6 ms·

I'm no great programmer, so my stupid question of the day is: why do people depend on GC so much? Garbage collection is one of those weird things that everyone

I'm no great programmer, so my stupid question of the day is: why do people depend on GC so much? Garbage collection is one of those weird things that everyone seems to accept must be necessary in higher level languages, and end up being quite a burden in operation. The more people depend on dynamic memory, the more likely GC problems are. Meanwhile, the simplest fix in the world - restart the process frequently - prevents memory leaks from accumulating, and requires no complicated tuning.

stormbrew 7y ago
> Meanwhile, the simplest fix in the world - restart the process frequently - prevents memory leaks from accumulating, and requires no complicated tuning. This is just a degenerate case of garbage collection, really.
- tempguy9999 7y ago
  A novel and valid perspective. I have simply relied on leaking wildly before, knowing it's a small program that will end soon. It's an acceptable solution in some cases.
  - segfaultbuserr 7y ago
    Agree. The best way to manage memory in trivial, one-off C programs is not managing it at all. Don't try to free() everything. When I first started to write in C, I attempted to free() whenever I have a chance to, no matter how trivial the program is. Later a textbook convinced me that the effort is not worthwhile (unless for learning C) if all your program does is some simple calculation or processing.
  - LadyCailin 7y ago
    The JVM now has the epsilon GC, which does basically that, it just never GC’s. It’s unfortunate though that there’s no explicit way to tell java to free up a certain reference, if so, in combination with epsilon, you could write real time programs. Maybe you already can do something like that in the embedded java version though? Not sure.
    - tempguy9999 7y ago
      Interesting. First I've heard of it. Well I guess if you can ensure bounded space by limited allocaton, then simply shove manually 'freed' stuff back on a free list, you could do that, sure. But a quick google gets https://openjdk.java.net/jeps/318 https://openjdk.java.net/jeps/318 which does say Non-Goals It is not a goal to introduce manual memory management features to Java language and/or JVM... but it doesn't say you can't or shouldn't. Game on then.
      - LadyCailin 7y ago
        Sure, if all your objects are mutable, then that can work, but a lot of stuff in core libraries are not, and you can’t control those allocations, short of not using them. There is also sun.misc.Unsafe, which has freeMemory, but first of all, I don’t know if that works for arbitrary addresses, or just ones previously allocated from the allocateMemory method, and anyways, I don’t think there’s a reliable way to get the address of an arbitrary object in the first place. But to add both of those pieces of functionality should be a pretty small patch to the jvm code anyways, so if someone were really motivated, it may not be all that much work anyways.
        tempguy9999 7y ago
        > and you can’t control those allocations You're totally right. Rather stupidly I hadn't thought of that.
segfaultbuserr 7y ago
I've seen many advocates of C++ claim that RAII [0] is a viable alternative paradigm to garbage collection or even a silver bullet to resource management in general. I find it's useful but I don't believe it's a silver bullet, yet my skill level is not high enough to come up with a counterargument, but you may find this approach interesting. [0] https://en.wikipedia.org/wiki/Resource_acquisition_is_initialization https://en.wikipedia.org/wiki/Resource_acquisition_is_initia...
- mrkeen 7y ago
  RAII works as long as you don't have closures, which are prevalent in higher-order/functional settings. If I adhere to RAII, I guarantee that if I allocate something in a scope then it will be de-allocated when I leave the scope. But if I want to return a closure (a function pointer + state) then I can't de-allocate it myself. I thing C++ and Rust are trying to address this kind of thing with move semantics and ownership. Perhaps functional languages will solve this kind of thing with linear types in the future. I'm currently looking into 'defunctionalization', 'lambda lifting', etc. to see if they are viable alternatives.
  - thesz 7y ago
    https://en.wikipedia.org/wiki/Region-based_memory_management#Region_inference https://en.wikipedia.org/wiki/Region-based_memory_management... You can infer where you should allocate data. It was done 25 years ago. The problem is that for complex programs you end with one big region and this is not useful. Linear types that are visible to the user will not solve these problems. In fact, they will complicate things greatly, because you have to provide two functions for mapping, for example: for normal and linear types. And their mix with normal types is problematic at best. The inference of linear operations in the backend, on the other hand, can be more efficient - you may end up using linear memory references not knowing about that.
reikonomusha 7y ago
GC gives you memory safety in practice. It’s not possible to slip up in normal circumstances.
- adrianN 7y ago
  GC and memory safety are orthogonal problems.
cardiffspaceman 7y ago
One of the Lisp machines of the 80's required you to save your work and reload so it would load in its more compact form. This was the first little while until they built the GC for this machine. In a sane program without GC, you'll be freeing the memory when you don't need it any more, and your less talented colleagues will get it wrong.
cjfd 7y ago
Restarting the process frequently sounds like a very messy solution. It is not acceptable in all cases to restart the process frequently. For server software it is the rule that this is not acceptable. Also note that if your software is going to be used more it would need more frequent restarts. This will generally not make users happy. Maybe you could sometimes get away with starting a new process for every login. Memory usage will be higher in that case, though, perhaps unacceptably so. Also for software that is used on the desktop it would generally be frowned upon by the users. I suppose it is possible to avoid garbage collection if you are willing to accept kind of old-style programming practices. You could have arrays of objects and when an object is no longer needed you don't deallocate it but allow it to be reused when another object of that kind is needed. I guess this would not lead to clearer code for most purposes. But, who knows, some people have been complaining about the lack of clarity in object oriented code.
deleted 7y ago
[deleted]
pif 7y ago
I was going to upvote your comment and blame HN for not being able to upvote more than once. Then you ruined it all with the last sentence...
rurban 7y ago
Many reasons: * It's much faster than malloc/free. a fragmented free is much much slower than a full stop-the-world major GC, and GC allocation is zero cost. * it makes your program memory safe, memory safety is too hard to be left to the user. * it makes your program run faster with a compacting collector (but not this trivial one). it does defragmentation, and puts together used arrays/strings, so that they often are on the same cache-line. typically 2x faster.
Impossible 7y ago
I'm not entirely sure why you're being downvoted, at the very least downvotes prove your original point... A lot of console games do this intentionally, and various console SDKs have special reboot modes to support it. It's falling out of favor in support of games that are architected for streaming, but they still kind of do the same thing internally (free a large chunk and start loading a new one from disk). It actually seems like a valid approach for back end services, especially if those services are mostly short lived and have quick start up times. It's a hard thing to do with a lot of the runtimes most web applications arr built with, but might be a valid approach with Rust or Go. I've heard people doing similar things with Erlang/OTP.

