101 lines
3.5 KiB
C
101 lines
3.5 KiB
C
/****************************************************************************
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* sched/task/task_getppid.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <sys/types.h>
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#include <unistd.h>
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#include <sched.h>
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#include <errno.h>
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#include "sched/sched.h"
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#include "task/task.h"
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: getppid
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*
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* Description:
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* Get the parent task ID of the currently executing task.
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*
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* Input parameters:
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* None
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*
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* Returned Value:
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* Normally when called from user applications, getppid() will return the
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* parent task ID of the currently executing task, that is, the task at the
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* head of the ready-to-run list. There is no specification for any errors
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* returned from getppid().
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*
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* getppid(), however, may be called from within the OS in some cases.
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* There are certain situations during context switching when the OS data
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* structures are in flux and where the current task at the head of the
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* ready-to-run task list is not actually running. In that case,
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* getppid() will return the error: -ESRCH
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*
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****************************************************************************/
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pid_t getppid(void)
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{
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FAR struct tcb_s *rtcb;
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/* Get the TCB at the head of the ready-to-run task list. That
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* will usually be the currently executing task. There is are two
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* exceptions to this:
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*
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* 1. Early in the start-up sequence, the ready-to-run list may be
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* empty! In this case, of course, the CPU0 start-up/IDLE thread with
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* pid == 0 must be running, and
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* 2. As described above, during certain context-switching conditions the
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* task at the head of the ready-to-run list may not actually be
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* running.
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*/
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rtcb = this_task();
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if (rtcb != NULL)
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{
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/* Check if the task is actually running */
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if (rtcb->task_state == TSTATE_TASK_RUNNING)
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{
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/* Yes.. Return the parent task ID from the TCB at the head of the
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* ready-to-run task list
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*/
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return rtcb->group->tg_ppid;
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}
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/* No.. return -ESRCH to indicate this condition */
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return (pid_t)-ESRCH;
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}
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/* We must have been called earlier in the start up sequence from the
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* start-up/IDLE thread before the ready-to-run list has been initialized.
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*/
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return IDLE_PROCESS_ID;
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}
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