_tx_byte_allocate
_tx_byte_allocate用于内存分配，内存分配原理参考上篇博文:Threadx 内存管理-内存字节池
UINT _tx_byte_allocate(TX_BYTE_POOL *pool_ptr, VOID **memory_ptr,
ULONG memory_size, ULONG wait_option)
{
TX_INTERRUPT_SAVE_AREA
REG_1 UINT status; /* Return status */
REG_2 TX_THREAD *thread_ptr; /* Working thread pointer */
REG_3 CHAR_PTR work_ptr; /* Working byte pointer */
/* Pickup the thread pointer. */
#def 临时记录申请内存分配的当前线程
thread_ptr = _tx_thread_current_ptr;
/* Round the memory size up to the next size that is evenly divisible by
an ULONG. This guarantees proper alignment. */
#def 计算申请内存大小，ULONG大小对齐
memory_size = ((memory_size + sizeof(ULONG) - 1) / sizeof(ULONG)) * sizeof(ULONG);
/* Disable interrupts. */
#def 禁止中断，防止打断下面操作
TX_DISABLE
/* Loop to handle cases where the owner of the pool changed. */
#def 循环操作
do
{
/* Indicate that this thread is the current owner. */
#def 先标记内存池拥有者为当前线程
pool_ptr -> tx_byte_pool_owner = thread_ptr;
/* Restore interrupts. */
#def 恢复中断，后面操作可能被高优先级打断，而高优先级线程也可能在这个内存池申请分配内存
TX_RESTORE
/* At this point, the executing thread owns the pool and can perform a search
for free memory. */
work_ptr = _tx_byte_pool_search(pool_ptr, memory_size);
/* Lockout interrupts. */
TX_DISABLE
}
#def 如果申请失败，并且内存池拥有者不在是thread_ptr线程，说明被搞优先级线程抢占，并且在这个内存池申请分配内存；这个线程恢复后，循环继续，再次尝试内存申请
while ((!work_ptr) && (pool_ptr -> tx_byte_pool_owner != thread_ptr));
/* Determine if memory was found. */
#def 申请到了内存，函数返回成功
if (work_ptr)
{
/* Copy the pointer into the return destination. */
*memory_ptr = (VOID *) work_ptr;
/* Set the status to success. */
status = TX_SUCCESS;
}
else
{
#def 内存不够，申请失败，如果wait_option不为0，挂起线程到tx_byte_pool_suspension_list，后面
#def 其它线程释放内存后，在_tx_byte_release中重新申请内存，恢复线程
/* No memory of sufficient size was found... */
/* Determine if the request specifies suspension. */
if (wait_option)
{
#def 挂起线程
/* Prepare for suspension of this thread. */
/* Setup cleanup routine pointer. */
thread_ptr -> tx_suspend_cleanup = _tx_byte_pool_cleanup;
/* Setup cleanup information, i.e. this pool control
block. */
#def 记录内存池管理结构指针
thread_ptr -> tx_suspend_control_block = (VOID_PTR) pool_ptr;
/* Save the return memory pointer address as well. */
#def 记录应用程序传递的用来保存申请到的内存起始地址指针
thread_ptr -> tx_additional_suspend_info = (VOID_PTR) memory_ptr;
/* Save the byte size requested. */
#def 记录需要申请分配内存大小
thread_ptr -> tx_suspend_info = memory_size;
/* Setup suspension list. */
#def 挂起到tx_byte_pool_suspension_list线程，按照fifo，并没有按照优先级高低顺序
if (pool_ptr -> tx_byte_pool_suspension_list)
{
/* This list is not NULL, add current thread to the end. */
thread_ptr -> tx_suspended_next =
pool_ptr -> tx_byte_pool_suspension_list;
thread_ptr -> tx_suspended_previous =
(pool_ptr -> tx_byte_pool_suspension_list) -> tx_suspended_previous;
((pool_ptr -> tx_byte_pool_suspension_list) -> tx_suspended_previous) -> tx_suspended_next =
thread_ptr;
(pool_ptr -> tx_byte_pool_suspension_list) -> tx_suspended_previous = thread_ptr;
}
else
{
/* No other threads are suspended. Setup the head pointer and
just setup this threads pointers to itself. */
pool_ptr -> tx_byte_pool_suspension_list = thread_ptr;
thread_ptr -> tx_suspended_next = thread_ptr;
thread_ptr -> tx_suspended_previous = thread_ptr;
}
/* Increment the suspended thread count. */
pool_ptr -> tx_byte_pool_suspended_count++;
/* Set the state to suspended. */
thread_ptr -> tx_state = TX_BYTE_MEMORY;
/* Set the suspending flag. */
thread_ptr -> tx_suspending = TX_TRUE;
/* Temporarily disable preemption. */
_tx_thread_preempt_disable++;
/* Save the timeout value. */
thread_ptr -> tx_thread_timer.tx_remaining_ticks = wait_option;
/* Restore interrupts. */
TX_RESTORE
/* See if we need to start a timer. */
#def 不等于TX_WAIT_FOREVER，开启定时器，定时器超时会清除申请内存相关操作，并返回申请失败
if (wait_option != TX_WAIT_FOREVER)
{
/* A timeout is required. */
/* Activate the thread timer for the timeout. */
_tx_timer_activate(&(thread_ptr -> tx_thread_timer));
}
/* Call actual thread suspension routine. */
_tx_thread_suspend(thread_ptr);
/* Return the completion status. */
#def 线程恢复后，从这里返回，tx_suspend_status在_tx_byte_release或_tx_byte_pool_cleanup中设置
return (thread_ptr -> tx_suspend_status);
}
else
{
/* Immediate return, return error completion. */
status = TX_NO_MEMORY;
}
}
/* Restore interrupts. */
TX_RESTORE
/* Return completion status. */
return (status);
}