Hi,
I've run into an issue where static initialization/ or constructor
attribute functions that are called in a loaded shared object causes a hang.
All versions I've tried (1.2.4 - eventual release of 2.0.0) hit the same issue.
Here's the scenario (and I've attached sample code to reproduce the issue). The
main code opens a shared object with dlopen, and one of the static
initialization functions does a fork or system command. For
fork/execvp/execvpe/execve, they all have to grab the lock with write
permissions. The problem is that before we call the actual dlopen, we have to
grab the lock with read permissions. Normally we release the lock after dlopen
stuff all finishes. The problem is that we're not done with dlopen, so as a
result the call trying to get the write lock can't get it since there's still a
reader waiting on it. With my particular situation, I can make progress by not
grabbing the lock on the dlopen, since I have well defined times as to when a
checkpoint will occur, but I wanted to bring this to your attention, so you all
can figure out the best way to deal with it.
---------- dlopen_test.c ----------
#include<cstdio>
#include<dlfcn.h>
#include<dmtcpaware.h>
typedef int (*print_fn)(void);
int main() {
printf("Opening ./printer.so\n");
void *so = dlopen("./printer.so", RTLD_LOCAL| RTLD_LAZY);
printf("Done opening ./printer.so\n");
print_fn print_func;
print_func = (print_fn)dlsym(so, "print_func");
print_func();
return 0;
}
---------- printer.c ----------
#include<cstdio>
#include<cstdlib>
extern "C" int
print_constructor() {
printf(" In print_constructor\n");
system("echo ' Will I hang?'"); // This is where in DMTCP environment,
it hangs
printf(" Leaving print_constructor\n");
return 0;
}
extern "C" int
print_func() {
printf(" In print_func\n");
return 0;
}
static int value = print_constructor();
---------- Expected results ----------
Opening ./printer.so
In print_constructor
Will I hang?
Leaving print_constructor
Done opening ./printer.so
In print_func
Joshua Louie
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