https://gcc.gnu.org/g:0d119fb79e884c9ee5e1ccbbb98311780f92413d
commit r15-673-g0d119fb79e884c9ee5e1ccbbb98311780f92413d
Author: Ronan Desplanques <desplanq...@adacore.com>
Date: Mon Mar 25 14:36:56 2024 +0100
ada: Tweak handling of thread ID on POSIX
This patch changes the task initialization subprograms on POSIX
platforms so that the thread ID of an ATCB is only set once.
This has the advantage of getting rid of the Atomic aspect on
the corresponding record component, and silences a Helgrind
warning about a data race.
gcc/ada/
* libgnarl/s-taprop__linux.adb (Enter_Task): Move setting
of thread ID out of Enter_Task.
(Initialize): Set thread ID for the environment task.
(Create_Task): Remove now unnecessary Unrestricted_Access
attribute and add justification for a memory write.
* libgnarl/s-taprop__posix.adb: Likewise.
* libgnarl/s-taprop__qnx.adb: Likewise.
* libgnarl/s-taprop__rtems.adb: Likewise.
* libgnarl/s-taprop__solaris.adb: Likewise.
* libgnarl/s-taspri__posix.ads: Remove pragma Atomic for
Private_Data.Thread, and update documentation comment.
* libgnarl/s-taspri__lynxos.ads: Likewise.
* libgnarl/s-taspri__posix-noaltstack.ads: Likewise.
* libgnarl/s-taspri__solaris.ads: Likewise.
* libgnarl/s-tporft.adb (Register_Foreign_Thread): Adapt to
Enter_Task not setting the thread ID anymore.
* libgnarl/s-tassta.adb (Task_Wrapper): Update comment.
Diff:
---
gcc/ada/libgnarl/s-taprop__linux.adb | 14 +++++++-------
gcc/ada/libgnarl/s-taprop__posix.adb | 14 +++++++-------
gcc/ada/libgnarl/s-taprop__qnx.adb | 14 +++++++-------
gcc/ada/libgnarl/s-taprop__rtems.adb | 14 +++++++-------
gcc/ada/libgnarl/s-taprop__solaris.adb | 16 ++++++++--------
gcc/ada/libgnarl/s-taspri__lynxos.ads | 16 ++++++++++------
gcc/ada/libgnarl/s-taspri__posix-noaltstack.ads | 16 ++++++++++------
gcc/ada/libgnarl/s-taspri__posix.ads | 16 ++++++++++------
gcc/ada/libgnarl/s-taspri__solaris.ads | 16 ++++++++++------
gcc/ada/libgnarl/s-tassta.adb | 2 +-
gcc/ada/libgnarl/s-tporft.adb | 1 +
11 files changed, 78 insertions(+), 61 deletions(-)
diff --git a/gcc/ada/libgnarl/s-taprop__linux.adb
b/gcc/ada/libgnarl/s-taprop__linux.adb
index 0c09817739ce..0a51b3601c07 100644
--- a/gcc/ada/libgnarl/s-taprop__linux.adb
+++ b/gcc/ada/libgnarl/s-taprop__linux.adb
@@ -730,7 +730,6 @@ package body System.Task_Primitives.Operations is
raise Invalid_CPU_Number;
end if;
- Self_ID.Common.LL.Thread := pthread_self;
Self_ID.Common.LL.LWP := lwp_self;
-- Set thread name to ease debugging. If the name of the task is
@@ -1004,14 +1003,14 @@ package body System.Task_Primitives.Operations is
-- do not need to manipulate caller's signal mask at this point.
-- All tasks in RTS will have All_Tasks_Mask initially.
- -- Note: the use of Unrestricted_Access in the following call is needed
- -- because otherwise we have an error of getting a access-to-volatile
- -- value which points to a non-volatile object. But in this case it is
- -- safe to do this, since we know we have no problems with aliasing and
- -- Unrestricted_Access bypasses this check.
