interrupt.c

/*
Example of instantiating of the WebAssembly module and invoking its exported
function.

You can build using cmake:

mkdir build && cd build && cmake .. && \
  cmake --build . --target wasmtime-interrupt
*/

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <wasm.h>
#include <wasmtime.h>

#ifdef _WIN32
static void spawn_interrupt(wasm_engine_t *engine) {
  wasmtime_engine_increment_epoch(engine);
}
#else
#include <pthread.h>
#include <time.h>

static void *helper(void *_engine) {
  wasm_engine_t *engine = _engine;
  struct timespec sleep_dur;
  sleep_dur.tv_sec = 1;
  sleep_dur.tv_nsec = 0;
  nanosleep(&sleep_dur, NULL);
  printf("Sending an interrupt\n");
  wasmtime_engine_increment_epoch(engine);
  return 0;
}

static void spawn_interrupt(wasm_engine_t *engine) {
  pthread_t child;
  int rc = pthread_create(&child, NULL, helper, engine);
  assert(rc == 0);
}
#endif

static void exit_with_error(const char *message, wasmtime_error_t *error,
                            wasm_trap_t *trap);

int main() {
  // Create a `wasm_store_t` with interrupts enabled
  wasm_config_t *config = wasm_config_new();
  assert(config != NULL);
  wasmtime_config_epoch_interruption_set(config, true);
  wasm_engine_t *engine = wasm_engine_new_with_config(config);
  assert(engine != NULL);
  wasmtime_store_t *store = wasmtime_store_new(engine, NULL, NULL);
  assert(store != NULL);
  wasmtime_context_t *context = wasmtime_store_context(store);

  // Configure the epoch deadline after which WebAssembly code will trap.
  wasmtime_context_set_epoch_deadline(context, 1);

  // Read our input file, which in this case is a wasm text file.
  FILE *file = fopen("examples/interrupt.wat", "r");
  assert(file != NULL);
  fseek(file, 0L, SEEK_END);
  size_t file_size = ftell(file);
  fseek(file, 0L, SEEK_SET);
  wasm_byte_vec_t wat;
  wasm_byte_vec_new_uninitialized(&wat, file_size);
  if (fread(wat.data, file_size, 1, file) != 1) {
    printf("> Error loading module!\n");
    return 1;
  }
  fclose(file);

  // Parse the wat into the binary wasm format
  wasm_byte_vec_t wasm;
  wasmtime_error_t *error = wasmtime_wat2wasm(wat.data, wat.size, &wasm);
  if (error != NULL)
    exit_with_error("failed to parse wat", error, NULL);
  wasm_byte_vec_delete(&wat);

  // Now that we've got our binary webassembly we can compile our module.
  wasmtime_module_t *module = NULL;
  error = wasmtime_module_new(engine, (uint8_t *)wasm.data, wasm.size, &module);
  wasm_byte_vec_delete(&wasm);
  if (error != NULL)
    exit_with_error("failed to compile module", error, NULL);

  wasm_trap_t *trap = NULL;
  wasmtime_instance_t instance;
  error = wasmtime_instance_new(context, module, NULL, 0, &instance, &trap);
  if (error != NULL || trap != NULL)
    exit_with_error("failed to instantiate", error, trap);
  wasmtime_module_delete(module);

  // Lookup our `run` export function
  wasmtime_extern_t run;
  bool ok = wasmtime_instance_export_get(context, &instance, "run", 3, &run);
  assert(ok);
  assert(run.kind == WASMTIME_EXTERN_FUNC);

  // Spawn a thread to send us an interrupt after a period of time.
  spawn_interrupt(engine);

  // And call it!
  printf("Entering infinite loop...\n");
  error = wasmtime_func_call(context, &run.of.func, NULL, 0, NULL, 0, &trap);
  assert(error == NULL);
  assert(trap != NULL);
  printf("Got a trap!...\n");

  wasmtime_store_delete(store);
  wasm_engine_delete(engine);
  return 0;
}

static void exit_with_error(const char *message, wasmtime_error_t *error,
                            wasm_trap_t *trap) {
  fprintf(stderr, "error: %s\n", message);
  wasm_byte_vec_t error_message;
  if (error != NULL) {
    wasmtime_error_message(error, &error_message);
    wasmtime_error_delete(error);
  } else {
    wasm_trap_message(trap, &error_message);
    wasm_trap_delete(trap);
  }
  fprintf(stderr, "%.*s\n", (int)error_message.size, error_message.data);
  wasm_byte_vec_delete(&error_message);
  exit(1);
}