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digitalmars.D.learn - Error while trying to allocate memory (malloc)

reply "CrudOMatic" <crudomatic gmail.com> writes:
The following code:

import std.stdio, std.cstream, std.c.stdlib;

private {
	//import rescache.cache;
	//import mm.mempool;
}

void main(string[] args)
{
	// press <Return> before program begins
	din.getc();
	
	memoryPool memPool = new memoryPool(1024);
	writeln("Block Allocated!");
	
	// press <Return> to end program
	din.getc();
	//return cast(int)0;
}

	// Growable/shrinkable memory pool, for speedy memory allocation
	class memoryPool {
		private:
			// Allocation header, count and keep track of allocs and keep 
first, last info
			struct s_allocHeader {
				int m_allocCount; // count number of allocations from pool
				s_allocInfo* p_first; // pointer to first allocation info 
struct
				s_allocInfo* p_last; // pointer to last alloc info struct 
(should be null if only one)
			}
			// Keep track of allocations from the memory pool
			struct s_allocInfo {
				align(4) // align on 4-byte boundaries
				void* p_data; // pointer to data chunk allocated out
				void* p_inBlock; // pointer to block this allocation was made 
in
				int m_dataSize; // size of allocated chunk
				s_allocInfo* p_next; // pointer to next allocation list entry
			}
			
			// Block header, count and keep track of system allocs and 
keep first, last info
			struct s_blockHeader {
				int m_blockCount; // count number of allocations from system
				s_blockInfo* p_first; // pointer to first block info struct
				s_blockInfo* p_last; // pointer to last block info struct 
(should be null if only one)
			}
			// Keep track of block allocations
			struct s_blockInfo {
				align(4) // align on 4-byte boundaries
				void* p_block; // pointer to the memory allocated from the 
system
				int m_blockSize; // size of block allocated from the system
				bool m_poolMember; // whether or not the block was allocated 
for the memory pool
				s_blockInfo* p_next; // pointer to next block list entry
			}
			
			int m_CHUNK_SIZE = 128; // n-byte allocations from the pool
			int m_BLOCK_SIZE = 4096; // pool block size
		
		public:	
			// Allocator
			//void* alloc(int numChunks = 1, bool useMemPool = true) { }
			// Deallocator
			void free() { }
			// Grow the memory pool
			void growPool(int numBlocks = 1) { }
			// Shrink the memory pool
			void shrinkPool(int numBlocks = 1) { }
			
			// Constructor; pass it the initial memory pool size in MB
			this(int initialPoolSize) {
				// set up allocation list
				s_allocHeader* m_allocList;
				// set up block list
				s_blockHeader* m_blockList;
				
				// create initial block info reference, and set block count 
to 1
				m_blockList.p_first = malloc(s_blockInfo.sizeof);
				//m_blockList.m_blockCount = 1;
				// allocate initial block of memory and store it in block 
info reference
				//s_blockInfo* tmp = m_blockList.p_first;
				//tmp.p_block = malloc(cast(size_t)initialPoolSize);
				//tmp.m_blockSize = initialPoolSize;
				//tmp.m_poolMember = true;
				//tmp.p_next = null;
			}
			// Deconstructor
			~this() { }
	} // END of c_memoryPool class

when compiled, gives the error:

Error: cannot implicitly convert expression (malloc(16u)) of type 
void* to s_blockInfo*

on line (75):

m_blockList.p_first = malloc(s_blockInfo.sizeof);

What is going on here?

I even tried using new, but got an Access Violation

Any help would be appreciated.
Aug 06 2012
parent reply "Minas Mina" <minas_mina1990 hotmail.co.uk> writes:
Maybe you need a cast before malloc to convert it to a 
"s_blockInfo*"?
Aug 06 2012
parent reply "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 13:22:08 UTC, Minas Mina wrote:
 Maybe you need a cast before malloc to convert it to a 
 "s_blockInfo*"?

Just did, and compiled. Errored out with (from my IDE):
 (9:54:32 AM) AccessViolation-Exception
 (9:54:32 AM) c0000005
 (9:54:32 AM)  Exception in debugger client (9:54:32 AM) 
 IDebugEventCallbacks::Exception
 (9:54:32 AM)  callback.
 (9:54:32 AM)       PC: (9:54:32 AM) 09239f05
 (9:54:32 AM)   VA: (9:54:32 AM) 00000000
 (9:54:32 AM)   R/W: (9:54:32 AM) 0
 (9:54:32 AM)   Parameter: (9:54:32 AM) 00000000
 (9:54:32 AM) (9:54:32 AM) Program execution halted...

Running it directly gives me: object.Error: Access Violation ---------------- I:\Prog\Projects\D\resource-cache\resource-cache\main.d(13): D main ----------------
Aug 06 2012
parent reply "Eyyub" <eyyub.pangearaion gmail.com> writes:
On Monday, 6 August 2012 at 13:59:35 UTC, CrudOMatic wrote:
 On Monday, 6 August 2012 at 13:22:08 UTC, Minas Mina wrote:
 Maybe you need a cast before malloc to convert it to a 
 "s_blockInfo*"?