+ -- The write to T.Common.LL.Thread is not racy with regard to the
+ -- created thread because the created thread will not access it until
+ -- we release the RTS lock (or the current task's lock when
+ -- Restricted.Stages is used). One can verify that by inspecting the
+ -- Task_Wrapper procedures.
Result := pthread_create
- (T.Common.LL.Thread'Unrestricted_Access,
+ (T.Common.LL.Thread'Access,
Thread_Attr'Access,
Thread_Body_Access (Wrapper),
To_Address (T));
@@ -1385,6 +1384,7 @@ package body System.Task_Primitives.Operations is
begin
Environment_Task_Id := Environment_Task;
+ Environment_Task.Common.LL.Thread := pthread_self;
Interrupt_Management.Initialize;
diff --git a/gcc/ada/libgnarl/s-taprop__posix.adb
b/gcc/ada/libgnarl/s-taprop__posix.adb
index 7ed52ea2d821..fb70aaf4976e 100644
--- a/gcc/ada/libgnarl/s-taprop__posix.adb
+++ b/gcc/ada/libgnarl/s-taprop__posix.adb
@@ -636,7 +636,6 @@ package body System.Task_Primitives.Operations is
procedure Enter_Task (Self_ID : Task_Id) is
begin
- Self_ID.Common.LL.Thread := pthread_self;
Self_ID.Common.LL.LWP := lwp_self;
Specific.Set (Self_ID);
@@ -841,14 +840,14 @@ package body System.Task_Primitives.Operations is
-- do not need to manipulate caller's signal mask at this point.
-- All tasks in RTS will have All_Tasks_Mask initially.
- -- Note: the use of Unrestricted_Access in the following call is needed
- -- because otherwise we have an error of getting a access-to-volatile
- -- value which points to a non-volatile object. But in this case it is
- -- safe to do this, since we know we have no problems with aliasing and
- -- Unrestricted_Access bypasses this check.
+ -- The write to T.Common.LL.Thread is not racy with regard to the
+ -- created thread because the created thread will not access it until
+ -- we release the RTS lock (or the current task's lock when
+ -- Restricted.Stages is used). One can verify that by inspecting the
+ -- Task_Wrapper procedures.
Result := pthread_create
- (T.Common.LL.Thread'Unrestricted_Access,
+ (T.Common.LL.Thread'Access,
Attributes'Access,
Thread_Body_Access (Wrapper),
To_Address (T));
@@ -1260,6 +1259,7 @@ package body System.Task_Primitives.Operations is
begin
Environment_Task_Id := Environment_Task;
+ Environment_Task.Common.LL.Thread := pthread_self;
Interrupt_Management.Initialize;
diff --git a/gcc/ada/libgnarl/s-taprop__qnx.adb
b/gcc/ada/libgnarl/s-taprop__qnx.adb
index 108180d06176..f475c05c562a 100644
--- a/gcc/ada/libgnarl/s-taprop__qnx.adb
+++ b/gcc/ada/libgnarl/s-taprop__qnx.adb
@@ -654,7 +654,6 @@ package body System.Task_Primitives.Operations is
procedure Enter_Task (Self_ID : Task_Id) is
begin
- Self_ID.Common.LL.Thread := pthread_self;
Self_ID.Common.LL.LWP := lwp_self;
Specific.Set (Self_ID);
@@ -846,14 +845,14 @@ package body System.Task_Primitives.Operations is
-- do not need to manipulate caller's signal mask at this point.
-- All tasks in RTS will have All_Tasks_Mask initially.
- -- Note: the use of Unrestricted_Access in the following call is needed
- -- because otherwise we have an error of getting a access-to-volatile
- -- value which points to a non-volatile object. But in this case it is
- -- safe to do this, since we know we have no problems with aliasing and
- -- Unrestricted_Access bypasses this check.
