Address #189 ensuring socket locks are released

The code previous assume exception-free execution of critical blocks
between lock acquire() and lock release(); however, in Python exceptions
can be thrown in many situations which would then result in a dead-lock
of the entire program using pigpio.

This is resolved by using the acquire/try/finally/release pattern to
ensure that the lock is always released, even when an exception occurs.

Also addresses #186, but takes a slightly different approach by using
RLock to handle the nested lock requirement, which overall should be
safer because it handles additional situations that can cause a
deadlock.

pigpio.py

@@ -860,7 +860,7 @@ class _socklock:
    """
    def __init__(self):
       self.s = None
-      self.l = threading.Lock()
+      self.l = threading.RLock()
 
 class error(Exception):
    """pigpio module exception"""
@@ -970,7 +970,7 @@ def _u2i(uint32):
          raise error(error_text(v))
    return v
 
-def _pigpio_command(sl, cmd, p1, p2, rl=True):
+def _pigpio_command(sl, cmd, p1, p2):
    """
    Runs a pigpio socket command.
 
@@ -980,12 +980,14 @@ def _pigpio_command(sl, cmd, p1, p2, rl=True):
     p2:= command parameter 2 (if applicable).
    """
    sl.l.acquire()
+   try:
       sl.s.send(struct.pack('IIII', cmd, p1, p2, 0))
       dummy, res = struct.unpack('12sI', sl.s.recv(_SOCK_CMD_LEN))
-   if rl: sl.l.release()
+   finally:
+      sl.l.release()
    return res
 
-def _pigpio_command_ext(sl, cmd, p1, p2, p3, extents, rl=True):
+def _pigpio_command_ext(sl, cmd, p1, p2, p3, extents):
    """
    Runs an extended pigpio socket command.
 
@@ -1003,9 +1005,11 @@ def _pigpio_command_ext(sl, cmd, p1, p2, p3, extents, rl=True):
       else:
          ext.extend(x)
    sl.l.acquire()
+   try:
       sl.s.sendall(ext)
       dummy, res = struct.unpack('12sI', sl.s.recv(_SOCK_CMD_LEN))
-   if rl: sl.l.release()
+   finally:
+      sl.l.release()
    return res
 
 class _event_ADT:
@@ -2854,12 +2858,14 @@ class pi():
          # process read failure
       ...
       """
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
-      bytes = u2i(_pigpio_command(self.sl, _PI_CMD_I2CRK, handle, reg, False))
+      try:
+         bytes = u2i(_pigpio_command(self.sl, _PI_CMD_I2CRK, handle, reg))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -2904,13 +2910,15 @@ class pi():
       ## extension ##
       # s len data bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_I2CPK, handle, reg, len(data), [data], False))
+            self.sl, _PI_CMD_I2CPK, handle, reg, len(data), [data]))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -2982,13 +2990,15 @@ class pi():
       # I count
       extents = [struct.pack("I", count)]
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_I2CRI, handle, reg, 4, extents, False))
+            self.sl, _PI_CMD_I2CRI, handle, reg, 4, extentse))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -3013,13 +3023,15 @@ class pi():
       (count, data) = pi.i2c_read_device(h, 12)
       ...
       """
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(
-         _pigpio_command(self.sl, _PI_CMD_I2CRD, handle, count, False))
+            _pigpio_command(self.sl, _PI_CMD_I2CRD, handle, count))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -3115,13 +3127,15 @@ class pi():
       ## extension ##
       # s len data bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_I2CZ, handle, 0, len(data), [data], False))
+            self.sl, _PI_CMD_I2CZ, handle, 0, len(data), [data]))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -3284,13 +3298,15 @@ class pi():
       ## extension ##
       # s len data bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_BSPIX, CS, 0, len(data), [data], False))
+            self.sl, _PI_CMD_BSPIX, CS, 0, len(data), [data]))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -3421,13 +3437,15 @@ class pi():
       ## extension ##
       # s len data bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_BI2CZ, SDA, 0, len(data), [data], False))
+            self.sl, _PI_CMD_BI2CZ, SDA, 0, len(data), [data]))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -3551,9 +3569,10 @@ class pi():
       ## extension ##
       # s len data bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_BSCX, bsc_control, 0, len(data), [data], False))
+            self.sl, _PI_CMD_BSCX, bsc_control, 0, len(data), [data]))
          if bytes > 0:
             rx = self._rxbuf(bytes)
             status = struct.unpack('I', rx[0:4])[0]
@@ -3563,6 +3582,7 @@ class pi():
             status = bytes
             bytes = 0
             data = bytearray(b'')
+      finally:
          self.sl.l.release()
       return status, bytes, data
 
@@ -3818,13 +3838,15 @@ class pi():
          # error path
       ...
       """
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command(
-         self.sl, _PI_CMD_SPIR, handle, count, False))
+            self.sl, _PI_CMD_SPIR, handle, count))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -3882,13 +3904,15 @@ class pi():
       ## extension ##
       # s len data bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_SPIX, handle, 0, len(data), [data], False))
+            self.sl, _PI_CMD_SPIX, handle, 0, len(data), [data]))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -3988,13 +4012,15 @@ class pi():
          # process read data
       ...
       """
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(
-         _pigpio_command(self.sl, _PI_CMD_SERR, handle, count, False))
+            _pigpio_command(self.sl, _PI_CMD_SERR, handle, count))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -4217,9 +4243,10 @@ class pi():
       (s, pars) = pi.script_status(sid)
       ...
       """
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(
-         _pigpio_command(self.sl, _PI_CMD_PROCP, script_id, 0, False))
+            _pigpio_command(self.sl, _PI_CMD_PROCP, script_id, 0))
          if bytes > 0:
             data = self._rxbuf(bytes)
             pars = struct.unpack('11i', _str(data))
@@ -4228,6 +4255,7 @@ class pi():
          else:
             status = bytes
             params = ()
+      finally:
          self.sl.l.release()
       return status, params
 
@@ -4308,13 +4336,15 @@ class pi():
       (count, data) = pi.bb_serial_read(4)
       ...
       """
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
           bytes = u2i(
-         _pigpio_command(self.sl, _PI_CMD_SLR, user_gpio, 10000, False))
+             _pigpio_command(self.sl, _PI_CMD_SLR, user_gpio, 10000))
           if bytes > 0:
              data = self._rxbuf(bytes)
           else:
              data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -4410,13 +4440,15 @@ class pi():
       ## extension ##
       # s len argx bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_CF2, arg1, retMax, len(argx), [argx], False))
+            self.sl, _PI_CMD_CF2, arg1, retMax, len(argx), [argx]))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -4610,13 +4642,15 @@ class pi():
          # process read data
       ...
       """
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(
-         _pigpio_command(self.sl, _PI_CMD_FR, handle, count, False))
+            _pigpio_command(self.sl, _PI_CMD_FR, handle, count))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data
 
@@ -4716,13 +4750,15 @@ class pi():
       ## extension ##
       # s len data bytes
 
-      # Don't raise exception.  Must release lock.
+      self.sl.l.acquire()
+      try:
          bytes = u2i(_pigpio_command_ext(
-         self.sl, _PI_CMD_FL, 60000, 0, len(fpattern), [fpattern], False))
+            self.sl, _PI_CMD_FL, 60000, 0, len(fpattern), [fpattern]))
          if bytes > 0:
             data = self._rxbuf(bytes)
          else:
             data = ""
+      finally:
          self.sl.l.release()
       return bytes, data