started to implement endpoint to fetch task backtraces (#38)

Title should be self-explanatory.

Extends the debug super-endpoint `/debug_engine` to handle task backtraces and also adds a `/task_backtraces` endpoint to collect task backtraces on-demand.

README.md

@@ -29,6 +29,10 @@ Julia process to interrogate its performance characteristics.
 - `/heap_snapshot` endpoint to take a heap snapshot with `Profile.take_heap_snapshot`.
     - Default query params: `/heap_snapshot?all_one=false`
 
+**Task Backtraces**
+- `/task_backtraces` endpoint to collect task backtraces. Only available in Julia v1.10+.
+    - Default query params: none.
+
 ## Examples
 
 Start the server on your production process
@@ -80,3 +84,11 @@ $ curl '127.0.0.1:16825/heap_snapshot?all_one=false' --output prof1.heapsnapshot
 
 And upload it in the [Chrome DevTools snapshot viewer](https://developer.chrome.com/docs/devtools/memory-problems/heap-snapshots/#view_snapshots) to explore the heap.
 In Chrome `View > Developer > Developer Tools`, select the `Memory` tab, and press the `Load` button to upload the file.
+
+### Task Backtraces
+
+Collect task backtraces (requires Julia v1.10+):
+```bash
+$ curl '127.0.0.1:16825/task_backtraces' --output task_backtraces.txt
+```
+

src/ProfileEndpoints.jl

@@ -289,6 +289,34 @@ end
 
 end  # if isdefined
 
+###
+### Task backtraces
+###
+
+function task_backtraces_endpoint(req::HTTP.Request)
+    @static if VERSION < v"1.10.0-DEV.0"
+        return HTTP.Response(501, "Task backtraces are only available in Julia 1.10+")
+    end
+    return handle_task_backtraces()
+end
+
+function handle_task_backtraces(stage_path = nothing)
+    @info "Starting Task Backtrace Profiling from ProfileEndpoints"
+    @static if VERSION < v"1.10.0-DEV.0"
+        return HTTP.Response(501, "Task backtraces are only available in Julia 1.10+")
+    end
+    if stage_path === nothing
+        stage_path = tempdir()
+    end
+    backtrace_file = joinpath(stage_path, "task_backtraces.txt")
+    open(backtrace_file, "w") do io
+        redirect_stderr(io) do
+            ccall(:jl_print_task_backtraces, Cvoid, ())
+        end
+    end
+    return HTTP.Response(200, backtrace_file)
+end
+
 ###
 ### Debug super-endpoint
 ###
@@ -330,6 +358,8 @@ function debug_profile_endpoint_with_stage_path(stage_path = nothing)
                 parse(Bool, get(body, "pprof", default_pprof())),
                 stage_path
             )
+        elseif profile_type == "task_backtraces"
+            return handle_task_backtraces(stage_path)
         else
             return HTTP.Response(400, "Unknown profile_type: $profile_type")
         end
@@ -350,6 +380,7 @@ function register_endpoints(router; stage_path = nothing)
     HTTP.register!(router, "/allocs_profile", allocations_profile_endpoint)
     HTTP.register!(router, "/allocs_profile_start", allocations_start_endpoint)
     HTTP.register!(router, "/allocs_profile_stop", allocations_stop_endpoint)
+    HTTP.register!(router, "/task_backtraces", task_backtraces_endpoint)
     debug_profile_endpoint = debug_profile_endpoint_with_stage_path(stage_path)
     HTTP.register!(router, "/debug_engine", debug_profile_endpoint)
 end

test/runtests.jl

@@ -122,6 +122,18 @@ const url = "http://127.0.0.1:$port"
             @info "filename: $fname"
             @test isfile(fname)
         end
+
+        @testset "Debug endpoint task backtraces" begin
+            @static if VERSION >= v"1.10.0-DEV.0"
+                headers = ["Content-Type" => "application/json"]
+                payload = JSON3.write(Dict("profile_type" => "task_backtraces"))
+                req = HTTP.post("$url/debug_engine", headers, payload)
+                @test req.status == 200
+                fname = read(IOBuffer(req.body), String)
+                @info "filename: $fname"
+                @test isfile(fname)
+            end
+        end
     end
 
     @testset "Heap snapshot $query" for query in ("", "?all_one=true")
@@ -203,6 +215,20 @@ const url = "http://127.0.0.1:$port"
         end
     end
 
+    @testset "task backtraces" begin
+        @testset "task_backtraces endpoint" begin
+            @static if VERSION >= v"1.10.0-DEV.0"
+                req = HTTP.get("$url/task_backtraces", retry=false, status_exception=false)
+                @test req.status == 200
+                @test length(req.body) > 0
+
+                # Test whether the profile returned a valid file
+                data = read(IOBuffer(req.body), String)
+                @test isfile(data)
+            end
+        end
+    end
+
     @testset "error handling" begin
         let res = HTTP.get("$url/profile", status_exception=false)
             @test 400 <= res.status < 500