Dynamically allocating multiple big arrays in C
I'm writing a program in C on windows that launches 30 threads, each of which needs an array of int16_t.
The size is calculated before the thread function is called and in the example I'm working with it's around 250 millions. This is around 15GB, which should not be a problem, because I have 128GB ram available.
I've tried using both malloc and calloc inside the thread function, but over half of the allocations return NULL with errno set to 12 (enomem).
With a small number of threads (up to 3) it works fine though, same if I just use 1 thread and allocating an unreasonably big array.
My next attempt to solve this issue was to create an array of pointers in the main, allocate the arrays there and pass them as argument to the thread, same thing happened.
So from these results my best guess would be it can't allocate contiguous blocks of memory of that size, so I also tried allocating many smaller arrays, which obviously didn't work either. Is this an expected behaviour or am I doing something wrong?
c arrays windows malloc
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
asked Nov 22 '18 at 15:29
incantationincantation
815
|
show 4 more comments
I'm writing a program in C on windows that launches 30 threads, each of which needs an array of int16_t.
The size is calculated before the thread function is called and in the example I'm working with it's around 250 millions. This is around 15GB, which should not be a problem, because I have 128GB ram available.
I've tried using both malloc and calloc inside the thread function, but over half of the allocations return NULL with errno set to 12 (enomem).
With a small number of threads (up to 3) it works fine though, same if I just use 1 thread and allocating an unreasonably big array.
My next attempt to solve this issue was to create an array of pointers in the main, allocate the arrays there and pass them as argument to the thread, same thing happened.
So from these results my best guess would be it can't allocate contiguous blocks of memory of that size, so I also tried allocating many smaller arrays, which obviously didn't work either. Is this an expected behaviour or am I doing something wrong?
c arrays windows malloc
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
asked Nov 22 '18 at 15:29
incantationincantation
815
2 * 250 * 10^6 * 30 = 15*10^9 bytes. Sanity check your spec before you start coding away maybe.
– Lundin
Nov 22 '18 at 15:33
guess I should've mentioned I have 128 gb of ram available
– incantation
Nov 22 '18 at 15:37
2
I guess what you are actually asking is this: stackoverflow.com/questions/11891593/…
– Lundin
Nov 22 '18 at 15:42
Also a Minimal, Complete, and Verifiable example might help. Just the part that does the failing creation of the array of pointers inmain.
– Jabberwocky
Nov 22 '18 at 15:44
1
Are you compiling as 32 bit or 64 bit code? A 32 bit process cannot address more than 4 GB of memory, even if your computer has 128Gb or ram.
– Jabberwocky
Nov 22 '18 at 15:48
|
show 4 more comments
I'm writing a program in C on windows that launches 30 threads, each of which needs an array of int16_t.
The size is calculated before the thread function is called and in the example I'm working with it's around 250 millions. This is around 15GB, which should not be a problem, because I have 128GB ram available.
I've tried using both malloc and calloc inside the thread function, but over half of the allocations return NULL with errno set to 12 (enomem).
With a small number of threads (up to 3) it works fine though, same if I just use 1 thread and allocating an unreasonably big array.
My next attempt to solve this issue was to create an array of pointers in the main, allocate the arrays there and pass them as argument to the thread, same thing happened.
So from these results my best guess would be it can't allocate contiguous blocks of memory of that size, so I also tried allocating many smaller arrays, which obviously didn't work either. Is this an expected behaviour or am I doing something wrong?
c arrays windows malloc
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
asked Nov 22 '18 at 15:29
incantationincantation
815
I'm writing a program in C on windows that launches 30 threads, each of which needs an array of int16_t.
The size is calculated before the thread function is called and in the example I'm working with it's around 250 millions. This is around 15GB, which should not be a problem, because I have 128GB ram available.
I've tried using both malloc and calloc inside the thread function, but over half of the allocations return NULL with errno set to 12 (enomem).
With a small number of threads (up to 3) it works fine though, same if I just use 1 thread and allocating an unreasonably big array.
My next attempt to solve this issue was to create an array of pointers in the main, allocate the arrays there and pass them as argument to the thread, same thing happened.
