From 0221ebc9b1460230d11407ea747b6bca99d67271 Mon Sep 17 00:00:00 2001
From: Sukera <Seelengrab@users.noreply.github.com>
Date: Sat, 6 Apr 2024 09:28:22 +0200
Subject: [PATCH 1/3] Throw `ConcurrencyViolationError` on `yield` & `throwto`
 with `current_task`

Previously, this errored with a nasty type assert *somewhere*
in the runtime. Throwing a proper `ConcurrencyViolationError`
allows this to be debugged, and makes the error condition known.
---
 base/task.jl | 10 ++++++++--
 test/misc.jl |  3 +++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/base/task.jl b/base/task.jl
index 90f74441c7fbd..f469ddd7b39c7 100644
--- a/base/task.jl
+++ b/base/task.jl
@@ -1040,11 +1040,15 @@ end
 
 A fast, unfair-scheduling version of `schedule(t, arg); yield()` which
 immediately yields to `t` before calling the scheduler.
+
+Throws a `ConcurrencyViolationError` if `t` is the currently running task.
 """
 function yield(t::Task, @nospecialize(x=nothing))
-    (t._state === task_state_runnable && t.queue === nothing) || error("yield: Task not runnable")
+    current = current_task()
+    t === current && throw(ConcurrencyViolationError("Cannot yield to currently running task!"))
+    (t._state === task_state_runnable && t.queue === nothing) || throw(ConcurrencyViolationError("yield: Task not runnable"))
     t.result = x
-    enq_work(current_task())
+    enq_work(current)
     set_next_task(t)
     return try_yieldto(ensure_rescheduled)
 end
@@ -1091,6 +1095,8 @@ end
 
 # yield to a task, throwing an exception in it
 function throwto(t::Task, @nospecialize exc)
+    current = current_task()
+    t === current && throw(ConcurrencyViolationError("Cannot throw an exception to the currently running task!"))
     t.result = exc
     t._isexception = true
     set_next_task(t)
diff --git a/test/misc.jl b/test/misc.jl
index e870c7f491c13..e20b581941857 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -253,6 +253,9 @@ end
 
 @test_throws ErrorException("deadlock detected: cannot wait on current task") wait(current_task())
 
+@test_throws ConcurrencyViolationError("Cannot yield to currently running task!") yield(current_task())
+@test_throws ConcurrencyViolationError("Cannot throw an exception to the currently running task!") throwto(current_task(), ArgumentError())
+
 # issue #41347
 let t = @async 1
     wait(t)

From 6280d38e0cbf708a9041ab11f166d1c9bbc4082c Mon Sep 17 00:00:00 2001
From: Sukera <Seelengrab@users.noreply.github.com>
Date: Sat, 6 Apr 2024 12:01:15 +0200
Subject: [PATCH 2/3] Check that the correct error is thrown

---
 test/misc.jl | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/test/misc.jl b/test/misc.jl
index e20b581941857..aeca80fc1f2aa 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -254,12 +254,12 @@ end
 @test_throws ErrorException("deadlock detected: cannot wait on current task") wait(current_task())
 
 @test_throws ConcurrencyViolationError("Cannot yield to currently running task!") yield(current_task())
-@test_throws ConcurrencyViolationError("Cannot throw an exception to the currently running task!") throwto(current_task(), ArgumentError())
+@test_throws ConcurrencyViolationError("Cannot throw an exception to the currently running task!") Base.throwto(current_task(), ArgumentError())
 
 # issue #41347
 let t = @async 1
     wait(t)
-    @test_throws ErrorException yield(t)
+    @test_throws ConcurrencyViolationError yield(t)
 end
 
 let t = @async error(42)

From 41d026beafd303bea592e89b688e417139b20571 Mon Sep 17 00:00:00 2001
From: Sukera <Seelengrab@users.noreply.github.com>
Date: Sat, 6 Apr 2024 14:36:38 +0200
Subject: [PATCH 3/3] Remove incorrect throw in `throwto`

---
 base/task.jl | 2 --
 test/misc.jl | 1 -
 2 files changed, 3 deletions(-)

diff --git a/base/task.jl b/base/task.jl
index f469ddd7b39c7..653153478108e 100644
--- a/base/task.jl
+++ b/base/task.jl
@@ -1095,8 +1095,6 @@ end
 
 # yield to a task, throwing an exception in it
 function throwto(t::Task, @nospecialize exc)
-    current = current_task()
-    t === current && throw(ConcurrencyViolationError("Cannot throw an exception to the currently running task!"))
     t.result = exc
     t._isexception = true
     set_next_task(t)
diff --git a/test/misc.jl b/test/misc.jl
index aeca80fc1f2aa..4a09015b0dc88 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -254,7 +254,6 @@ end
 @test_throws ErrorException("deadlock detected: cannot wait on current task") wait(current_task())
 
 @test_throws ConcurrencyViolationError("Cannot yield to currently running task!") yield(current_task())
-@test_throws ConcurrencyViolationError("Cannot throw an exception to the currently running task!") Base.throwto(current_task(), ArgumentError())
 
 # issue #41347
 let t = @async 1