Context
Table of Contents
1 Context handling
The context variable is a handle for the state of the library,
and is stored in a data structure which can't be seen outside of
the library. To simplify compatibility with other languages, the
pointer to the internal data structure is converted into a 64-bit
signed integer, defined in the qmckl_context type.
A value of QMCKL_NULL_CONTEXT for the context is equivalent to a
NULL pointer.
typedef int64_t qmckl_context ; #define QMCKL_NULL_CONTEXT (qmckl_context) 0
An immutable context would have required to implement a garbage collector. To keep the library simple, we have chosen to implement the context as a mutable data structure, so it has to be handled with care.
By convention, in this file context is a qmckl_context variable
and ctx is a qmckl_context_struct* pointer.
1.1 Data structure
The qmcklextra pointer lets the other implementation of the library add specific things to the context. For example a GPU implementation of QMCkl will need to store the device ID in the context, and this can be made by creating a private data structure containing all GPU-specific data, including the device ID.
A tag is used internally to check if the memory domain pointed by a pointer is a valid context. This allows to check that even if the pointer associated with a context is non-null, we can still verify that it points to the expected data structure.
The qmckl_context_check function checks if the domain pointed by
the pointer is a valid context. It returns the input qmckl_context
if the context is valid, QMCKL_NULL_CONTEXT otherwise.
qmckl_context qmckl_context_check (const qmckl_context context) ;
The context keeps a date that allows to check which data needs to be recomputed. The date is incremented when the context is touched.
When a new element is added to the context, the functions
qmckl_context_create qmckl_context_destroy and qmckl_context_copy
should be updated in order to make deep copies.
When the electron coordinates have changed, the context is touched using the following function.
qmckl_exit_code qmckl_context_touch (const qmckl_context context);
This has the effect to increment the date of the context.
1.2 Creation
To create a new context, qmckl_context_create() should be used.
- Upon success, it returns a pointer to a new context with the
qmckl_contexttype - It returns
QMCKL_NULL_CONTEXTupon failure to allocate the internal data structure - A new context always has all its members initialized with a NULL value
qmckl_context qmckl_context_create();
1.3 Locking
For thread safety, the context may be locked/unlocked. The lock is
initialized with the PTHREAD_MUTEX_RECURSIVE attribute, and the
number of times the thread has locked it is saved in the
lock_count attribute.
void qmckl_lock (qmckl_context context); void qmckl_unlock(qmckl_context context);
1.4 TODO Copy
qmckl_context_copy makes a deep copy of a context. It returns
QMCKL_NULL_CONTEXT upon failure.
1.5 Destroy
The context is destroyed with qmckl_context_destroy, leaving the ancestors untouched.
It frees the context, and returns the previous context.
qmckl_exit_code qmckl_context_destroy (const qmckl_context context);