2 files changed, 174 insertions, 0 deletions
diff --git a/libptimc/libptimc.c b/libptimc/libptimc.c
new file mode 100644
index 0000000..3cda04b
--- /dev/null
+++ b/libptimc/libptimc.c
@@ -0,0 +1,125 @@
+#include "libptimc.h"
+
+static struct imcthread **THREADS = 0;
+static size_t N_THREADS = 0;
+static struct imcthread *CURRENT_THREAD = 0;
+static ucontext_t MASTER_CTX;
+
+static void switch_to_thread(struct imcthread *thread);
+static void imcthread_entry_point(int tid);
+
+static void resetter() {
+    for (int i = 0; i < N_THREADS; i++) {
+        free(THREADS[i]->ctx.uc_stack.ss_sp);
+        free(THREADS[i]);
+    }
+    free(THREADS);
+    THREADS = 0;
+    N_THREADS = 0;
+    CURRENT_THREAD = 0;
+}
+
+int imcthread_create(imcthread_t *threadp,
+                     imcthread_attr_t *attr,
+                     void *(*start_routine)(void *),
+                     void *arg) {
+    assert(!attr);
+    THREADS = realloc(THREADS, (++N_THREADS) * sizeof(THREADS[0]));
+    THREADS[N_THREADS - 1] = calloc(1, sizeof(struct imcthread));
+
+    struct imcthread *thread = THREADS[N_THREADS - 1];
+    *threadp = thread;
+    thread->fn = start_routine;
+    thread->arg = arg;
+    thread->state = THREAD_STATE_FETUS;
+    thread->id = N_THREADS - 1;
+
+    assert(!getcontext(&thread->ctx));
+    thread->ctx.uc_stack.ss_size = 4 * 1024 * 1024;
+    thread->ctx.uc_stack.ss_sp = malloc(thread->ctx.uc_stack.ss_size);
+    thread->ctx.uc_link = 0;
+    makecontext(&thread->ctx, imcthread_entry_point, 1, thread->id);
+
+    return 0;
+}
+
+int imcthread_yieldh(hash_t hash) {
+    // pauses the current thread and returns to the master thread
+    assert(CURRENT_THREAD);
+    struct imcthread *thread = CURRENT_THREAD;
+
+    if (thread->state == THREAD_STATE_DEAD) {
+        for (size_t i = 0; i < N_THREADS; i++)
+            if (THREADS[i]->waiting_on == thread)
+                THREADS[i]->waiting_on = 0;
+    }
+
+    CURRENT_THREAD = 0;
+    swapcontext(&(thread->ctx), &MASTER_CTX);
+
+    return 0;
+}
+int imcthread_yield(void) { imcthread_yieldh(0); }
+
+static void *_imc_check_main(void *_) { imc_check_main(); return 0; }
+void check_main() {
+    register_resetter(resetter);
+
+    imcthread_t _thread;
+    imcthread_create(&_thread, NULL, _imc_check_main, NULL);
+
+    while (1) {
+        int n_alive = 0, n_avail = 0;
+        for (int i = 0; i < N_THREADS; i++) {
+            if (THREADS[i]->state == THREAD_STATE_DEAD) continue;
+            n_alive++;
+            if (THREADS[i]->waiting_on) continue;
+            n_avail++;
+        }
+        // check that we're not in a deadlock
+        if (!n_avail) { assert(!n_alive); break; }
+
+        int count = choose(n_avail, 0);
+        for (int i = 0; i < N_THREADS; i++) {
+            if (THREADS[i]->state == THREAD_STATE_DEAD) continue;
+            if (THREADS[i]->waiting_on) continue;
+            if (count--) continue;
+            switch_to_thread(THREADS[i]);
+            break;
+        }
+    }
+}
+
+int imcthread_joinh(imcthread_t thread, void **retval, hash_t hash) {
+    if (thread->state != THREAD_STATE_DEAD) {
+        CURRENT_THREAD->waiting_on = thread;
+        imcthread_yield();
+    }
+
+    if (retval) *retval = thread->retval;
+    return 0;
+}
+int imcthread_join(imcthread_t thread, void **retval) {
+    return imcthread_joinh(thread, retval, 0);
+}
+
+static void switch_to_thread(struct imcthread *thread) {
+    assert(!CURRENT_THREAD);
+    assert(thread->state != THREAD_STATE_DEAD);
+
+    CURRENT_THREAD = thread;
+    swapcontext(&MASTER_CTX, &(thread->ctx));
+}
+
+static void imcthread_entry_point(int tid) {
+    struct imcthread *thread = THREADS[tid];
+    thread->state = THREAD_STATE_ALIVE;
+    CURRENT_THREAD = thread;
+
+    void *result = thread->fn(thread->arg);
+
+    thread->retval = result;
+    thread->state = THREAD_STATE_DEAD;
+
+    imcthread_yield();
+}
diff --git a/libptimc/libptimc.h b/libptimc/libptimc.h
new file mode 100644
index 0000000..c6314dd
--- /dev/null
+++ b/libptimc/libptimc.h
@@ -0,0 +1,49 @@
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdio.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <ucontext.h>
+#include "libimc.h"
+
+enum thread_state {
+    THREAD_STATE_FETUS,
+    THREAD_STATE_ALIVE,
+    THREAD_STATE_DEAD,
+};
+
+typedef struct imcthread {
+    void *(*fn)(void *);
+    void *arg;
+    enum thread_state state;
+    int id;
+    struct imcthread *waiting_on;
+    void *retval;
+
+    ucontext_t ctx;
+} *imcthread_t;
+
+typedef int imcthread_attr_t;
+
+int imcthread_create(imcthread_t *thread,
+                     // only support NULL attr for now
+                     imcthread_attr_t *attr,
+                     void *(*start_routine)(void *),
+                     void *arg);
+int imcthread_yield(void);
+int imcthread_join(imcthread_t thread, void **retval);
+
+int imcthread_yieldh(hash_t hash);
+int imcthread_joinh(imcthread_t thread, void **retval, hash_t hash);
+
+void check_main(void);
+
+extern void imc_check_main(void);
+
+#ifdef __cplusplus
+}
+#endif