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40 lines
1.0 KiB
Markdown
40 lines
1.0 KiB
Markdown
---
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title: "18-processes-sharing-and-threads"
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aliases:
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tags:
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- cosc204
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- lecture
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---
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# Shared memory for processes
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Can't assume all variables are initally zero.
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OS decide which process maps who which physical address
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memory mapping `mmap` is a family of system calls:
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- allow two processes to share some region of their memory space.
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- achieved by creating a memory region that can be shared by other processes
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shared memory by two processes mapping to the same file or using fork() after mmap()
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``` c
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random_fd = open("/home/hzy/test/zero", O_RDWR);
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ptr = mmap(NULL, 10240, PROT_READ|PROT_WRITE,
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MAP_SHARED | MAP_FILE, random_fd, 0);
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```
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private mapping is often ysed to set up new memory sections.
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``` c
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fd = open("mmap_test_file", O_RDWR); p
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tr = mmap(NULL, 10240, PROT_READ|PROT_WRITE,
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MAP_PRIVATE|MAP_FILE, fd, 0);
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```
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# Threads
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Lightweight process - shares everything except the stack
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