Gbase 8s UDR memory management_ 01_ mi_ alloc

function mi_alloc() The role of is ： Allocate a user memory block of a specified size , And return a pointer to the block .

1. grammar

void *mi_alloc(size)

mi_integer size;

size Number of bytes to allocate .

On the client side LIBMI Valid in application ？	Valid in user-defined routines ？
yes	yes

2. usage

         function mi_alloc() The role of is ： by DataBlade API The number of bytes of user memory allocated by the module .mi_alloc（） Function is the constructor of user memory .

         Server side ： from C From the perspective of user-defined routines , The behavior of this function is similar to malloc（） system call , Only the database server can be recycled mi_alloc（） Allocated memory . The delta function is going to be ： Allocate memory for the current memory duration . By default , The current memory duration is PER_ROUTINE. Use PER_ROUTINE The duration of the , The database server is C UDR Release the allocated memory after returning .

Except callback routines , You can change the memory duration in any of the following ways ：

        1, Use mi_dalloc（） instead of mi_alloc（） To allocate memory .

mi_dalloc（） The function works the same way as mi_alloc（） identical , And provide the option of specifying the duration .

        2, Calling mi_alloc（） Before , First call mi_switch_mem_duration（）.

function mi_switch_mem_duration() Used to change the current memory duration of all subsequent memory allocations .

         stay UDR Routine , When an exception is thrown , The database server is automatically released mi_alloc（） Allocated memory .

         Important note ： stay C UDR in , Use DataBlade API Memory management function to allocate memory . Use DataBlade API The memory management function can ensure that the database server can automatically release memory , Especially in the case of return value or exception , Otherwise, the routine will not be able to free memory .

         client ： On the client side LIBMI In the application ,mi_alloc（） Working mode and malloc（） Exactly the same ： It allocates storage on the heap of the client process . The database server does not perform any automatic storage retrieval . client LIBMI Application must use mi_free（） To explicitly release mi_alloc（） All assignments made . client LIBMI Application ignores memory duration .

client LIBMI Applications can use DataBlade API Memory management function or system memory management function （ Such as malloc（））.

         function mi_alloc() The role of is ： Returns a pointer to the newly allocated user memory . Cast this pointer to match the user-defined buffer or allocated structure .DataBlade API Modules can be used mi_free（） To release the mi_alloc（） Allocated memory （ When the memory is no longer needed ）.

3. Return value

         One void The pointer .

         Pointer to newly allocated memory . Cast this pointer to match the user-defined buffer or structure for which memory is allocated .

        NULL

         Function cannot allocate memory .

        mi_alloc（） The function will not raise... When encountering a runtime error MI_Exception event . therefore , It does not cause callbacks to be called .