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Date: Mon, 17 Dec 2007 10:13:08 -0800
From: Wayne Christopher <wayne AT 4raccoons DOT com>
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To: cygwin AT cygwin DOT com
Subject: Re: mmap failing
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My test program is attached.  This example works but in my real program 
the same write+close+mmap sequence did not.

It appears that calling fsync before the close sometimes avoids the 
error but not always.

This is Cygwin 1.5.24(0.156/4/2).

Any thoughts?  Thanks,

    Wayne

Corinna Vinschen wrote:
> On Dec 14 13:59, Wayne Christopher wrote:
>   
>> I have a 268MB file open for writing.  I close it and then
>> immediately try to mmap() it, and a get ENOMEM.  However I do have the
>> VM space available and can malloc() the size of the file right after the 
>> failure.  Also, I have mmap()'ed other similar files in the same program 
>> before this, but these had not just been closed.
>>
>> My initial guess was that it was timing related, but if I wait for 5
>> seconds and try again I still get the failure.
>>
>> I wasn't able to duplicate it in a small example since my app has a bunch 
>> of threads and is doing other stuff at the same time.
>>
>> Any suggestions for solutions or workarounds?
>>     
>
> Not without testcase and version information.  Is that under 1.5.24-2
> or 1.5.25-x?  Could you test if the result differs between these two
> versions?  If so, how?
>
>
> Corinna
>
>   


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 name="mmcheck.c"
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 filename="mmcheck.c"

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <sys/unistd.h>

#define SIZE 268000000

main()
{
    char* fname = "test_file";
    char* data;
    int fd, i;
    struct stat sb;
    caddr_t base;
    
    data = malloc(SIZE);
    fd = open(fname, O_RDWR|O_CREAT, 0666);
    assert(fd >= 0);
    
    i = write(fd, data, SIZE);
    assert(i == SIZE);
    close(fd);

    i = stat(fname, &sb);
    assert(i >= 0);
    
    assert(SIZE == sb.st_size);
    
    fd = open(fname, O_RDONLY, 0);
    assert(fd >= 0);
    
    base = (caddr_t) mmap(NULL, SIZE, PROT_READ, MAP_SHARED, fd, 0);
    printf("base = %ld\n", (long) base);
    if (MAP_FAILED == base)
	perror("mmap");
    
    exit(0);
}


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