Fixing prematurely freed objects
View Patent ↗A method and mechanism for managing dynamically allocated memory. Portions of memory which are available for allocation have additional information stored in association with each portion which indicates whether the portion has been previously identified as being prematurely freed. In addition, a checksum is stored with each portion of memory. In response to a request for deallocation of a portion of memory, the portion of memory is not deallocated if it is identified as having been prematurely freed. Otherwise, the a checksum is calculated for the portion and it is freed. In response to an allocation request, a candidate portion of memory is identified for allocation and a checksum is calculated for the candidate portion. If the calculated checksum does not match a checksum previously stored for the candidate portion, the portion is identified as having been prematurely freed and is not returned for allocation.
1. A method for managing memory, said method comprising:
detecting a request to free a first block of memory;
freeing said first block of memory, in response to detecting said request and determining said first block of memory does not correspond to a prematurely freed block of memory; and
not freeing said first block of memory, in response to detecting said request and determining said first block of memory corresponds to a prematurely freed block of memory;
in response to identifying the first block corresponds to a prematurely freed block of memory:
storing an indication that the candidate block corresponds to a prematurely freed block of memory;
skipping said first block for purposes of allocation; and
searching for a new block for allocation.
2. The method as recited in claim 1 , wherein in response to determining said block of memory does not correspond to a prematurely freed block of memory, the method further comprises:
calculating a checksum corresponding to said block; and
storing said checksum in association with said block.
3. The method as recited in claim 2 , further comprising:
detecting a request for an allocation of a block of memory;
identifying a candidate block of memory for allocation;
calculating a checksum of said candidate block and comparing the calculated checksum to a previously stored checksum which is associated with the candidate block;
allocating the candidate block, in response to detecting the calculated checksum matches the previously stored checksum; and
identifying the candidate block as corresponding to a prematurely freed block of memory, in response to detecting the calculated checksum does not match the stored checksum.
4. The method as recited in claim 1 , further comprising maintaining a list which identifies requesters of memory allocation which are deemed unsafe.
5. The method as recited in claim 4 , wherein the list identifies the requesters by a program counter corresponding the requester instruction in the program code.
6. The method as recited in claim 5 , wherein freeing said first block of memory is in further response to determining the first block of memory does not correspond to a requestor which is included in the list.
7. The method as recited in claim 6 , wherein in response to detecting the request for an allocation of a block of memory and identifying the candidate block as corresponding to a prematurely freed block of memory, the method further comprises storing an identification of the requester in association with the candidate block and adding the identification to the list.
8. A computing system comprising:
a memory configured to store data; and
a processing device configured to:
detect a request to free a first block of memory;
determine whether said first block of memory corresponds to a prematurely freed block of memory;
free said first block of memory, in response to detecting said request and determining said first block of memory does not correspond to a prematurely freed block of memory; and
not free said first block of memory, in response to detecting said request and determining said first block of memory corresponds to a prematurely freed block of memory;
in response to identifying the first block corresponds to a prematurely freed block of memory:
store an indication that the first block corresponds to a prematurely freed block of memory;
skip said first block for purposes of allocation; and
search for a new block for allocation.
9. The computing system as recited in claim 8 , wherein in response to determining said block of memory does not correspond to a prematurely freed block of memory, the processing device is further configured to:
calculate a checksum corresponding to said block; and
store said checksum in association with said block.
10. The computing system as recited in claim 9 , wherein the processing device is further configured to:
detect a request for an allocation of a block of memory;
identify a candidate block of memory for allocation;
calculate a checksum of said candidate block and comparing the calculated checksum to a previously stored checksum which is associated with the candidate block;
allocate the candidate block, in response to detecting the calculated checksum matches the previously stored checksum; and
identify the candidate block as corresponding to a prematurely freed block of memory, in response to detecting the calculated checksum does not match the stored checksum.
11. The computing system as recited in claim 8 , wherein the processing device is further configured to maintain a list which identifies requestors of memory allocation which are deemed unsafe.
12. The computing system as recited in claim 11 , wherein the list identifies the requesters by a program counter corresponding the requestor instruction in the program code.
13. The computing system as recited in claim 12 , wherein freeing said first block of memory is in further response to determining the first block of memory does not correspond to a requester which is included in the list.
14. The computing system as recited in claim 13 , wherein in response to detecting the request for an allocation of a block of memory and identifying the candidate block as corresponding to a prematurely freed block of memory, the processing device is further configured to store an identification of the requester in association with the candidate block and add the identification to the list.
15. A computer storage medium comprising program instructions for use in monitoring memory usage in an application, wherein the program instructions are computer-executable to:
detect a request to free a first block of memory;
free said first block of memory, in response to detecting said request and determining said first block of memory does not correspond to a prematurely freed block of memory; and
not free said first block of memory, in response to detecting said request and determining said first block of memory corresponds to a prematurely freed block of memory;
in response to identifying the candidate block corresponds to a prematurely freed block of memory, the program instructions are further executable to:
store an indication that the candidate block corresponds to a prematurely freed block of memory;
skip said candidate block for purposes of allocation; and
search for a new candidate block for allocation.
16. The computer storage medium as recited in claim 15 , wherein in response to determining said block of memory does not correspond to a prematurely freed block of memory, the program instructions are further executable to:
calculate a checksum corresponding to said block; and
store said checksum in association with said block.
17. The computer storage medium as recited in claim 16 , wherein the program instructions are further executable to:
detect a request for an allocation of a block of memory;
identify a candidate block of memory for allocation;
calculate a checksum of said candidate block and comparing the calculated checksum to a previously stored checksum which is associated with the candidate block;
allocate the candidate block, in response to detecting the calculated checksum matches the previously stored checksum; and
identify the candidate block as corresponding to a prematurely freed block of memory, in response to detecting the calculated checksum does not match the stored checksum.
18. The computer storage medium as recited in claim 15 , the program instructions are further executable to maintain a list which identifies requesters of memory allocation which are deemed unsafe.