diff options
Diffstat (limited to 'gcc/ada/s-taskin.ads')
| -rw-r--r-- | gcc/ada/s-taskin.ads | 55 |
1 files changed, 27 insertions, 28 deletions
diff --git a/gcc/ada/s-taskin.ads b/gcc/ada/s-taskin.ads index 0e08ffd3981..8e5616bf85f 100644 --- a/gcc/ada/s-taskin.ads +++ b/gcc/ada/s-taskin.ads @@ -55,21 +55,21 @@ with Unchecked_Conversion; package System.Tasking is - -- ------------------- - -- -- Locking Rules -- - -- ------------------- - -- + ------------------- + -- Locking Rules -- + ------------------- + -- The following rules must be followed at all times, to prevent -- deadlock and generally ensure correct operation of locking. - -- + -- . Never lock a lock unless abort is deferred. - -- + -- . Never undefer abort while holding a lock. - -- + -- . Overlapping critical sections must be properly nested, -- and locks must be released in LIFO order. -- e.g., the following is not allowed: - -- + -- Lock (X); -- ... -- Lock (Y); @@ -77,31 +77,31 @@ package System.Tasking is -- Unlock (X); -- ... -- Unlock (Y); - -- + -- Locks with lower (smaller) level number cannot be locked -- while holding a lock with a higher level number. (The level -- number is the number at the left.) - -- + -- 1. System.Tasking.PO_Simple.Protection.L (any PO lock) -- 2. System.Tasking.Initialization.Global_Task_Lock (in body) -- 3. System.Task_Primitives.Operations.Single_RTS_Lock -- 4. System.Tasking.Ada_Task_Control_Block.LL.L (any TCB lock) - -- + -- Clearly, there can be no circular chain of hold-and-wait -- relationships involving locks in different ordering levels. - -- + -- We used to have Global_Task_Lock before Protection.L but this was -- clearly wrong since there can be calls to "new" inside protected -- operations. The new ordering prevents these failures. - -- + -- Sometimes we need to hold two ATCB locks at the same time. To allow -- us to order the locking, each ATCB is given a unique serial -- number. If one needs to hold locks on several ATCBs at once, -- the locks with lower serial numbers must be locked first. - -- + -- We don't always need to check the serial numbers, since -- the serial numbers are assigned sequentially, and so: - -- + -- . The parent of a task always has a lower serial number. -- . The activator of a task always has a lower serial number. -- . The environment task has a lower serial number than any other task. @@ -360,25 +360,24 @@ package System.Tasking is -- Some protection is described in terms of tasks related to the -- ATCB being protected. These are: - -- Self: The task which is controlled by this ATCB. - -- Acceptor: A task accepting a call from Self. - -- Caller: A task calling an entry of Self. - -- Parent: The task executing the master on which Self depends. - -- Dependent: A task dependent on Self. - -- Activator: The task that created Self and initiated its activation. - -- Created: A task created and activated by Self. + -- Self: The task which is controlled by this ATCB + -- Acceptor: A task accepting a call from Self + -- Caller: A task calling an entry of Self + -- Parent: The task executing the master on which Self depends + -- Dependent: A task dependent on Self + -- Activator: The task that created Self and initiated its activation + -- Created: A task created and activated by Self -- Note: The order of the fields is important to implement efficiently -- tasking support under gdb. -- Currently gdb relies on the order of the State, Parent, Base_Priority, -- Task_Image, Task_Image_Len, Call and LL fields. - ---------------------------------------------------------------------- - -- Common ATCB section -- - -- -- - -- This section is used by all GNARL implementations (regular and -- - -- restricted) -- - ---------------------------------------------------------------------- + ------------------------- + -- Common ATCB section -- + ------------------------- + + -- Section used by all GNARL implementations (regular and restricted) type Common_ATCB is record State : Task_States; |