+ -- The write to T.Common.LL.Thread is not racy with regard to the
+ -- created thread because the created thread will not access it until
+ -- we release the RTS lock (or the current task's lock when
+ -- Restricted.Stages is used). One can verify that by inspecting the
+ -- Task_Wrapper procedures.
Result := pthread_create
- (T.Common.LL.Thread'Unrestricted_Access,
+ (T.Common.LL.Thread'Access,
Attributes'Access,
Thread_Body_Access (Wrapper),
To_Address (T));
@@ -1261,6 +1260,7 @@ package body System.Task_Primitives.Operations is
begin
Environment_Task_Id := Environment_Task;
+ Environment_Task.Common.LL.Thread := pthread_self;
Interrupt_Management.Initialize;
diff --git a/gcc/ada/libgnarl/s-taprop__rtems.adb
b/gcc/ada/libgnarl/s-taprop__rtems.adb
index 3feafd8bc3a3..ea8422cb4543 100644
--- a/gcc/ada/libgnarl/s-taprop__rtems.adb
+++ b/gcc/ada/libgnarl/s-taprop__rtems.adb
@@ -646,7 +646,6 @@ package body System.Task_Primitives.Operations is
procedure Enter_Task (Self_ID : Task_Id) is
begin
- Self_ID.Common.LL.Thread := pthread_self;
Self_ID.Common.LL.LWP := lwp_self;
Specific.Set (Self_ID);
@@ -851,14 +850,14 @@ package body System.Task_Primitives.Operations is
-- do not need to manipulate caller's signal mask at this point.
-- All tasks in RTS will have All_Tasks_Mask initially.
- -- Note: the use of Unrestricted_Access in the following call is needed
- -- because otherwise we have an error of getting a access-to-volatile
- -- value which points to a non-volatile object. But in this case it is
- -- safe to do this, since we know we have no problems with aliasing and
- -- Unrestricted_Access bypasses this check.
+ -- The write to T.Common.LL.Thread is not racy with regard to the
+ -- created thread because the created thread will not access it until
+ -- we release the RTS lock (or the current task's lock when
+ -- Restricted.Stages is used). One can verify that by inspecting the
+ -- Task_Wrapper procedures.
Result := pthread_create
- (T.Common.LL.Thread'Unrestricted_Access,
+ (T.Common.LL.Thread'Access,
Attributes'Access,
Thread_Body_Access (Wrapper),
To_Address (T));
@@ -1270,6 +1269,7 @@ package body System.Task_Primitives.Operations is
begin
Environment_Task_Id := Environment_Task;
+ Environment_Task.Common.LL.Thread := pthread_self;
Interrupt_Management.Initialize;
diff --git a/gcc/ada/libgnarl/s-taprop__solaris.adb
b/gcc/ada/libgnarl/s-taprop__solaris.adb
index 82e51b8d25c5..09f90e6e204e 100644
--- a/gcc/ada/libgnarl/s-taprop__solaris.adb
+++ b/gcc/ada/libgnarl/s-taprop__solaris.adb
@@ -424,6 +424,7 @@ package body System.Task_Primitives.Operations is
begin
Environment_Task_Id := Environment_Task;
+ Self_ID.Common.LL.Thread := thr_self;
Interrupt_Management.Initialize;
@@ -868,8 +869,7 @@ package body System.Task_Primitives.Operations is
procedure Enter_Task (Self_ID : Task_Id) is
begin
- Self_ID.Common.LL.Thread := thr_self;
- Self_ID.Common.LL.LWP := lwp_self;
+ Self_ID.Common.LL.LWP := lwp_self;
Set_Task_Affinity (Self_ID);
Specific.Set (Self_ID);
@@ -997,11 +997,11 @@ package body System.Task_Primitives.Operations is
Opts := THR_DETACHED + THR_BOUND;
end if;
- -- Note: the use of Unrestricted_Access in the following call is needed
- -- because otherwise we have an error of getting a access-to-volatile
- -- value which points to a non-volatile object. But in this case it is
- -- safe to do this, since we know we have no problems with aliasing and
- -- Unrestricted_Access bypasses this check.
