|Copyright||(c) The University of Glasgow 2001|
|License||BSD-style (see the file libraries/base/LICENSE)|
Memory-related system things.
Allocation counter and limits
Every thread has an allocation counter that tracks how much
memory has been allocated by the thread. The counter is
initialized to zero, and
setAllocationCounter sets the current
value. The allocation counter counts *down*, so in the absence of
a call to
setAllocationCounter its value is the negation of the
number of bytes of memory allocated by the thread.
There are two things that you can do with this counter:
- Use it as a simple profiling mechanism, with
- Use it as a resource limit. See
Allocation accounting is accurate only to about 4Kbytes.
Return the current value of the allocation counter for the current thread.
Enables the allocation counter to be treated as a limit for the
current thread. When the allocation limit is enabled, if the
allocation counter counts down below zero, the thread will be sent
AllocationLimitExceeded asynchronous exception. When this
happens, the counter is reinitialised (by default
to 100K, but tunable with the
+RTS -xq option) so that it can handle
the exception and perform any necessary clean up. If it exhausts
this additional allowance, another
is sent, and so forth. Like other asynchronous exceptions, the
AllocationLimitExceeded exception is deferred while the thread is inside
mask or an exception handler in
Note that memory allocation is unrelated to live memory, also known as heap residency. A thread can allocate a large amount of memory and retain anything between none and all of it. It is better to think of the allocation limit as a limit on CPU time, rather than a limit on memory.
Compared to using timeouts, allocation limits don't count time spent blocked or in foreign calls.