On Aug 7, 2009, at 12:06, Tim Murison wrote:
The code is below and was compiled with objc-gc-only. If I run the
program,
despite the setMaxConcurrentOperationCount:4, it will use 65
threads. Also
it will leak memory at ~1Mb/sec.
#import <Cocoa/Cocoa.h>
#include <libkern/OSAtomic.h>
volatile int64_t globalCounter;
@interface Operation : NSOperation
+ (Operation*) operation;
@end
@implementation Operation
+ (Operation*) operation
{
return [[Operation alloc] init];
}
- (void) main
{
OSAtomicIncrement64(&globalCounter);
}
@end
int main(int argc, char **argv)
{
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
[queue setMaxConcurrentOperationCount:4];
while (1) {
int64_t tmp;
[queue addOperation:[Operation operation]];
tmp = globalCounter;
if (tmp % 100 == 0) {
[[NSGarbageCollector defaultCollector]
collectExhaustively];
printf("Counter: %lld\n", tmp);
}
}
}
'setMaxConcurrentOperationCount' specifies the number of concurrently
executing threads. I don't see anything in the documentation that
guarantees it will control the number of concurrently existing
threads. Threads may exist waiting to execute, and threads will exist
for some period of time after they finish execution (in the
NSOperation sense of isExecuting, in all cases).
Also, because globalCounter is being changed by the operations,
there's no guarantee the main thread will ever see tmp%100==0, if
you're unlucky, so that collectExhaustively thing is unreliable.
Also, because you're putting the main thread in a hard loop, you're
stealing CPU time that might be used for operations and/or the garbage
collector. Your main thread and your operations are all asking for
100% of the CPU cores they're running in, which is going to make it
hard for the garbage collector to get the compute time it needs.
All in all, it makes me want to ask what you're trying to achieve by
this. To prove that you can outrun the collector? You can.
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