+ -- The write to T.Common.LL.Thread is not racy with regard to the
+ -- created thread because the created thread will not access it until
+ -- we release the RTS lock (or the current task's lock when
+ -- Restricted.Stages is used). One can verify that by inspecting the
+ -- Task_Wrapper procedures.
Result :=
thr_create
@@ -1010,7 +1010,7 @@ package body System.Task_Primitives.Operations is
Thread_Body_Access (Wrapper),
To_Address (T),
Opts,
- T.Common.LL.Thread'Unrestricted_Access);
+ T.Common.LL.Thread'Access);
Succeeded := Result = 0;
pragma Assert
diff --git a/gcc/ada/libgnarl/s-taspri__lynxos.ads
b/gcc/ada/libgnarl/s-taspri__lynxos.ads
index a3307000c80a..f5e434eada62 100644
--- a/gcc/ada/libgnarl/s-taspri__lynxos.ads
+++ b/gcc/ada/libgnarl/s-taspri__lynxos.ads
@@ -86,12 +86,16 @@ private
type Private_Data is limited record
Thread : aliased System.OS_Interface.pthread_t;
- pragma Atomic (Thread);
- -- Thread field may be updated by two different threads of control.
- -- (See, Enter_Task and Create_Task in s-taprop.adb). They put the same
- -- value (thr_self value). We do not want to use lock on those
- -- operations and the only thing we have to make sure is that they are
- -- updated in atomic fashion.
+ -- This component is written to once before concurrent access to it is
+ -- possible, and then remains constant. The place where it is written to
+ -- depends on how the enclosing ATCB comes into existence:
+ --
+ -- 1. For the environment task, the component is set in
+ -- System.Task_Primitive.Operations.Initialize.
+ -- 2. For foreign threads, it happens in
+ -- System.Task_Primitives.Operations.Register_Foreign_Thread.
+ -- 3. For others tasks, it's in
+ -- System.Task_Primitives.Operations.Create_Task.
LWP : aliased System.OS_Interface.pthread_t;
-- The purpose of this field is to provide a better tasking support on
diff --git a/gcc/ada/libgnarl/s-taspri__posix-noaltstack.ads
b/gcc/ada/libgnarl/s-taspri__posix-noaltstack.ads
index b92f1dd4ab2d..fb7e07d10cd3 100644
--- a/gcc/ada/libgnarl/s-taspri__posix-noaltstack.ads
+++ b/gcc/ada/libgnarl/s-taspri__posix-noaltstack.ads
@@ -89,12 +89,16 @@ private
type Private_Data is limited record
Thread : aliased System.OS_Interface.pthread_t;
- pragma Atomic (Thread);
- -- Thread field may be updated by two different threads of control.
- -- (See, Enter_Task and Create_Task in s-taprop.adb). They put the same
- -- value (thr_self value). We do not want to use lock on those
- -- operations and the only thing we have to make sure is that they are
- -- updated in atomic fashion.
+ -- This component is written to once before concurrent access to it is
+ -- possible, and then remains constant. The place where it is written to
+ -- depends on how the enclosing ATCB comes into existence:
+ --
+ -- 1. For the environment task, the component is set in
+ -- System.Task_Primitive.Operations.Initialize.
+ -- 2. For foreign threads, it happens in
+ -- System.Task_Primitives.Operations.Register_Foreign_Thread.
+ -- 3. For others tasks, it's in
+ -- System.Task_Primitives.Operations.Create_Task.
