = a - 1 atomically with respect to other ! fetch-and-decs to location a in a wait-free fashion. ! ! usage : val = PR_AtomicDecrement(address) ! return: current value (you'd think this would be old val) ! ! ----------------------- ! Note on REGISTER USAGE: ! as this is a LEAF procedure, a new stack frame is not created; ! we use the caller's stack frame so what would normally be %i (input) ! registers are actually %o (output registers). Also, we must not ! overwrite the contents of %l (local) registers as they are not ! assumed to be volatile during calls. ! ! So, the registers used are: ! %o0 [input] - the address of the value to increment ! %o1 [local] - work register ! %o2 [local] - work register ! %o3 [local] - work register ! ----------------------- ENTRY(PR_AtomicDecrement) ! standard assembler/ELF prologue retryAD: ld [%o0], %o2 ! set o2 to the current value sub %o2, 0x1, %o3 ! calc the new value mov %o3, %o1 ! save the return value cas [%o0], %o2, %o3 ! atomically set if o0 hasn't changed cmp %o2, %o3 ! see if we set the value bne retryAD ! if not, try again nop ! empty out the branch pipeline retl ! return back to the caller mov %o1, %o0 ! set the return code to the new value SET_SIZE(PR_AtomicDecrement) ! standard assembler/ELF epilogue ! ! end ! ! ====================================================================== ! ! ====================================================================== ! ! Perform the sequence a = b atomically with respect to other ! fetch-and-stores to location a in a wait-free fashion. ! ! usage : old_val = PR_AtomicSet(address, newval) ! ! ----------------------- ! Note on REGISTER USAGE: ! as this is a LEAF procedure, a new stack frame is not created; ! we use the caller's stack frame so what would normally be %i (input) ! registers are actually %o (output registers). Also, we must not ! overwrite the contents of %l (local) registers as they are not ! assumed to be volatile during calls. ! ! So, the registers used are: ! %o0 [input] - the address of the value to increment ! %o1 [input] - the new value to set for [%o0] ! %o2 [local] - work register ! %o3 [local] - work register ! ----------------------- ENTRY(PR_AtomicSet) ! standard assembler/ELF prologue retryAS: ld [%o0], %o2 ! set o2 to the current value mov %o1, %o3 ! set up the new value cas [%o0], %o2, %o3 ! atomically set if o0 hasn't changed cmp %o2, %o3 ! see if we set the value bne retryAS ! if not, try again nop ! empty out the branch pipeline retl ! return back to the caller mov %o3, %o0 ! set the return code to the prev value SET_SIZE(PR_AtomicSet) ! standard assembler/ELF epilogue ! ! end ! ! ====================================================================== !