Calling GetModuleHandle repeatedly

Question

3.00/5 (1 vote)

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I'm wading through some legacy code and came across the following

HANDLE	hDll;

for (;;) {
    hDll = GetModuleHandle("xxx.dll"); // this is in xxx.dll's source
    if (NULL != hDll) {
         break;
    }
}

I really don't see the point of doing this, and MSDN says nothing about calling it repeatedly. Either it succeeds and loops only once, or fails and loops forever.

Is there any scenario where it is required?

Thanks in advance

Posted 21-May-12 22:07pm

Indivara

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Comments

Mohibur Rashid 22-May-12 5:32am

Copied from msdn:
Retrieves a module handle for the specified module. The module must have been loaded by the calling process.
I think:
Probably, it wait for the module to be loaded by the same process. may be some other thread is suppose to load the module

Indivara 22-May-12 9:12am

It is trying to get its own handle, so the thing should definitely be loaded by then.

Mohibur Rashid 22-May-12 22:04pm

if (NULL != hDll) \\this statement is checking that fact whether it is loaded or not. as I said, it can be loaded by different thread

Indivara 23-May-12 18:56pm

You mean if two threads call it simultaneously, only one will succeed?

Mohibur Rashid 23-May-12 20:56pm

take this as example

thread_function(...)
{
while(global_variable);
global_variable=1;
... //rest of code
... //rest of code
global_variable=0;
}

this function will wait to continue until global_variable is set to 0

Mohibur Rashid 23-May-12 21:02pm

oh another thing, if i didn't understand wrong then i think, GetModuleHandle function don't load the dll it just return the loaded dll instance

Indivara 24-May-12 5:35am

Yes, of course, this is *inside* the DLL, so it doesn't get called in the first place unless the DLL itself is loaded.

Indivara 24-May-12 5:34am

Your code misses the point. (BTW global_variable's value is undefined on entry, so it may or may not enter the loop in the first place. I suppose you meant to initialize it before the loop?)

The code I posted has a potential infinite loop, and I was not clear on what MSDN doesn't say...

Mohibur Rashid 24-May-12 5:56am

I thought you would give a little respect to me :),

I didn't miss that point, i dint feel it would be important to tell you. It is already assigned, when main start someone should have to assign it to zero so that thread get executed. if I assign to high value thread would never be executed even for once. if I never assign it it would have garbage value and that value wont be zero, so the thread would never get executed and will be halted for ever. i didn't expect to explain this silly issue :) but no hard feeling.

Indivara 24-May-12 8:41am

You've got the wrong impression, there was no disrespect whatsoever. I was merely stating the fact that your comment didn't answer what I asked. Thanks for taking the time and trouble. I assumed you intended to post the following code

void function()
{
flag = 1; // this is global
while (flag); // this waits for another thread to clear it

// do something here
}

In my case, it is GetModuleHandle's behavior that I was not sure about.

3 solutions

Solution 3

C++

#include<windows.h>
#include<stdio.h>
#include<string.h>

int main(void)
{
	HMODULE module_handle = 0;
	while((module_handle = GetModuleHandle(TEXT("library.dll"))) == 0)
		printf("The specified module could not be found.\n");
	printf("Module handle = %x\n", module_handle);
	return 0;
}

Posted 6-Oct-12 6:08am

ZeusAFK

Updated 6-Oct-12 6:10am

v2

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Richard MacCutchan · Accepted Answer · 2012-05-21T23:28:00

Solution 1

This looks like a very bad idea. Call it once and report failure/success as required. See also the remarks section here[^].

Posted 21-May-12 23:28pm

Richard MacCutchan

Updated 21-May-12 23:30pm

v2

Comments

Indivara 22-May-12 9:15am

That's what I was going to do, but thought there may be some obscure reason for doing this, maybe for some old OS. I really don't want to touch any more than necessary...

Pablo Aliskevicius · Accepted Answer · 2012-05-21T23:30:00

Solution 2

Legacy code is fun... ;)
I'll risk a wild guess: someone once used to call LoadLibrary("some_other_library.dll") on a worker thread, and this loop was meant to wait for the other library to be available.
Then, some other person used copy/paste...
Looks like a case of cargo-cult programming[^]

Just my two bits,

Pablo.

Posted 21-May-12 23:30pm

Pablo Aliskevicius

Comments

Indivara 22-May-12 9:16am

Quite likely. This is from the thousand-liner I mentioned in the Lounge.

Calling GetModuleHandle repeatedly

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