System.Mem

Memory-related system things.

Garbage collection

performGC :: IO ()

Triggers an immediate major garbage collection.

performMajorGC :: IO ()

Triggers an immediate major garbage collection.

Since: base-4.7.0.0

performMinorGC :: IO ()

Triggers an immediate minor garbage collection.

Since: base-4.7.0.0

Allocation counter and limits

setAllocationCounter :: Int64 -> IO ()

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 getAllocationCounter.
• Use it as a resource limit. See enableAllocationLimit.

Allocation accounting is accurate only to about 4Kbytes.

Since: base-4.8.0.0

getAllocationCounter :: IO Int64

Return the current value of the allocation counter for the current thread.

Since: base-4.8.0.0

enableAllocationLimit :: IO ()

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 the 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 AllocationLimitExceeded exception 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 catch.

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.

Since: base-4.8.0.0

disableAllocationLimit :: IO ()

Disable allocation limit processing for the current thread.

Since: base-4.8.0.0