Just did, and compiled. Errored out with (from my IDE):
 (9:54:32 AM) AccessViolation-Exception
 (9:54:32 AM) c0000005
 (9:54:32 AM)  Exception in debugger client (9:54:32 AM) 
 IDebugEventCallbacks::Exception
 (9:54:32 AM)  callback.
 (9:54:32 AM)       PC: (9:54:32 AM) 09239f05
 (9:54:32 AM)   VA: (9:54:32 AM) 00000000
 (9:54:32 AM)   R/W: (9:54:32 AM) 0
 (9:54:32 AM)   Parameter: (9:54:32 AM) 00000000
 (9:54:32 AM) (9:54:32 AM) Program execution halted...

Running it directly gives me: object.Error: Access Violation ---------------- I:\Prog\Projects\D\resource-cache\resource-cache\main.d(13): D main ----------------

You get an Access Violation error because `m_blockList` is null.
Aug 06 2012
parent reply "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 14:14:12 UTC, Eyyub wrote:
 On Monday, 6 August 2012 at 13:59:35 UTC, CrudOMatic wrote:
 On Monday, 6 August 2012 at 13:22:08 UTC, Minas Mina wrote:
 Maybe you need a cast before malloc to convert it to a 
 "s_blockInfo*"?

Just did, and compiled. Errored out with (from my IDE):
 (9:54:32 AM) AccessViolation-Exception
 (9:54:32 AM) c0000005
 (9:54:32 AM)  Exception in debugger client (9:54:32 AM) 
 IDebugEventCallbacks::Exception
 (9:54:32 AM)  callback.
 (9:54:32 AM)       PC: (9:54:32 AM) 09239f05
 (9:54:32 AM)   VA: (9:54:32 AM) 00000000
 (9:54:32 AM)   R/W: (9:54:32 AM) 0
 (9:54:32 AM)   Parameter: (9:54:32 AM) 00000000
 (9:54:32 AM) (9:54:32 AM) Program execution halted...

Running it directly gives me: object.Error: Access Violation ---------------- I:\Prog\Projects\D\resource-cache\resource-cache\main.d(13): D main ----------------

You get an Access Violation error because `m_blockList` is null.

So, do I use new or what? In C it was just declare and go...
Aug 06 2012
parent reply "Eyyub" <eyyub.pangearaion gmail.com> writes:
On Monday, 6 August 2012 at 14:55:05 UTC, CrudOMatic wrote:
 In C it was just declare and go...

Really ? I don't think, because : s_blockHeader* m_blockList; Here, m_blockList is a pointer to s_blockHeader struct, and so the default value is `null`. So, trying to access to(?) a struct member whereas the pointer is set to null, is a nonsense. Tell me if I'm wrong. (I did not programming in C since 2 years)
 So, do I use new or what?

I do not know what you're trying to do, but if you want a pointer you can use `new` or `malloc`.(it depends on what you need) May be someone can help you better than me.
Aug 06 2012
parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 8/6/12, Eyyub <eyyub.pangearaion gmail.com> wrote:
 Tell me if I'm wrong. (I did not programming in C since 2 years)

You're not wrong. m_blockList is a pointer and OP needs to allocate an s_blockHeader instance before he uses it: s_blockHeader* m_blockList = cast(s_blockHeader*)malloc(s_blockHeader.sizeof);
Aug 06 2012
next sibling parent "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 15:36:03 UTC, Andrej Mitrovic wrote:
 On 8/6/12, Eyyub <eyyub.pangearaion gmail.com> wrote:
 Tell me if I'm wrong. (I did not programming in C since 2 
 years)

You're not wrong. m_blockList is a pointer and OP needs to allocate an s_blockHeader instance before he uses it: s_blockHeader* m_blockList = cast(s_blockHeader*)malloc(s_blockHeader.sizeof);

oops. Thanks. brainfart I guess, been a while since I've used any C like languages.
Aug 06 2012
prev sibling parent reply "CrudOMatic" <crudomatic gmail.com> writes:
On Monday, 6 August 2012 at 15:36:03 UTC, Andrej Mitrovic wrote:
 On 8/6/12, Eyyub <eyyub.pangearaion gmail.com> wrote:
 Tell me if I'm wrong. (I did not programming in C since 2 
 years)

You're not wrong. m_blockList is a pointer and OP needs to allocate an s_blockHeader instance before he uses it: s_blockHeader* m_blockList = cast(s_blockHeader*)malloc(s_blockHeader.sizeof);

another quick question - are these allocations automatically entered into the GC heap? If so then I can just disable garbage collection?
Aug 06 2012
parent reply Andrej Mitrovic <andrej.mitrovich gmail.com> writes:
On 8/6/12, CrudOMatic <crudomatic gmail.com> wrote:
 another quick question - are these allocations automatically
 entered into the GC heap? If so then I can just disable garbage
 collection?

No, there is the standard C malloc/free in std.c.stdlib which you're using, and then there's the GC.malloc and GC.free in core.memory if you want to allocate from the GC heap.
Aug 06 2012
parent Marco Leise <Marco.Leise gmx.de> writes:
Am Mon, 6 Aug 2012 18:25:01 +0200
schrieb Andrej Mitrovic <andrej.mitrovich gmail.com>:

 On 8/6/12, CrudOMatic <crudomatic gmail.com> wrote:
 another quick question - are these allocations automatically
 entered into the GC heap? If so then I can just disable garbage
 collection?

No, there is the standard C malloc/free in std.c.stdlib which you're using, and then there's the GC.malloc and GC.free in core.memory if you want to allocate from the GC heap.

And in the latter case write: auto m_blockList = new s_blockHeader; -- Marco
Aug 07 2012