SimpleDateFormat doesn't appear to be thread safe. This fact is not
documented, and on first blush it is inexplicable, as SimpleDateFormat's
abstract state shouldn't be affected by its use.

The enclosed program illustrates SimpleDateFormat formatting incorrectly when used in a threaded environment. This program also dies with array index errors occasionally.

I will be disappointed if this problem is "fixed" by adding "synchronized" to the format method of SimpleDateFormat; I don't want my programs serialized that way.

vedas$ cat -n Main.java
     1 import java.text.SimpleDateFormat;
     2 import java.util.Date;
     3
     4 class Main {
     5 static int n = 0;
     6
     7 static final String dateFormatString = "yyyy-MM-dd kk:mm:ss:SSS";
     8 static final SimpleDateFormat dateFormat =
     9 new SimpleDateFormat(dateFormatString);
    10
    11 private static void makethread() {
    12 Thread t = new Thread() {
    13 public void run() {
    14 for (;;) {
    15 String s = dateFormat.format(new Date());
    16 if (s.length() != dateFormatString.length()) {
    17 System.out.println(s);
    18 if (n++ > 100) System.exit(1);
    19 }
    20 try { Thread.sleep(1); }
    21 catch (InterruptedException e) {}
    22 }
    23 }
    24 };
    25 t.start();
    26 }
    27
    28 static public void main(String[] args) {
    29 makethread();
    30 makethread();
    31 makethread();
    32 makethread();
    33 makethread();
    34 makethread();
    35 makethread();
    36 makethread();
    37 makethread();
    38 makethread();
    39 try { Thread.sleep(60*60*1000); }
    40 catch (InterruptedException e) {}
    41 System.exit(0);
    42 }
    43 }
    44
vedas$ make
/gafter/neal-gjc/build/sparc/bin/javac Main.java
/gafter/neal-gjc/build/sparc/bin/java Main
2000-10-20 14:48:041:889
2000-0010-20 14:48:41:943
2000-10-20 14:48:41:0931
2000-10-20 14:48:42:0088
2000-10-20 14:048:42:130
2000-10-20 014:48:42:300
2000-10-20 14:48:042:310
2000-10-20 14:048:42:350
2000-10-20 0014:48:42:430
2000-10-020 14:48:42:450
2000-010-20 14:48:42:490
2000-10-20 14:48:042:720
2000-10-0020 14:48:42:780
2000-10-20 14:048:42:810
2000-10-20 14:48:42:0812
2000-10-20 14:48:042:878
2000-10-20 014:48:42:940
2000-10-20 14:48:043:190
2000-10-20 014:48:43:220
2000-10-20 14:0048:43:359
2000-10-20 14:48:0043:443
2000-0010-20 14:48:43:460
2000-10-20 0014:48:43:513
2000-10-20 14:48:0043:618
2000-10-20 14:48:43:0641
2000-10-020 14:48:43:868
2000-10-20 14:48:0043:883
2000-0010-20 14:48:43:943
2000-10-20 14:48:43:0943
2000-10-20 14:0048:0043:996
2000-10-20 14:048:44:042
2000-10-20 14:048:44:189
2000-10-20 14:048:44:219
2000-10-020 14:48:44:304
2000-10-20 14:48:44:0331
2000-10-20 14:048:44:404
2000-10-20 14:48:0044:444
2000-10-20 0014:48:44:474
2000-10-20 14:048:44:629
2000-10-20 14:048:44:849
2000-10-20 14:48:0044:964
2000-010-20 14:48:45:150
2000-10-20 14:48:045:460
2000-10-20 14:48:045:510
2000-10-20 14:48:45:0521
2000-10-20 014:48:45:578
2000-10-20 14:48:45:0578
2000-10-0020 14:48:045:650
2000-10-20 14:48:045:759
2000-10-20 14:48:045:950
2000-10-20 14:48:0046:329
2000-10-20 14:0048:46:410
2000-10-20 14:48:0046:579
2000-10-20 14:0048:0046:0614
2000-10-20 14:48:0046:663
2000-10-20 14:48:46:0651
2000-10-20 14:48:46:0981
2000-10-20 14:0048:47:129
2000-10-20 14:48:047:170
2000-010-20 14:48:47:229
2000-10-20 14:48:0047:273
2000-0010-20 14:48:0047:0324
2000-10-20 14:48:47:0401
2000-10-20 14:48:047:460
2000-10-20 14:0048:47:523
2000-10-20 14:0048:47:0544
2000-10-20 0014:48:47:649
2000-10-20 14:48:47:0661
2000-0010-20 14:0048:47:749
2000-0010-20 14:48:47:777
2000-10-20 14:0048:47:868
2000-10-20 14:48:47:0951
2000-10-20 0014:48:48:024
2000-10-0020 14:48:47:054
2000-10-0020 14:48:48:129
2000-10-20 14:48:48:0201
2000-10-20 14:48:48:0231
2000-10-20 14:48:48:0341
2000-0010-20 14:48:48:358
2000-0010-20 14:48:48:420
2000-10-20 14:48:0048:460
2000-10-20 14:0048:048:510
2000-10-20 14:0048:48:660
2000-10-20 14:0048:48:747
2000-10-20 14:48:48:0774
2000-10-20 14:48:0048:980
2000-0010-20 14:48:49:009
2000-10-20 0014:48:48:030
2000-10-20 0014:48:49:041
2000-10-20 14:48:0049:249
2000-10-20 14:48:049:369
2000-10-20 14:48:0049:497
2000-10-020 14:48:49:497
2000-010-20 14:48:49:520
2000-0010-20 14:48:49:600
2000-10-020 14:48:49:740
2000-10-20 14:0048:50:079
2000-10-20 14:48:0050:190
2000-10-20 14:48:50:0364
2000-10-20 14:0048:50:474
2000-10-20 14:48:0050:514
2000-10-20 14:48:50:0551
2000-10-20 14:48:50:0640
*** Error code 1
make: Fatal error: Command failed for target `all'
vedas$