stormbrew 7y ago

> Meanwhile, the simplest fix in the world - restart the process frequently - prevents memory leaks from accumulating, and requires no complicated tuning. This is just a degenerate case of garbage collection, really.

tempguy9999 7y ago
A novel and valid perspective. I have simply relied on leaking wildly before, knowing it's a small program that will end soon. It's an acceptable solution in some cases.
- segfaultbuserr 7y ago
  Agree. The best way to manage memory in trivial, one-off C programs is not managing it at all. Don't try to free() everything. When I first started to write in C, I attempted to free() whenever I have a chance to, no matter how trivial the program is. Later a textbook convinced me that the effort is not worthwhile (unless for learning C) if all your program does is some simple calculation or processing.
- LadyCailin 7y ago
  The JVM now has the epsilon GC, which does basically that, it just never GC’s. It’s unfortunate though that there’s no explicit way to tell java to free up a certain reference, if so, in combination with epsilon, you could write real time programs. Maybe you already can do something like that in the embedded java version though? Not sure.
  - tempguy9999 7y ago
    Interesting. First I've heard of it. Well I guess if you can ensure bounded space by limited allocaton, then simply shove manually 'freed' stuff back on a free list, you could do that, sure. But a quick google gets https://openjdk.java.net/jeps/318 https://openjdk.java.net/jeps/318 which does say Non-Goals It is not a goal to introduce manual memory management features to Java language and/or JVM... but it doesn't say you can't or shouldn't. Game on then.
    - LadyCailin 7y ago
      Sure, if all your objects are mutable, then that can work, but a lot of stuff in core libraries are not, and you can’t control those allocations, short of not using them. There is also sun.misc.Unsafe, which has freeMemory, but first of all, I don’t know if that works for arbitrary addresses, or just ones previously allocated from the allocateMemory method, and anyways, I don’t think there’s a reliable way to get the address of an arbitrary object in the first place. But to add both of those pieces of functionality should be a pretty small patch to the jvm code anyways, so if someone were really motivated, it may not be all that much work anyways.
      - tempguy9999 7y ago
        > and you can’t control those allocations You're totally right. Rather stupidly I hadn't thought of that.

