process: implement getpid (#30013)

Closes #4752

NEWS.md

@@ -21,6 +21,8 @@ New library functions
 
   * `splitpath(p::String)` function, which is the opposite of `joinpath(parts...)`: it splits a filepath into its components ([#28156]).
   * `isnothing(::Any)` function, to check whether something is a `Nothing`, returns a `Bool` ([#29679]).
+  * `getpid(::Process)` method ([#24064]).
+
 
 Standard library changes
 ------------------------

base/process.jl

@@ -385,6 +385,7 @@ function uv_return_spawn(p::Ptr{Cvoid}, exit_status::Int64, termsignal::Int32)
     proc.exitcode = exit_status
     proc.termsignal = termsignal
     ccall(:jl_close_uv, Cvoid, (Ptr{Cvoid},), proc.handle)
+    proc.handle = C_NULL
     notify(proc.exitnotify)
     nothing
 end
@@ -682,7 +683,7 @@ function test_success(proc::Process)
         #TODO: this codepath is not currently tested
         throw(_UVError("could not start process $(string(proc.cmd))", proc.exitcode))
     end
-    proc.exitcode == 0 && (proc.termsignal == 0 || proc.termsignal == SIGPIPE)
+    return proc.exitcode == 0 && (proc.termsignal == 0 || proc.termsignal == SIGPIPE)
 end
 
 function success(x::Process)
@@ -744,6 +745,20 @@ kill(ps::Vector{Process}) = foreach(kill, ps)
 kill(ps::ProcessChain) = foreach(kill, ps.processes)
 kill(p::Process) = kill(p, SIGTERM)
 
+"""
+    getpid(process) -> Int32
+
+Get the child process ID, if it still exists.
+"""
+function Libc.getpid(p::Process)
+    ppid = Int32(0)
+    if p.handle != C_NULL
+        ppid = ccall(:jl_uv_process_pid, Int32, (Ptr{Cvoid},), p.handle)
+    end
+    ppid <= 0 && throw(_UVError("getpid", UV_ESRCH))
+    return ppid
+end
+
 function _contains_newline(bufptr::Ptr{Cvoid}, len::Int32)
     return (ccall(:memchr, Ptr{Cvoid}, (Ptr{Cvoid},Int32,Csize_t), bufptr, '\n', len) != C_NULL)
 end
@@ -755,7 +770,7 @@ end
 
 Determine whether a process is currently running.
 """
-process_running(s::Process) = s.exitcode == typemin(fieldtype(Process, :exitcode))
+process_running(s::Process) = s.handle != C_NULL
 process_running(s::Vector{Process}) = any(process_running, s)
 process_running(s::ProcessChain) = process_running(s.processes)
 

src/jl_uv.c

@@ -151,9 +151,9 @@ void jl_uv_flush(uv_stream_t *stream)
         return;
     while (uv_is_writable(stream) && stream->write_queue_size != 0) {
         int fired = 0;
-	uv_buf_t buf;
-	buf.base = (char*)(&buf + 1);
-	buf.len = 0;
+        uv_buf_t buf;
+        buf.base = (char*)(&buf + 1);
+        buf.len = 0;
         uv_write_t *write_req = (uv_write_t*)malloc(sizeof(uv_write_t));
         write_req->data = (void*)&fired;
         if (uv_write(write_req, stream, &buf, 1, uv_flush_callback) != 0)
@@ -165,6 +165,7 @@ void jl_uv_flush(uv_stream_t *stream)
 }
 
 // getters and setters
+JL_DLLEXPORT int jl_uv_process_pid(uv_process_t *p) { return p->pid; }
 JL_DLLEXPORT void *jl_uv_process_data(uv_process_t *p) { return p->data; }
 JL_DLLEXPORT void *jl_uv_buf_base(const uv_buf_t *buf) { return buf->base; }
 JL_DLLEXPORT size_t jl_uv_buf_len(const uv_buf_t *buf) { return buf->len; }

test/spawn.jl

@@ -230,10 +230,14 @@ if valgrind_off
 end
 
 # setup_stdio for AbstractPipe
-let out = Pipe(), proc = run(pipeline(`$echocmd "Hello World"`, stdout=IOContext(out,stdout)), wait=false)
+let out = Pipe(),
+    proc = run(pipeline(`$exename --startup-file=no -e 'println(getpid())'`, stdout=IOContext(out, :foo => :bar)), wait=false)
+    # < don't block here before getpid call >
+    pid = getpid(proc)
     close(out.in)
-    @test read(out, String) == "Hello World\n"
+    @test parse(Int32, read(out, String)) === pid > 1
     @test success(proc)
+    @test_throws Base.IOError getpid(proc)
 end
 
 # issue #5904