有关IOS内存读写冲突
在写内存相关代码时,获取已使用内存代码中报错
let hostPort: mach_port_t = mach_host_self()
var host_size = mach_msg_type_number_t(MemoryLayout<vm_statistics_data_t>.stride / MemoryLayout<integer_t>.stride)
var pagesize: vm_size_t = 0
host_page_size(hostPort, &pagesize)
var vmStat1: vm_statistics = vm_statistics_data_t()
let status: kern_return_t = withUnsafeMutableBytes(of: &vmStat1) {
let boundPtr = $0.baseAddress?.bindMemory(to: Int32.self, capacity: MemoryLayout.size(ofValue: vmStat1) / MemoryLayout<Int32>.stride)
return host_statistics(hostPort, HOST_VM_INFO, boundPtr, &host_size)
}
if status == KERN_SUCCESS {
let usedMemory = Int64(vm_size_t(vmStat1.active_count + vmStat1.inactive_count + vmStat1.wire_count) * pagesize)
return usedMemory
} else {
print("Failed to get Virtual memory inforor")
return 0
}
这一段代码报错
let status: kern_return_t = withUnsafeMutableBytes(of: &vmStat1) {
let boundPtr = $0.baseAddress?.bindMemory(to: Int32.self, capacity: MemoryLayout.size(ofValue: vmStat1) / MemoryLayout<Int32>.stride)
return host_statistics(hostPort, HOST_VM_INFO, boundPtr, &host_size)
}
Overlapping accesses to 'vmStat1', but modification requires exclusive access; consider copying to a local variable
对“vmStat1”的重叠访问,但修改需要独占访问权限;考虑复制到局部变量
看了一下
在withUnsafeMutableBytes(of: &vmStat1)
这里是用了inout关键字
@inlinable public func withUnsafeMutableBytes<T, Result>(of value: inout T, _ body: (UnsafeMutableRawBufferPointer) throws -> Result) rethrows -> Result
相当于将vmStat1的指针传了进去,拿到了vmStat1的写权限
而下一段代码
let boundPtr = $0.baseAddress?.bindMemory(to: Int32.self, capacity: MemoryLayout.size(ofValue: vmStat1) / MemoryLayout<Int32>.stride)
又拿到了vmStat1的读权限
而内存访问冲突:对同一块内存,同时进行读写操作,或者同时进行多个写入操作时,就会造成内存访问冲突。
根据编译器建议,可以拷贝给一个局部变量vmStat
也就是
var vmStat = vmStat1
let status: kern_return_t = withUnsafeMutableBytes(of: &vmStat) {
let boundPtr = $0.baseAddress?.bindMemory(to: Int32.self, capacity: MemoryLayout.size(ofValue: vmStat1) / MemoryLayout<Int32>.stride)
return host_statistics(hostPort, HOST_VM_INFO, boundPtr, &host_size)
}
vmStat1 = vmStat
将这个局部变量的指针传进去做修改,修改完之后在将其值赋回给vmStat1
这样就不会同时对vmStat1进行读写操作导致内存冲突
在withUnsafeMutableBytes这个方法中的注释中也有写到
在body这个闭包持续时间中,也就是
{
let boundPtr = $0.baseAddress?.bindMemory(to: Int32.self, capacity: MemoryLayout.size(ofValue: vmStat1) / MemoryLayout<Int32>.stride)
return host_statistics(hostPort, HOST_VM_INFO, boundPtr, &host_size)
}
这一段代码,是无法直接访问到value也就是上面的vmStat1变量的,只有在这个闭包return之后才能访问,所以将vmStat1拷贝到vmStat,value现在是vmStat,在闭包中访问vmStat1就不会有内存访问冲突
标签:return,vmStat1,读写,IOS,host,let,内存,size,MemoryLayout From: https://www.cnblogs.com/r1cardo/p/17289372.html