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simgrid

Msg_file_get_data in SimGrid

I open file by SimGrid framework:

msg_file_t file = MSG_file_open("/scratch/bin/tesh", NULL);
XBT_INFO("file size is %zd", MSG_file_get_size(file));

It's OK:

[carl:host:(1) 0.000000] [remote_io/INFO] file size is 356434

Then I want to set some data to this file. Firstly, I create typedef structure:

typedef struct {
    char* number_used;
}data, *dataPtr;

Then I set data with MSG_file_set_data to this file:

dataPtr data_1 = xbt_new(data, 1);
data_1->number_used = xbt_strdup("1");
MSG_file_set_data(file, data);

But after closing file I can't get the value of data_1->number_used:

file = MSG_file_open("/scratch/bin/tesh", NULL);
dataPtr data_2 = MSG_file_get_data(file);
XBT_INFO("number used %s", data_2->number_used);

It gives segmentation fault and value of data_2 is null. What did I do wrong?

Solution

  • A msg_file_t object only exists between the MSG_file_open and MSG_file_close calls. Calling again MSG_file_open on the same file name creates a new msg_file_t object (a new descriptor). Then user data attached to a msg_file_t are not persistent across multiple open/close on a file name.