[7dc855c] | 1 | #!/usr/local/bin/python |
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| 2 | |
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| 3 | from threading import Lock, Condition |
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| 4 | |
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| 5 | class synch_store: |
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| 6 | """ |
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| 7 | Serialized write-once dictionary. Threads reading before the value for a |
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| 8 | key is assigned wait for the assignment, though polling is an option. Keys |
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| 9 | may also be deleted, though deleting a value too closely after the set may |
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| 10 | deadlock threads waiting for the assignment. |
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| 11 | """ |
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[5e3d889] | 12 | |
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| 13 | # Thrown if a key is assigned more than once |
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[7dc855c] | 14 | class CollisionError(Exception): pass |
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[5e3d889] | 15 | |
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| 16 | # Thrown if a non-existant key is deleted |
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[7dc855c] | 17 | class BadDeletionError(Exception): pass |
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| 18 | |
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[ef252e9] | 19 | # Thrown if a key is specified with a white space |
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| 20 | class BadKeyError(Exception): pass |
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| 21 | |
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[5e3d889] | 22 | # A value in the dict. Each has its own condition (and lock) for threads |
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| 23 | # to wait on. |
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[7dc855c] | 24 | class synch_value: |
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[5e3d889] | 25 | # The synch_value constructor. |
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| 26 | def __init__(self, value=None): |
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[7dc855c] | 27 | self.value = value |
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| 28 | self.condition = Condition() |
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| 29 | |
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[5e3d889] | 30 | # Debugging representation |
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[7dc855c] | 31 | def __str__(self): |
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[5e3d889] | 32 | return "value %s cond %s" % (self.value, self.condition) |
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[7dc855c] | 33 | |
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[5e3d889] | 34 | # The synch_store constructor. Note that the store has its own lock for |
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| 35 | # serializing additions to the dict. |
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[7dc855c] | 36 | def __init__(self): |
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| 37 | self.main_lock = Lock() |
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| 38 | self.values = { } |
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| 39 | |
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[5e3d889] | 40 | # Set the value in the dict. If threads are waiting, wake them. |
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[7dc855c] | 41 | def set_value(self, key, value): |
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[ef252e9] | 42 | if key.find(' ') != -1: |
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| 43 | raise self.BadKeyError("Whitespace is not allowed in keys") |
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| 44 | |
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[7dc855c] | 45 | self.main_lock.acquire() |
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| 46 | if self.values.has_key(key): |
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| 47 | v = self.values[key] |
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| 48 | v.condition.acquire() |
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| 49 | self.main_lock.release() |
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| 50 | if v.value is None: |
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| 51 | v.value = value |
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| 52 | v.condition.notifyAll() |
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| 53 | v.condition.release() |
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| 54 | else: |
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| 55 | v.condition.release() |
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| 56 | raise synch_store.CollisionError("%s already set" % key) |
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| 57 | else: |
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[5e3d889] | 58 | self.values[key] = synch_store.synch_value(value) |
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[7dc855c] | 59 | self.main_lock.release() |
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| 60 | |
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[5e3d889] | 61 | # Ask for the value. If wait is true, wait until the key is set, if it is |
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| 62 | # not already. If wait is false, poll. |
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[7dc855c] | 63 | def get_value(self, key, wait=True): |
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| 64 | self.main_lock.acquire() |
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| 65 | if not self.values.has_key(key): |
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[5e3d889] | 66 | self.values[key] = synch_store.synch_value() |
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[7dc855c] | 67 | v = self.values[key] |
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| 68 | v.condition.acquire() |
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| 69 | self.main_lock.release() |
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| 70 | |
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| 71 | while v.value is None: |
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| 72 | if wait: v.condition.wait() |
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| 73 | else: break |
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| 74 | rv = v.value |
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| 75 | v.condition.release() |
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| 76 | return rv |
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| 77 | |
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[5e3d889] | 78 | # Remove the key from the shared store. If the key is not present or has |
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| 79 | # never been set, fail. Otherwise, wake any waiting threads (there |
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| 80 | # shouldn't be any) and remove the value and key from the store. |
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[7dc855c] | 81 | def del_value(self, key): |
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| 82 | self.main_lock.acquire() |
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| 83 | if self.values.has_key(key): |
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| 84 | v = self.values[key] |
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| 85 | v.condition.acquire() |
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| 86 | if v.value is not None: |
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| 87 | del self.values[key] |
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| 88 | self.main_lock.release() |
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| 89 | v.condition.notifyAll() |
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| 90 | else: |
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| 91 | self.main_lock.release() |
