atomic_pointer.go

Documentation: runtime

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime
     6  
     7  import (
     8  	"runtime/internal/atomic"
     9  	"unsafe"
    10  )
    11  
    12  // These functions cannot have go:noescape annotations,
    13  // because while ptr does not escape, new does.
    14  // If new is marked as not escaping, the compiler will make incorrect
    15  // escape analysis decisions about the pointer value being stored.
    16  // Instead, these are wrappers around the actual atomics (casp1 and so on)
    17  // that use noescape to convey which arguments do not escape.
    18  
    19  // atomicstorep performs *ptr = new atomically and invokes a write barrier.
    20  //
    21  //go:nosplit
    22  func atomicstorep(ptr unsafe.Pointer, new unsafe.Pointer) {
    23  	writebarrierptr_prewrite((*uintptr)(ptr), uintptr(new))
    24  	atomic.StorepNoWB(noescape(ptr), new)
    25  }
    26  
    27  //go:nosplit
    28  func casp(ptr *unsafe.Pointer, old, new unsafe.Pointer) bool {
    29  	// The write barrier is only necessary if the CAS succeeds,
    30  	// but since it needs to happen before the write becomes
    31  	// public, we have to do it conservatively all the time.
    32  	writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
    33  	return atomic.Casp1((*unsafe.Pointer)(noescape(unsafe.Pointer(ptr))), noescape(old), new)
    34  }
    35  
    36  // Like above, but implement in terms of sync/atomic's uintptr operations.
    37  // We cannot just call the runtime routines, because the race detector expects
    38  // to be able to intercept the sync/atomic forms but not the runtime forms.
    39  
    40  //go:linkname sync_atomic_StoreUintptr sync/atomic.StoreUintptr
    41  func sync_atomic_StoreUintptr(ptr *uintptr, new uintptr)
    42  
    43  //go:linkname sync_atomic_StorePointer sync/atomic.StorePointer
    44  //go:nosplit
    45  func sync_atomic_StorePointer(ptr *unsafe.Pointer, new unsafe.Pointer) {
    46  	writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
    47  	sync_atomic_StoreUintptr((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
    48  }
    49  
    50  //go:linkname sync_atomic_SwapUintptr sync/atomic.SwapUintptr
    51  func sync_atomic_SwapUintptr(ptr *uintptr, new uintptr) uintptr
    52  
    53  //go:linkname sync_atomic_SwapPointer sync/atomic.SwapPointer
    54  //go:nosplit
    55  func sync_atomic_SwapPointer(ptr *unsafe.Pointer, new unsafe.Pointer) unsafe.Pointer {
    56  	writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
    57  	old := unsafe.Pointer(sync_atomic_SwapUintptr((*uintptr)(noescape(unsafe.Pointer(ptr))), uintptr(new)))
    58  	return old
    59  }
    60  
    61  //go:linkname sync_atomic_CompareAndSwapUintptr sync/atomic.CompareAndSwapUintptr
    62  func sync_atomic_CompareAndSwapUintptr(ptr *uintptr, old, new uintptr) bool
    63  
    64  //go:linkname sync_atomic_CompareAndSwapPointer sync/atomic.CompareAndSwapPointer
    65  //go:nosplit
    66  func sync_atomic_CompareAndSwapPointer(ptr *unsafe.Pointer, old, new unsafe.Pointer) bool {
    67  	writebarrierptr_prewrite((*uintptr)(unsafe.Pointer(ptr)), uintptr(new))
    68  	return sync_atomic_CompareAndSwapUintptr((*uintptr)(noescape(unsafe.Pointer(ptr))), uintptr(old), uintptr(new))
    69  }
    70
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