mmap

not know Scala has no such concept), its type is not modifiable, if you want to define a modifiable type needs to be shown, as shown in Figure 2. Figure 2 The difference between mutable and immutable can be preliminarily understood by naming, the former can modify the content, and the latter cannot be modified after initialization. As shown in Figure 3, adding elements to the map and mmap in Figure 2, the map failed while trying the + = operation, a

Function: Mmap ()Function: Creates a memory map area, maps the file data on disk to memory, and the user can modify the disk file through memory.Advantages: High EfficiencyCons: Do not block, trouble (for efficiency is not very high demand advice with piping)Function Prototypes:#include void *mmap (voidint int int FD, off_t offset); int munmap (void *addr, size_t length);

", getpagesize ());} 　 Malloc (configure memory space) Related functions Calloc, free, realloc, BRK Header file # Include Define functions Void * malloc (size_t size ); Function Description Malloc () is used to configure the memory space, which is determined by the specified size. Return Value If the configuration is successful, a pointer is returned. If the configuration fails, null is returned. Example

Inter-process communication in Linux (5): Shared Memory (2) The system calls MMAP () to map a common file to implement shared memory. System V maps files in the SHM of a special file system to implement shared memory communication between processes. That is to say, each shared memory area corresponds to a file in the shm of the special File System (this is linked through the shmid_kernel structure), and will be elaborated later. 1. Principle of System

", getpagesize ());} Malloc (configure memory space) Related functions Calloc, free, realloc, BRK Header file # Include Define functions Void * malloc (size_t size ); Function Description Malloc () is used to configure the memory space, which is determined by the specified size. Return Value If the configuration is successful, a pointer is returned. If the configuration fails, null is returned. Example V

/Dev/MEM: full image of physical memory. It can be used to access the physical memory. /Dev/kmem: The full image of the virtual memory seen by the kernel. Can be used to access the contents of the kernel. /Dev/MEM is used to access physical Io devices, for example, X is used to access the physical memory of the graphics card or access gpio in embedded systems. Use The method is generally open and then MMAP can use the address after map to access the p

The/dev/MEM driver provided in the Linux Kernel provides a channel for us to read and write the physical address of the memory. The following describes two methods to read and write physical addresses Using Mem Device Files: one is a device driver and the other is a system call. First, let's take a look at the mem device file./dev/MEM is a character device in Linux. The source file is ~ /Drivers/Char/MEM. C. This device file is used to read and write physical addresses. The content is the addres

Reprinted from http://www.ibm.com/developerworks/cn/linux/l-ipc/part5/index2.html The system calls MMAP () to map a common file to implement shared memory. System V maps files in the SHM of a special file system to implement shared memory communication between processes. That is to say, each shared memory area corresponds to a file in the shm of the special File System (this is linked through the shmid_kernel structure), and will be elaborated later.

Directory 1. Write in front 2.devmem use 3. Application Layer 4. Kernel Layer 1. Write in frontRecently, when debugging, you need to access physical memory at the user level, and the application layer can use the devmem tool to access the physical address. View the source code, is actually the /dev/mem operation, through the mmap can map the physical address to the virtual address of the user space, completes the reading and

automatic function to prevent the second process from reading the shared memory before the write operation of the first process ends. The programmer is responsible for the synchronization of shared memory access. Optional Synchronization Methods include mutex lock, condition variable, read/write lock, record lock, and traffic signal. Related functions 1 MMAP () function 2 Function: maps a file or POSIX shared memory area object to the addres

support a display device in an embedded system. The frame buffer device is a standard character device. The primary device number is 29, and the secondary device number ranges from 0 to 31. Corresponding to/dev/fb0-/dev/fb31 respectively. Through/dev/FB, application operations mainly include: 1. read/write/dev/FB: equivalent to the read/write screen buffer. For example, you can use the CP/dev/fb0 TMP command to copy the content of the current screen to a file, the command cp tmp>/dev/fb0 direct

This is a creation in Article, where the information may have evolved or changed. Plug-in storage engine API MONGODB3.0 introduced the plug-in storage Engine API, which makes it easy for third-party storage engine vendors to join MongoDB, a change that undoubtedly references MySQL's design philosophy. At present, in addition to the early Mmap storage engine, Wiredtiger and ROCKSDB have completed the support for MongoDB, the former is the acquisition o

an issue caused by a process memory layout exceptionThe previous period of time the business reflects a certain type of server update bash, SSH connected to the occasional login failed, the client spit error message as follows:Figure-0This version of Bash is customized for the Department, but the implementation has not changed the original logic, but added some monitoring functions, then where do these errors come from?Is it bash's pot?From the above error message can be guessed that the excepti

in-page address two parts, is implemented by the machine hardware. The length of the segment is not fixed and is determined by the user to write the program, usually by the compilation system when the source program compiled according to the nature of the information to be divided. The page system address space is one-dimensional, that is, a single linear address space, where programmers can represent an address simply by using an identifier. The job address space of the segment is two-dime

) {size_t pagesize = Glro (dl_pagesize); Char *p1, *P2; unsigned long ul; Heap_info *h; if (size + Top_pad First, adjust the size of the memory that needs to be allocated. Aligned_heap_area represents the end address of the last mmap allocation and, if present, attempts to allocate the size of heap_max_size memory from that address first. Mmap the last is the system call, the correspondin

design philosophy. At present, in addition to the early Mmap storage engine, Wiredtiger and ROCKSDB have completed the support for MongoDB, the former is the acquisition of MongoDB company is directly introduced into the MONGODB 3.0 version. The introduction of the plug-in storage engine API has made it possible for MongoDB to enrich its arsenal to handle more different types of business, with memory storage engines, transactional storage engines, an

the memory hierarchy, the data on the disk (lower layer) is segmented into blocks that act as transmission units between the disk and main memory (higher). The VM system handles this problem by dividing the virtual memory into blocks of fixed size called virtual pages (vitual PAGE,VP). The size of each virtual page is P = 2 ^ n bytes. Similarly, physical memory is split into physical pages (physical page,pp), and the size is also p-bytes (physical pages are also called page frames).At any one t

valuable physical memory . The kernel frees the physical page by releasing the linear area, finding its corresponding physical page, and releasing it all out of the process .char *p=malloc(2048) //这里只是分配了虚拟内存2048，并不占用实际内存。strcpy(p,”123”) //分配了物理页面，虽然只是使用了3个字节，但内存还是为它分配了2048字节的物理内存。free(p) //通过虚拟地址，找到其所对应的物理页面，释放物理页面，释放线性区。We know that the user's process and kernel are running at different levels, and the communication between the process and the kernel is done through system calls. Processes in

segmented into blocks that act as transmission units between the disk and main memory (higher). The VM system handles this problem by dividing the virtual memory into blocks of fixed size called virtual pages (vitual PAGE,VP). The size of each virtual page is P = 2 ^ n bytes. Similarly, physical memory is split into physical pages (physical page,pp), and the size is also p-bytes (physical pages are also called page frames).At any one time, the collection of virtual pages is divided into three d

The Unified Call uses MMAP () to map a common file to implement shared memory. System V maps files in the SHM of a special file system to implement shared memory communication between processes. That is to say, each shared memory area corresponds to a file in the shm of the special File System (this is linked through the shmid_kernel structure), and will be elaborated later. 1. Principle of System V shared memory Data to be shared between processes is