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| 92 | raise synch_store.BadDeletionError("%s has not been set" % key) |
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| 93 | else: |
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| 94 | self.main_lock.release() |
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| 95 | raise synch_store.BadDeletionError("%s does not exist yet" % key) |
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| 96 | |
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[ef252e9] | 97 | def all_keys(self): |
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| 98 | self.main_lock.acquire() |
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| 99 | rv = [ k for k in self.values.keys()] |
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| 100 | self.main_lock.release() |
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| 101 | return rv |
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| 102 | |
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| 103 | # Save the store contents to a file in a simple way |
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| 104 | def save(self, filename): |
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| 105 | self.main_lock.acquire() |
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| 106 | f = open(filename, 'w') |
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| 107 | for k, v in self.values.items(): |
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| 108 | self.values[k].condition.acquire() |
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| 109 | if self.values[k].value is not None: |
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| 110 | print >> f, "%s %s" % ( k, str(self.values[k].value)) |
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| 111 | else: |
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| 112 | print >> f, "%s" % k |
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| 113 | self.values[k].condition.release() |
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| 114 | self.main_lock.release() |
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| 115 | f.close() |
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| 116 | |
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| 117 | # Load the store contents from a file |
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| 118 | def load(self, filename): |
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| 119 | self.main_lock.acquire() |
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| 120 | self.values = { } |
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| 121 | f = open(filename, 'r') |
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| 122 | for l in f: |
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| 123 | i = l.find(' ') |
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| 124 | if i != -1: self.values[l[:i]] = synch_store.synch_value(l[i+1:]) |
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| 125 | else: self.values[l] = synch_store.synch_value() |
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| 126 | f.close() |
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| 127 | self.main_lock.release() |
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| 128 | |
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[5e3d889] | 129 | # A debugging representation |
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[7dc855c] | 130 | def __str__(self): |
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| 131 | rv = "" |
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| 132 | self.main_lock.acquire() |
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| 133 | for k, v in self.values.items(): |
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| 134 | self.values[k].condition.acquire() |
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[5e3d889] | 135 | rv += "%s: %s\n" % ( k, str(self.values[k])) |
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[7dc855c] | 136 | self.values[k].condition.release() |
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| 137 | self.main_lock.release() |
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| 138 | return rv |
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| 139 | |
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| 140 | #debugging scaffolding, left here in case we have problems |
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| 141 | if __name__ == '__main__': |
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| 142 | from threading import currentThread, Thread |
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| 143 | from time import sleep |
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| 144 | |
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| 145 | def get_val(k, ss, wait=True): |
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| 146 | print "%s: getting %s" % (currentThread(), k) |
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| 147 | v = ss.get_value(k, wait) |
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| 148 | print "%s: %s is %s" % (currentThread(), k, v) |
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| 149 | |
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| 150 | |
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| 151 | def set_val(k, v, ss): |
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| 152 | print "setting %s to %s" % (k, v) |
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| 153 | try: |
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| 154 | ss.set_value(k, v) |
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| 155 | except synch_store.CollisionError, e: |
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| 156 | print "Error: %s" %e |
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| 157 | return |
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| 158 | print "Done with set" |
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| 159 | |
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| 160 | def del_val(k, ss): |
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| 161 | print "deleteing %s" % k |
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| 162 | try: |
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| 163 | ss.del_value(k) |
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| 164 | except synch_store.BadDeletionError, e: |
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| 165 | print "Error: %s" %e |
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| 166 | return |
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| 167 | print "Done with del" |
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| 168 | |
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| 169 | |
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| 170 | ss = synch_store() |
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| 171 | ss.set_value('b', 'initial') |
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| 172 | print ss |
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| 173 | |
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| 174 | for i in range(0,10): |
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| 175 | t = Thread(target=get_val, args=('a', ss, i % 2 == 1)) |
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| 176 | t.start() |
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| 177 | t = Thread(target=set_val, args=('a', '1', ss)) |
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| 178 | t.start() |
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| 179 | for i in range(0,10): |
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| 180 | t = Thread(target=get_val, args=('a', ss)) |
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| 181 | t.start() |
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| 182 | |
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| 183 | print ss |
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| 184 | t = Thread(target=del_val, args=('a', ss)) |
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| 185 | t.start() |
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| 186 | print ss |
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| 187 | |
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| 188 | |
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