Concurrency primitives #1052

phischu · 2025-06-12T14:06:14Z

No description provided.

Copilot

Pull Request Overview

This PR replaces the old promise-based implementation in C and Effekt with a channel-based API, renames the wait function to sleep in the time library, and updates example imports accordingly.

Switch C-side Promise to Channel with states EMPTY, SENDED, WAITED
Rename extern async def wait to sleep in io/time.effekt
Add new io/channel and io/promise Effekt modules and update examples

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
libraries/llvm/io.c	Replaced Promise struct and functions with Channel
libraries/common/io/time.effekt	Renamed `wait` to `sleep` in time API
libraries/common/io/promise.effekt	Added new Effekt promise module
libraries/common/io/channel.effekt	Added new Effekt channel module
libraries/common/io.effekt	Removed old promise code, slimmed imports
examples/stdlib/io/time.effekt	Updated example to use `sleep`
examples/stdlib/io/promise.effekt	Added `import io/promise`
examples/stdlib/io/filesystem/...	Added `import io/promise`
examples/stdlib/acme.effekt	Added `import io/channel` & `io/promise`
examples/benchmarks/.../interleave_promises.effekt	Added `import io/promise`

Comments suppressed due to low confidence (1)

libraries/llvm/io.c:301

The state name 'SENDED' is grammatically incorrect; consider renaming it to 'SENT' to improve clarity.

typedef enum { EMPTY, SENDED, WAITED } channel_state_t;

libraries/llvm/io.c

libraries/common/io/channel.effekt

Copilot · 2025-06-16T14:21:37Z

libraries/llvm/io.c

+void c_channel_send(struct Pos channel, struct Pos value) {
+    Channel* f = (Channel*)channel.obj;
+    switch (f->state) {
+        case EMPTY: {
+            f->state = SENDED;
+            f->payload.value = value;
+            erasePositive(channel);
            break;
-        case RESOLVED:
-            erasePositive(promise);
+        }
+        case SENDED: {
+            erasePositive(channel);
            erasePositive(value);
-            eraseStack(stack);
-            fprintf(stderr, "ERROR: Promise already resolved\n");
+            // TODO more graceful panic
+            fprintf(stderr, "ERROR: Channel already sended\n");
            exit(1);
            break;
+        }
+        case WAITED: {
+            Stack stack = f->payload.stack;
+            f->state = EMPTY;
+            erasePositive(channel);
+            resume_Pos(stack, value);
+            break;
+        }
    }
-    // TODO stack overflow?
-    // We need to erase the promise now, since we consume it.
-    erasePositive(promise);
 }

-void c_promise_await(struct Pos promise, Stack stack) {
-    Promise* p = (Promise*)promise.obj;
-
-    Stack head;
-    Listeners* tail;
-    Listeners* node;
-    struct Pos value;
-
-    switch (p->state) {
-        case UNRESOLVED:
-            head = p->payload.listeners.head;
-            tail = p->payload.listeners.tail;
-            if (head != NULL) {
-                node = (Listeners*)malloc(sizeof(Listeners));
-                node->head = head;
-                node->tail = tail;
-                p->payload.listeners.head = stack;
-                p->payload.listeners.tail = node;
-            } else {
-                p->payload.listeners.head = stack;
-            };
+void c_channel_wait(struct Pos channel, Stack stack) {
+    Channel* f = (Channel*)channel.obj;
+    switch (f->state) {
+        case EMPTY: {
+            f->state = WAITED;
+            f->payload.stack = stack;
+            erasePositive(channel);
            break;
-        case RESOLVED:
-            value = p->payload.value;
-            sharePositive(value);
+        }
+        case SENDED: {
+            struct Pos value = f->payload.value;
+            f->state = EMPTY;
+            erasePositive(channel);
            resume_Pos(stack, value);
            break;
-    };
-    // TODO hmm, stack overflow?
-    erasePositive(promise);
-}
-
-struct Pos c_promise_make() {
-    Promise* promise = (Promise*)malloc(sizeof(Promise));
-
-    promise->rc = 0;
-    promise->eraser = c_promise_erase_listeners;
-    promise->state = UNRESOLVED;
-    promise->payload.listeners.head = NULL;
-    promise->payload.listeners.tail = NULL;
-
-    return (struct Pos) { .tag = 0, .obj = promise, };
+        }
+        case WAITED: {
+            erasePositive(channel);
+            eraseStack(stack);
+            // TODO more graceful panic
+            fprintf(stderr, "ERROR: Channel already waited\n");
+            exit(1);
+            break;
+        }
+    }


There is a TODO for a more graceful panic; consider implementing structured error handling rather than calling exit directly.

This is C and this is an assertion violation.

Copilot · 2025-06-16T14:21:37Z

libraries/llvm/io.c

+        }
+        case SENDED: {
+            struct Pos value = f->payload.value;
+            f->state = EMPTY;


In the SENDED branch of c_channel_wait, erasing the channel after setting its state to EMPTY prevents payload.value from being freed, leading to a memory leak. Consider explicitly erasing the value or adjusting the state before erasing.

Suggested change

f->state = EMPTY;

f->state = EMPTY;

erasePositive(value);

Nono, the value is moved!

phischu requested review from b-studios and removed request for b-studios June 13, 2025 08:33

phischu changed the title ~~Promises in terms of Futures~~ Promises in terms of Channels Jun 13, 2025

phischu force-pushed the concurrency branch 2 times, most recently from 94f661d to 6a24a05 Compare June 13, 2025 08:52

b-studios requested a review from Copilot June 16, 2025 14:19

Copilot AI reviewed Jun 16, 2025

View reviewed changes

jiribenes added area:llvm area:stdlib labels Jul 2, 2025

phischu force-pushed the concurrency branch from 78d8a2a to 73930f1 Compare July 8, 2025 08:01

phischu force-pushed the concurrency branch from 73930f1 to 69137ab Compare July 29, 2025 09:34

phischu changed the title ~~Promises in terms of Channels~~ Promises in terms of Signals Jul 29, 2025

phischu requested review from marvinborner and removed request for marvinborner July 30, 2025 11:22

phischu force-pushed the concurrency branch from 41ccd98 to 3b5db11 Compare August 4, 2025 09:50

phischu requested a review from b-studios August 11, 2025 14:19

phischu changed the title ~~Promises in terms of Signals~~ Concurrency primitives Aug 16, 2025

phischu force-pushed the concurrency branch 3 times, most recently from b383f2a to 6cb85be Compare August 25, 2025 07:05

phischu added 10 commits August 27, 2025 16:48

Futures

7925646

Promises in user space

c8f5133

Fix warnings

8905db5

Fix test

14bf25d

Rename wait to sleep

39bd49a

Delete promises

0db64a9

Fix future reference count

f4c9eb3

Fix other tests

708a816

Add promises to acme

bd4b21f

Fix typo

34202cc

phischu added 12 commits August 27, 2025 16:48

Rename and move futures to channels

7e7d7a1

Fix grammar

637b0ab

Rename Channel to Signal

5aa2196

State after signal happened

ce117fb

Mark low-level primitives as unsafe

4951300

Start considering channels

05a0c9c

Fix multiple receives

c9e6579

Avoid stack overflow by yielding to trampoline

751f4b0

Add to acme

f5b4a7d

Make signals rendezvous

800013e

Further simplify signal code

eb95784

Signal closing by state

a8ef69b

phischu force-pushed the concurrency branch from 6cb85be to a8ef69b Compare August 27, 2025 14:48

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Concurrency primitives #1052

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Concurrency primitives #1052

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Pull Request Overview

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Copilot AI Jun 16, 2025

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