Question

我mmap()匿名VMA。 pthreads如何处理该VMA？我想要为每个线程复制带有内存的vma。为此目的我需要哪些旗帜？

Answer 1

我mmap（）是一个匿名的VMA。 pthreads如何处理该VMA？

“pthreads”（Linux中线程的用户空间库）没有特别处理来自mmap的新VMA。

我希望为每个线程复制带有内存的vma。

你不能，因为单个进程的每个线程都有相同的VMA。

glibc中的默认pthread实现 - NPTL，使用带有clone标志的CLONE_VM系统调用： http://code.metager.de/source/xref/gnu/glibc/sysdeps/unix/sysv/linux/createthread.c

47 static int
48 create_thread (struct pthread *pd, const struct pthread_attr *attr,
49         bool stopped_start, STACK_VARIABLES_PARMS, bool *thread_ran)
50 {
66  /* We rely heavily on various flags the CLONE function understands:
67
68     CLONE_VM, CLONE_FS, CLONE_FILES
69  These flags select semantics with shared address space and
70  file descriptors according to what POSIX requires.

94  const int clone_flags = (CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SYSVSEM
95             | CLONE_SIGHAND | CLONE_THREAD
96             | CLONE_SETTLS | CLONE_PARENT_SETTID
97             | CLONE_CHILD_CLEARTID
98             | 0);
99

102  if (__glibc_unlikely (ARCH_CLONE (&start_thread, STACK_VARIABLES_ARGS,
103                 clone_flags, pd, &pd->tid, tp, &pd->tid)

man page of clone说：

   CLONE_VM (since Linux 2.0)
          If CLONE_VM is set, the calling process and the child process
          run in the same memory space.  In particular, memory writes
          performed by the calling process or by the child process are
          also visible in the other process.  Moreover, any memory
          mapping or unmapping performed with mmap(2) or munmap(2) by
          the child or calling process also affects the other process.

因此，使用mmap（2）执行的任何内存映射或取消映射或通过一个线程执行的munmap（2）都可以被linux glibc pthreads中的所有进程线程看到。 mmap不需要额外的标志; CLONE_VM标志已经给予克隆。

mmap（）和pthreads - 复制VMA

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