So from these results my best guess would be it can't allocate contiguous blocks of memory of that size, so I also tried allocating many smaller arrays, which obviously didn't work either. Is this an expected behaviour or am I doing something wrong?
c arrays windows malloc
c arrays windows malloc
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
asked Nov 22 '18 at 15:29
incantationincantation
815
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
asked Nov 22 '18 at 15:29
incantationincantation
815
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
edited Nov 22 '18 at 16:06
Ring Ø
21.7k45283
21.7k45283
asked Nov 22 '18 at 15:29
incantationincantation
815
asked Nov 22 '18 at 15:29
incantationincantation
815
asked Nov 22 '18 at 15:29
incantationincantation
815
815
2 * 250 * 10^6 * 30 = 15*10^9 bytes. Sanity check your spec before you start coding away maybe.
– Lundin
Nov 22 '18 at 15:33
guess I should've mentioned I have 128 gb of ram available
– incantation
Nov 22 '18 at 15:37
2
I guess what you are actually asking is this: stackoverflow.com/questions/11891593/…
– Lundin
Nov 22 '18 at 15:42
Also a Minimal, Complete, and Verifiable example might help. Just the part that does the failing creation of the array of pointers inmain.
– Jabberwocky
Nov 22 '18 at 15:44
1
Are you compiling as 32 bit or 64 bit code? A 32 bit process cannot address more than 4 GB of memory, even if your computer has 128Gb or ram.
– Jabberwocky
Nov 22 '18 at 15:48
|
show 4 more comments
2 * 250 * 10^6 * 30 = 15*10^9 bytes. Sanity check your spec before you start coding away maybe.
– Lundin
Nov 22 '18 at 15:33
guess I should've mentioned I have 128 gb of ram available
– incantation
Nov 22 '18 at 15:37
2
I guess what you are actually asking is this: stackoverflow.com/questions/11891593/…
– Lundin
Nov 22 '18 at 15:42
Also a Minimal, Complete, and Verifiable example might help. Just the part that does the failing creation of the array of pointers inmain.
– Jabberwocky
Nov 22 '18 at 15:44
1
Are you compiling as 32 bit or 64 bit code? A 32 bit process cannot address more than 4 GB of memory, even if your computer has 128Gb or ram.
– Jabberwocky
Nov 22 '18 at 15:48
2 * 250 * 10^6 * 30 = 15*10^9 bytes. Sanity check your spec before you start coding away maybe.
– Lundin
Nov 22 '18 at 15:33
2 * 250 * 10^6 * 30 = 15*10^9 bytes. Sanity check your spec before you start coding away maybe.
– Lundin
Nov 22 '18 at 15:33
guess I should've mentioned I have 128 gb of ram available
– incantation
Nov 22 '18 at 15:37
guess I should've mentioned I have 128 gb of ram available
– incantation
Nov 22 '18 at 15:37
2
2
I guess what you are actually asking is this: stackoverflow.com/questions/11891593/…
– Lundin
Nov 22 '18 at 15:42
I guess what you are actually asking is this: stackoverflow.com/questions/11891593/…
– Lundin
Nov 22 '18 at 15:42
Also a Minimal, Complete, and Verifiable example might help. Just the part that does the failing creation of the array of pointers in
main.– Jabberwocky
Nov 22 '18 at 15:44
Also a Minimal, Complete, and Verifiable example might help. Just the part that does the failing creation of the array of pointers in
main.– Jabberwocky
Nov 22 '18 at 15:44
1
1
Are you compiling as 32 bit or 64 bit code? A 32 bit process cannot address more than 4 GB of memory, even if your computer has 128Gb or ram.
– Jabberwocky
Nov 22 '18 at 15:48
Are you compiling as 32 bit or 64 bit code? A 32 bit process cannot address more than 4 GB of memory, even if your computer has 128Gb or ram.
– Jabberwocky
Nov 22 '18 at 15:48
|
show 4 more comments
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2 * 250 * 10^6 * 30 = 15*10^9 bytes. Sanity check your spec before you start coding away maybe.
– Lundin
Nov 22 '18 at 15:33
guess I should've mentioned I have 128 gb of ram available
– incantation
Nov 22 '18 at 15:37
2
I guess what you are actually asking is this: stackoverflow.com/questions/11891593/…
– Lundin
Nov 22 '18 at 15:42
Also a Minimal, Complete, and Verifiable example might help. Just the part that does the failing creation of the array of pointers in
main.– Jabberwocky
Nov 22 '18 at 15:44
1
Are you compiling as 32 bit or 64 bit code? A 32 bit process cannot address more than 4 GB of memory, even if your computer has 128Gb or ram.
– Jabberwocky
Nov 22 '18 at 15:48