segfaultbuserr 7y ago

I've seen many advocates of C++ claim that RAII [0] is a viable alternative paradigm to garbage collection or even a silver bullet to resource management in general. I find it's useful but I don't believe it's a silver bullet, yet my skill level is not high enough to come up with a counterargument, but you may find this approach interesting. [0] https://en.wikipedia.org/wiki/Resource_acquisition_is_initialization https://en.wikipedia.org/wiki/Resource_acquisition_is_initia...

mrkeen 7y ago
RAII works as long as you don't have closures, which are prevalent in higher-order/functional settings. If I adhere to RAII, I guarantee that if I allocate something in a scope then it will be de-allocated when I leave the scope. But if I want to return a closure (a function pointer + state) then I can't de-allocate it myself. I thing C++ and Rust are trying to address this kind of thing with move semantics and ownership. Perhaps functional languages will solve this kind of thing with linear types in the future. I'm currently looking into 'defunctionalization', 'lambda lifting', etc. to see if they are viable alternatives.
- thesz 7y ago
  https://en.wikipedia.org/wiki/Region-based_memory_management#Region_inference https://en.wikipedia.org/wiki/Region-based_memory_management... You can infer where you should allocate data. It was done 25 years ago. The problem is that for complex programs you end with one big region and this is not useful. Linear types that are visible to the user will not solve these problems. In fact, they will complicate things greatly, because you have to provide two functions for mapping, for example: for normal and linear types. And their mix with normal types is problematic at best. The inference of linear operations in the backend, on the other hand, can be more efficient - you may end up using linear memory references not knowing about that.

reikonomusha 7y ago

GC gives you memory safety in practice. It’s not possible to slip up in normal circumstances.

adrianN 7y ago
GC and memory safety are orthogonal problems.

cardiffspaceman 7y ago

One of the Lisp machines of the 80's required you to save your work and reload so it would load in its more compact form. This was the first little while until they built the GC for this machine. In a sane program without GC, you'll be freeing the memory when you don't need it any more, and your less talented colleagues will get it wrong.

cjfd 7y ago

Restarting the process frequently sounds like a very messy solution. It is not acceptable in all cases to restart the process frequently. For server software it is the rule that this is not acceptable. Also note that if your software is going to be used more it would need more frequent restarts. This will generally not make users happy. Maybe you could sometimes get away with starting a new process for every login. Memory usage will be higher in that case, though, perhaps unacceptably so. Also for software that is used on the desktop it would generally be frowned upon by the users. I suppose it is possible to avoid garbage collection if you are willing to accept kind of old-style programming practices. You could have arrays of objects and when an object is no longer needed you don't deallocate it but allow it to be reused when another object of that kind is needed. I guess this would not lead to clearer code for most purposes. But, who knows, some people have been complaining about the lack of clarity in object oriented code.

deleted 7y ago

[deleted]

pif 7y ago

I was going to upvote your comment and blame HN for not being able to upvote more than once. Then you ruined it all with the last sentence...

rurban 7y ago

Many reasons: * It's much faster than malloc/free. a fragmented free is much much slower than a full stop-the-world major GC, and GC allocation is zero cost. * it makes your program memory safe, memory safety is too hard to be left to the user. * it makes your program run faster with a compacting collector (but not this trivial one). it does defragmentation, and puts together used arrays/strings, so that they often are on the same cache-line. typically 2x faster.

Impossible 7y ago

I'm not entirely sure why you're being downvoted, at the very least downvotes prove your original point... A lot of console games do this intentionally, and various console SDKs have special reboot modes to support it. It's falling out of favor in support of games that are architected for streaming, but they still kind of do the same thing internally (free a large chunk and start loading a new one from disk). It actually seems like a valid approach for back end services, especially if those services are mostly short lived and have quick start up times. It's a hard thing to do with a lot of the runtimes most web applications arr built with, but might be a valid approach with Rust or Go. I've heard people doing similar things with Erlang/OTP.