LWP : aliased System.Address;
-- The purpose of this field is to provide a better tasking support on
diff --git a/gcc/ada/libgnarl/s-taspri__posix.ads
b/gcc/ada/libgnarl/s-taspri__posix.ads
index 4d0b379556d8..3453f4fea4ce 100644
--- a/gcc/ada/libgnarl/s-taspri__posix.ads
+++ b/gcc/ada/libgnarl/s-taspri__posix.ads
@@ -88,12 +88,16 @@ private
type Private_Data is limited record
Thread : aliased System.OS_Interface.pthread_t;
- pragma Atomic (Thread);
- -- Thread field may be updated by two different threads of control.
- -- (See, Enter_Task and Create_Task in s-taprop.adb). They put the same
- -- value (thr_self value). We do not want to use lock on those
- -- operations and the only thing we have to make sure is that they are
- -- updated in atomic fashion.
+ -- This component is written to once before concurrent access to it is
+ -- possible, and then remains constant. The place where it is written to
+ -- depends on how the enclosing ATCB comes into existence:
+ --
+ -- 1. For the environment task, the component is set in
+ -- System.Task_Primitive.Operations.Initialize.
+ -- 2. For foreign threads, it happens in
+ -- System.Task_Primitives.Operations.Register_Foreign_Thread.
+ -- 3. For others tasks, it's in
+ -- System.Task_Primitives.Operations.Create_Task.
LWP : aliased System.Address;
-- The purpose of this field is to provide a better tasking support on
diff --git a/gcc/ada/libgnarl/s-taspri__solaris.ads
b/gcc/ada/libgnarl/s-taspri__solaris.ads
index 16fc4196b005..586c971dce66 100644
--- a/gcc/ada/libgnarl/s-taspri__solaris.ads
+++ b/gcc/ada/libgnarl/s-taspri__solaris.ads
@@ -95,12 +95,16 @@ private
type Private_Data is limited record
Thread : aliased System.OS_Interface.thread_t;
- pragma Atomic (Thread);
- -- Thread field may be updated by two different threads of control.
- -- (See, Enter_Task and Create_Task in s-taprop.adb). They put the same
- -- value (thr_self value). We do not want to use lock on those
- -- operations and the only thing we have to make sure is that they are
- -- updated in atomic fashion.
+ -- This component is written to once before concurrent access to it is
+ -- possible, and then remains constant. The place where it is written to
+ -- depends on how the enclosing ATCB comes into existence:
+ --
+ -- 1. For the environment task, the component is set in
+ -- System.Task_Primitive.Operations.Initialize.
+ -- 2. For foreign threads, it happens in
+ -- System.Task_Primitives.Operations.Register_Foreign_Thread.
+ -- 3. For others tasks, it's in
+ -- System.Task_Primitives.Operations.Create_Task.
LWP : System.OS_Interface.lwpid_t;
-- The LWP id of the thread. Set by self in Enter_Task
diff --git a/gcc/ada/libgnarl/s-tassta.adb b/gcc/ada/libgnarl/s-tassta.adb
index 01c94b950bae..594a16728666 100644
--- a/gcc/ada/libgnarl/s-tassta.adb
+++ b/gcc/ada/libgnarl/s-tassta.adb
@@ -1079,7 +1079,7 @@ package body System.Tasking.Stages is
Stack_Guard (Self_ID, True);
-- Initialize low-level TCB components, that cannot be initialized by
- -- the creator. Enter_Task sets Self_ID.LL.Thread.
+ -- the creator.
Enter_Task (Self_ID);
diff --git a/gcc/ada/libgnarl/s-tporft.adb b/gcc/ada/libgnarl/s-tporft.adb
index a7b4ce5e29a2..66a9f02656e8 100644
--- a/gcc/ada/libgnarl/s-tporft.adb
+++ b/gcc/ada/libgnarl/s-tporft.adb
@@ -98,6 +98,7 @@ begin
System.Soft_Links.Create_TSD
(Self_Id.Common.Compiler_Data, null, Sec_Stack_Size);
+ Self_Id.Common.LL.Thread := Thread;
Enter_Task (Self_Id);
return Self_Id;
