Merge pull request #32 from badgeteam/mutex

Support for not using timeouts on mutexes.

include/mutex.h

@@ -30,12 +30,14 @@ void mutex_init_shared(badge_err_t *ec, mutex_t *mutex);
 // Clean up the mutex.
 void mutex_destroy(badge_err_t *ec, mutex_t *mutex);
 // Try to acquire `mutex` within `max_wait_us` microseconds.
+// If `max_wait_us` is too long or negative, do not use the timeout.
 // Returns true if the mutex was successully acquired.
 bool mutex_acquire(badge_err_t *ec, mutex_t *mutex, timestamp_us_t max_wait_us);
 // Release `mutex`, if it was initially acquired by this thread.
 // Returns true if the mutex was successfully released.
 bool mutex_release(badge_err_t *ec, mutex_t *mutex);
 // Try to acquire a share in `mutex` within `max_wait_us` microseconds.
+// If `max_wait_us` is too long or negative, do not use the timeout.
 // Returns true if the share was successfully acquired.
 bool mutex_acquire_shared(badge_err_t *ec, mutex_t *mutex, timestamp_us_t max_wait_us);
 // Release `mutex`, if it was initially acquired by this thread.

include/time.h

@@ -9,6 +9,13 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#define FREQUENCY_HZ_MIN INT32_MIN
+#define FREQUENCY_HZ_MAX INT32_MAX
+#define TIMESTAMP_US_MIN INT64_MIN
+#define TIMESTAMP_US_MAX INT64_MAX
+#define TIMER_VALUE_MIN  INT64_MIN
+#define TIMER_VALUE_MAX  INT64_MAX
+
 typedef int32_t frequency_hz_t;
 typedef int64_t timestamp_us_t;
 typedef int64_t timer_value_t;

src/mutex.c

@@ -101,7 +101,13 @@ bool mutex_acquire(badge_err_t *ec, mutex_t *mutex, timestamp_us_t timeout) {
         badge_err_set(ec, ELOC_UNKNOWN, ECAUSE_ILLEGAL);
         return false;
     }
-    timeout += time_us();
+    // Compute timeout.
+    timestamp_us_t now = time_us();
+    if (timeout < 0 || now + timeout < now) {
+        timeout = TIMESTAMP_US_MAX;
+    } else {
+        timeout += now;
+    }
     // Await the shared portion to reach 0 and then lock.
     if (await_swap_atomic_int(&mutex->shares, timeout, 0, EXCLUSIVE_MAGIC, memory_order_acquire)) {
         // If that succeeds, the mutex was acquired.
@@ -121,7 +127,7 @@ bool mutex_release(badge_err_t *ec, mutex_t *mutex) {
         badge_err_set(ec, ELOC_UNKNOWN, ECAUSE_ILLEGAL);
         return false;
     }
-    if (await_swap_atomic_int(&mutex->shares, time_us() + 10000000, EXCLUSIVE_MAGIC, 0, memory_order_release)) {
+    if (await_swap_atomic_int(&mutex->shares, TIMESTAMP_US_MAX, EXCLUSIVE_MAGIC, 0, memory_order_release)) {
         // Successful release.
         badge_err_set_ok(ec);
         return true;
@@ -143,7 +149,13 @@ bool mutex_acquire_shared(badge_err_t *ec, mutex_t *mutex, timestamp_us_t timeou
         badge_err_set(ec, ELOC_UNKNOWN, ECAUSE_ILLEGAL);
         return false;
     }
-    timeout += time_us();
+    // Compute timeout.
+    timestamp_us_t now = time_us();
+    if (timeout < 0 || now + timeout < now) {
+        timeout = TIMESTAMP_US_MAX;
+    } else {
+        timeout += now;
+    }
     // Take a share.
     if (thresh_add_atomic_int(&mutex->shares, timeout, EXCLUSIVE_MAGIC, memory_order_acquire)) {
         // If that succeeds, the mutex was successfully acquired.